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IMA Newsletter #395

September 2009

2009-2010 Program

See http://www.ima.umn.edu/2009-2010/ for a full description of the 2009-2010 program on Complex Fluids and Complex Flows.

2009-2010 IMA Participating Institutions Conferences

IMA Events

IMA Tutorial

An Introduction to Funny (Complex) Fluids: Rheology, Modeling and Theorems

September 12-13, 2009

Organizers: L. Pamela Cook (University of Delaware), Michael D. Graham (University of Wisconsin), Christopher Macosko (University of Minnesota Twin Cities), Michael Renardy (Virginia Polytechnic Institute and State University)

IMA Annual Program Year Workshop

Flowing Complex Fluids: Rheological measurements and constitutive modeling

September 14-18, 2009

Organizers: Peter Constantin (University of Chicago), L. Pamela Cook (University of Delaware), Michael D. Graham (University of Wisconsin), Ronald G. Larson (University of Michigan), Gareth Huw Mckinley (Massachusetts Institute of Technology)

Public Lecture

Arnold Family Lecture: Donald G. Saari: Chaotic elections: why don't we elect who voters really want?

September 22, 2009

Speakers: Donald G. Saari (University of California)
Schedule

Wednesday, September 2

10:45am-11:15amCoffee breakLind Hall 400

Thursday, September 3

3:00pm-3:30pmCoffee breakLind Hall 400

Friday, September 4

3:00pm-3:30pmCoffee breakLind Hall 400

Monday, September 7

All DayLabor Day. The IMA is closed.

Tuesday, September 8

10:45am-11:15amCoffee breakLind Hall 400

Wednesday, September 9

10:00am-10:30amCoffee breakLind Hall 400
10:30am-12:00pmOrientation for Postdocs and Long-Term Visitors
  • Introductions
  • Presentation by Michelle Radtke about social activities web page
  • Planning scientific activities - course, seminars, focus groups
  • Discussions with postdocs
Lind Hall 305
2:30pm-3:20pmTopics in the theory of the Navier-Stokes equationsVladimir Sverak (University of Minnesota)Lind Hall 305

Thursday, September 10

All DayIMA Postdoc Show and Tell
Lind Hall 305

9:30-9:40 Nusret Balci
9:42-9:52 Chi Hin Chan
9:54-10:04 Randy Ewoldt
10:06-10:16 Pawel Konieczny
10:18-10:28 Zhi George Lin
10:30-10:40 Kara Maki

10:42-10:50 BREAK

10:50-11:00 Cecilia Ortiz-Duenas
11:02-11:12 Tsuyoshi Yoneda
11:14-11:24 Hyejin Kim
11:26-11:36 Shuanglin Shao
11:38-11:48 Lijian Jiang
11:50-12:00 Weigang Zhong

Lunch and Posters
Lind Hall 400
12:00-1:30

Long-Term Visitor Introductions
Lind Hall 305
1:30-2:30

Friday, September 11

10:45am-11:15amCoffee breakLind Hall 400
1:25pm-2:25pmRobust portfolio optimization using a cross sectional factor modelChristopher Bemis (Whitebox Advisors)Vincent Hall 570 IPS

Saturday, September 12

8:15am-8:45amRegistration and coffeeEE/CS 3-176 T9.12-13.09
8:45am-9:00amWelcome to the IMAFadil Santosa (University of Minnesota)EE/CS 3-180 T9.12-13.09
9:00am-10:30amUnderstanding silly putty, snail slime and other funny fluidsChristopher Macosko (University of Minnesota)EE/CS 3-180 T9.12-13.09
10:30am-10:45amCoffee breakEE/CS 3-176 T9.12-13.09
10:45am-12:15pmUnderstanding silly putty, snail slime and other funny fluids (continued)Christopher Macosko (University of Minnesota)EE/CS 3-180 T9.12-13.09
12:15pm-2:00pmLunch T9.12-13.09
2:00pm-3:30pmRheological modeling from the mesoscopic point of viewMichael D. Graham (University of Wisconsin)EE/CS 3-180 T9.12-13.09
3:30pm-4:00pmCoffee breakEE/CS 3-176 T9.12-13.09
4:00pm-5:00pmRheological modeling from the mesoscopic point of view (continued)Michael D. Graham (University of Wisconsin)EE/CS 3-180 T9.12-13.09

Sunday, September 13

10:00am-10:30amCoffeeEE/CS 3-176 T9.12-13.09
10:30am-12:00pmTurning polymeric liquids into theoremsMichael Renardy (Virginia Polytechnic Institute and State University)EE/CS 3-180 T9.12-13.09
12:00pm-1:30pmLunch T9.12-13.09
1:30pm-3:00pmTurning polymeric liquids into theorems (continued)Michael Renardy (Virginia Polytechnic Institute and State University)EE/CS 3-180 T9.12-13.09

Monday, September 14

All DayChair: Suzanne M. Fielding (University of Manchester) W9.14-18.09
8:15am-8:45amRegistration and coffee EE/CS 3-176 W9.14-18.09
8:45am-9:00amWelcome to the IMAFadil Santosa (University of Minnesota)EE/CS 3-180 W9.14-18.09
9:00am-9:45amPart 1: The nonlinear dynamics of DNA/polymers in extensional dominated flows: Solutions and melts

Part 2: Margination of micro- and nano- particles in the flow through microchannels
Eric S. G. Shaqfeh (Stanford University)EE/CS 3-180 W9.14-18.09
9:45am-9:50amQuestionsEE/CS 3-180 W9.14-18.09
9:50am-10:35amMicro and macro in the dynamics of dilute polymer solutionsRavi Prakash Jagadeeshan (Monash University)EE/CS 3-180 W9.14-18.09
10:35am-10:40amQuestionsEE/CS 3-180 W9.14-18.09
10:40am-11:00amCoffeeEE/CS 3-176 W9.14-18.09
11:00am-11:45amHierarchy of models for entangled polymersAlexei E. Likhtman (University of Reading)EE/CS 3-180 W9.14-18.09
11:45am-11:50amQuestionsEE/CS 3-180 W9.14-18.09
11:50am-1:30pmLunch W9.14-18.09
1:30pm-2:15pmHow well does the “standard” tube model for polymer dynamics work? Ronald G. Larson (University of Michigan)EE/CS 3-180 W9.14-18.09
2:15pm-2:20pmQuestionsEE/CS 3-180 W9.14-18.09
2:20pm-3:05pmDoes shear banding exist in polymer solutions?Peter D. Olmsted (University of Leeds)EE/CS 3-180 W9.14-18.09
3:05pm-3:10pmQuestionsEE/CS 3-180 W9.14-18.09
3:10pm-3:20pmGroup Photo W9.14-18.09
3:20pm-3:45pmCoffeeEE/CS 3-176 W9.14-18.09
3:45pm-4:15pmSecond chancesEE/CS 3-180 W9.14-18.09
4:15pm-6:00pmReception and Poster Session
Poster submissions welcome from all participants
Instructions
Lind Hall 400 W9.14-18.09
Flowing Complex Fluids: Rheological measurements and constitutive modeling James Adams (University of Surrey)
Dynamics and rheology of wormlike micelles emerging from particulate computer simulationsEdo S. Boek (Schlumberger Cambridge Research)
Simulations of mechanical failure in transient polymer networks Wim Briels (Universiteit Twente)
Director angle anchoring conditions and the dynamic moduli of nematic liquid crystal polymersEric Choate (University of North Carolina)
Vertical structures in shear thickening fluidsRobert Deegan (University of Michigan)
Using time-resolved SANS to understand the flow behavior of PB-PEO wormlike micellesJan Karel George Dhont (Forschungszentrum Jülich)
Pavlik Lettinga (Forschungszentrum Jülich)
On the origin of vorticity bandingJan Karel George Dhont (Forschungszentrum Jülich)
Pavlik Lettinga (Forschungszentrum Jülich)
Structure and rheology of nanoparticle gels and glassesAaron Paul Rust Eberle (University of Delaware)
Elastic instabilities in the flow of wormlike micelles Marc-Antoine Fardin (Université de Paris VII (Denis Diderot))
Self-organised criticality in sheared suspensionsEmmanouela Filippidi (New York University)
Vorticity and velocity banding in shear thickening solutions of wormlike micellesPeter Fischer (Eidgenössische TH Zürich-Zentrum)
Kinetic Monte Carlo simulations of flow-induced nucleation in polymer melts Richard S. Graham (University of Nottingham)
Peter D. Olmsted (University of Leeds)
Localized Jeffery-Hamel flows of viscoelastic fluidsThomas C. Hagen (University of Memphis)
A macroscopic closure approximation to the micro-macro FENE model for polymeric materials Yunkyong Hyon (University of Minnesota)
The Brinkman model for fast, viscous, and turbulent flows in porous mediaRoss Nicholas Ingram (University of Pittsburgh)
Viscoelastic flow in a two-dimensional collapsible channel Ravi Prakash Jagadeeshan (Monash University)
Processing, morphology and properties of graphene reinforced polymer nanocompositesHyunwoo Kim (University of Minnesota)
Stress relaxation of comb polymersL. Gary Leal (University of California, Santa Barbara)
3D-Imaging of cocontinuous blendsCarlos R. López Barrón (University of Minnesota)
Human tear film dynamics on an eye-shaped domain Kara Lee Maki (University of Minnesota)
Measurements of flow induced birefringence of complex fluids undergoing high rate deformations in microscale geometriesThomas Joseph Ober (Massachusetts Institute of Technology)
Influence of viscoelasticity on drop deformation in shearYuriko Renardy (Virginia Polytechnic Institute and State University)
Application of the discrete slip-link model to bidisperse linear systemsJay D. Schieber (Illinois Institute of Technology)
Influence of viscosity and elasticity on the statistical properties of meltblown polymer fibersDawud H. Tan (University of Minnesota)

Tuesday, September 15

All DayChair: Michael D. Graham (University of Wisconsin) W9.14-18.09
8:30am-9:00amCoffeeEE/CS 3-176 W9.14-18.09
9:00am-9:45amImaging the flow of concentrated suspensionsWilson Poon (University of Edinburgh)EE/CS 3-180 W9.14-18.09
9:45am-9:50amQuestionsEE/CS 3-180 W9.14-18.09
9:50am-10:35amMagnetorheology: Measurements, mechanisms and modelingDaniel J. Klingenberg (University of Wisconsin)EE/CS 3-180 W9.14-18.09
10:35am-10:40amQuestionsEE/CS 3-180 W9.14-18.09
10:40am-11:00amCoffeeEE/CS 3-176 W9.14-18.09
11:00am-11:45amMicrostructure and rheology relationships for concentrated colloidal dispersions: Shear thickening fluids and their applicationsNorman J. Wagner (University of Delaware)EE/CS 3-180 W9.14-18.09
11:45am-11:50amQuestionsEE/CS 3-180 W9.14-18.09
11:50am-1:30pmLunch W9.14-18.09
1:30pm-2:15pmMode coupling theory of colloid rheologyMichael E. Cates (University of Edinburgh)EE/CS 3-180 W9.14-18.09
2:15pm-2:20pmQuestionsEE/CS 3-180 W9.14-18.09
2:20pm-3:05pmViscoelasticity of bacterial biofilms probed by flexible microfluidic rheometryMichael J. Solomon (University of Michigan)EE/CS 3-180 W9.14-18.09
3:05pm-3:10pmQuestionsEE/CS 3-180 W9.14-18.09
3:10pm-3:30pmCoffeeEE/CS 3-176 W9.14-18.09
3:30pm-4:00pmSecond chancesEE/CS 3-180 W9.14-18.09
6:30pm-8:30pmWorkshop Dinner at KikugawaKikugawa at Riverplace
43 Main Street SE Minneapolis MN 55414
612-378-3006
W9.14-18.09

Wednesday, September 16

All DayChair: Gareth Huw Mckinley (Massachusetts Institute of Technology) W9.14-18.09
8:30am-9:00amCoffeeEE/CS 3-176 W9.14-18.09
9:00am-9:45amQuasi-static rheology of aqueous foamsGeorges F. Debrégeas (École Normale Supérieure)EE/CS 3-180 W9.14-18.09
9:45am-9:50amQuestionsEE/CS 3-180 W9.14-18.09
9:50am-10:35amX-ray scattering studies of flow-induced alignment in model polymer nanocompositesWesley R. Burghardt (Northwestern University)EE/CS 3-180 W9.14-18.09
10:35am-10:40amQuestionsEE/CS 3-180 W9.14-18.09
10:40am-11:00amCoffeeEE/CS 3-176 W9.14-18.09
11:00am-11:45amFilms and drops of active fluid Sriram Ramaswamy (Indian Institute of Science)EE/CS 3-180 W9.14-18.09
11:45am-11:50amQuestionsEE/CS 3-180 W9.14-18.09
11:50am-12:35pmThe secret life of yield stress fluids Phillipe Coussot (Centre National de la Recherche Scientifique (CNRS))EE/CS 3-180 W9.14-18.09
12:35pm-12:40pmQuestionsEE/CS 3-180 W9.14-18.09
12:40pm-3:30pmLunch and walk along the Mississippi River W9.14-18.09

Thursday, September 17

All DayChair: Peter Constantin (University of Chicago) W9.14-18.09
8:30am-9:00amCoffeeEE/CS 3-176 W9.14-18.09
9:00am-9:45amOriented assembly of anisotropic particles at interfacesKathleen J. Stebe (University of Pennsylvania)EE/CS 3-180 W9.14-18.09
9:45am-9:50amQuestionsEE/CS 3-180 W9.14-18.09
9:50am-10:35amOn the oscillatory tube flow of healthy human bloodRobert Gwyn Owens (University of Montreal)EE/CS 3-180 W9.14-18.09
10:35am-10:40amQuestionsEE/CS 3-180 W9.14-18.09
10:40am-11:00amCoffeeEE/CS 3-176 W9.14-18.09
11:00am-11:45amModels for dynamics of the human tear filmRichard J. Braun (University of Delaware)EE/CS 3-180 W9.14-18.09
11:45am-11:50amQuestionsEE/CS 3-180 W9.14-18.09
11:50am-1:15pmLunch W9.14-18.09
1:15pm-2:00pmUniquely biological challenges for rheology M. Gregory Forest (University of North Carolina)EE/CS 3-180 W9.14-18.09
2:00pm-2:05pmQuestionsEE/CS 3-180 W9.14-18.09
2:05pm-2:50pmRheology and dynamics of oscillated suspensions Jason E. Butler (University of Florida)EE/CS 3-180 W9.14-18.09
2:50pm-2:55pmQuestionsEE/CS 3-180 W9.14-18.09
2:55pm-3:15pmCoffeeEE/CS 3-176 W9.14-18.09
3:15pm-3:45pmSecond chancesEE/CS 3-180 W9.14-18.09

Friday, September 18

All DayChair: Ronald G. Larson (University of Michigan) W9.14-18.09
8:30am-9:00amCoffeeEE/CS 3-176 W9.14-18.09
9:00am-9:45amRheo-NMR of unusual shear banded flow in wormlike micellesPaul Terence Callaghan (Victoria University of Wellington)EE/CS 3-180 W9.14-18.09
9:45am-9:50amQuestionsEE/CS 3-180 W9.14-18.09
9:50am-10:35amHeterogeneous flows in complex fluidsAnnie Colin (Centre National de la Recherche Scientifique (CNRS))EE/CS 3-180 W9.14-18.09
10:35am-10:40amQuestionsEE/CS 3-180 W9.14-18.09
10:40am-10:50amCoffeeEE/CS 3-176 W9.14-18.09
10:50am-11:35amConstitutive modeling of the inhomogeneous response in steady and transient flows of entangled/micellar solutionsGareth Huw Mckinley (Massachusetts Institute of Technology)EE/CS 3-180 W9.14-18.09
11:35am-11:40amQuestionsEE/CS 3-180 W9.14-18.09
11:40am-1:00pmLunch W9.14-18.09
1:00pm-1:45pmDynamics of the shear banding flow in giant micellesSandra Lerouge (Université de Paris VII (Denis Diderot))EE/CS 3-180 W9.14-18.09
1:45pm-1:50pmQuestionsEE/CS 3-180 W9.14-18.09
1:50pm-2:35pmShear banding in complex fluids and biologically active suspensionsSuzanne M. Fielding (University of Durham)EE/CS 3-180 W9.14-18.09
2:35pm-2:40pmQuestions/Closing remarkEE/CS 3-180 W9.14-18.09

Monday, September 21

10:45am-11:15amCoffee breakLind Hall 400
2:30pm-3:20pmTopics in the theory of the Navier-Stokes equationsVladimir Sverak (University of Minnesota)Lind Hall 305

Tuesday, September 22

10:45am-11:15amCoffee breakLind Hall 400
11:15am-12:15pmMixed multiscale finite element methods using approximate global information and their applications in heterogeneous porous mediaLijian Jiang (University of Minnesota)Lind Hall 305 PS
6:30pm-7:00pmRefreshmentsWilley Hall 125 PUB9.22.09
7:00pm-8:00pmArnold family lecture – Chaotic elections: why don't we elect who voters really want? Donald G. Saari (University of California, Irvine)Willey Hall 125 PUB9.22.09

Wednesday, September 23

10:45am-11:15amCoffee breakLind Hall 400
11:15am-12:15pmStirring and mixing: Topology, optimization, and wallsJean-Luc Thiffeault (University of Wisconsin)Lind Hall 305 2009-2010Seminar
2:30pm-3:20pmTopics in the theory of the Navier-Stokes equationsVladimir Sverak (University of Minnesota)Lind Hall 305

Thursday, September 24

10:45am-11:15amCoffee breakLind Hall 400
3:30pm-4:30pmSchool of Math colloquium: Nonlinear/non-Gaussian time series and parameterJuan Mario Restrepo (University of Arizona)Vincent Hall 16

Friday, September 25

10:45am-11:15amCoffee breakLind Hall 400

Monday, September 28

10:45am-11:15amCoffee breakLind Hall 400
2:30pm-3:20pmTopics in the theory of the Navier-Stokes equationsVladimir Sverak (University of Minnesota)Lind Hall 305

Tuesday, September 29

10:45am-11:15amCoffee breakLind Hall 400
11:15am-12:15pmNew measures for characterizing nonlinear viscoelastic materials using large amplitude oscillatory shear (LAOS) deformationRandy H. Ewoldt (University of Minnesota)Lind Hall 305 PS

Wednesday, September 30

All DayNSF site visit
10:45am-11:15amCoffee breakLind Hall 400
11:15am-12:15pmTransport and collective dynamics in suspensions of swimming microorganismsMichael D. Graham (University of Wisconsin)Lind Hall 305 2009-2010Seminar
2:30pm-3:20pmTopics in the theory of the Navier-Stokes equationsVladimir Sverak (University of Minnesota)Lind Hall 305

Thursday, October 1

All DayNSF site visit
10:45am-11:15amCoffee breakLind Hall 400
Abstracts
Second chances
Abstract: Video (flv)
Second chances
Abstract: Video (flv)
Second chances
Abstract: No Abstract
James Adams (University of Surrey) Flowing Complex Fluids: Rheological measurements and constitutive modeling
Abstract: Experiments on solutions of entangled DNA[1], and polymers of high molecular weight dissolved in their oligomers[2] have produced some interesting rheological results. When subjected to shear flow simple fluids adopt a uniform shear rate. However, in these polymer solutions experimentalists have observed the formation of a more structured velocity distribution; regions of different shear rate on the order of 100 μ m form. To model this behaviour we analyse the transient behaviour of the diffusive Rolie-Poly model, a modern polymer constitutive equation, and incorporate a Newtonian solvent. The model parameters are chosen so that the constitutive model is monotonic. Numerical solution of this model in 1 spatial dimension shows that for certain parameter values inhomogeneous flow can develop during the transient, which then reverts to homogeneous flow in the long time limit. To understand this behaviour a linear stability analysis of spatial perturbations in the stress field is performed by expanding about the homogeneous transient. In particular the eigenvalues from the linear stability analysis are compared with numerical solution. [1] P. E. Boukany et al., Macromolecules 41, 2644, 2008.
[2] S. Ravindranath et al. Macromolecules 41, 2663, 2008.
Christopher Bemis (Whitebox Advisors) Robust portfolio optimization using a cross sectional factor model
Abstract: Active portfolio management has developed substantially since the formulation of the Capital Asset Pricing Model (CAPM). While the original methodology of portfolio optimization has been lauded, it is essentially an academic exercise, with practitioners eschewing the suggested weightings. There are myriad reasons for this: nonstationarity of data, insufficiency of modeling parameters, sensitivity of optimization to small perturbations, and assumption of uniform investor utility all indicate potential failures in the model. We present historical market data to exhibit the pitfalls outlined above. From this analysis, we proceed to examine robust portfolio construction methods. One in particular is provided by Goldfarb and Iyengar. We adapt their methodology to a cross sectional model for returns and examine the performance we achieve.
Edo S. Boek (Schlumberger Cambridge Research) Dynamics and rheology of wormlike micelles emerging from particulate computer simulations
Abstract: We study the large scale dynamics and rheology of semidilute wormlike micelles (WLMs) by coarse grained simulations. Specific mechanical properties of individual WLMs, such as the persistence length, diameter and elastic modulus, are determined from atomistic simulations, providing a link with the chemistry. We apply the method to a solution of erucyl bis (hydroxymethyl)methylammonium chloride (EHAC). Different scission energies lead to unentangled and entangled WLMs. We can explain the relaxation modulus of unentangled samples with a simple breakable Rouse chain theory. Increasing the shear rate leads to a decrease of the contour length and increase of the breaking rate. The stress is constant at intermediate shear rates. At high shear rate the stress is proportional to (shear rate)^(1/3), as confirmed by experiments [1]. [1] J. T. Padding, E.S Boek andW.J. Briels, J. Chem. Phys. , 074903 (2008).
Richard J. Braun (University of Delaware) Models for dynamics of the human tear film
Abstract: We study dynamics from models for the human tear film in one and two dimensional domains. The tear film is roughly a few microns thick over a domain on a centimeter scale; this separation of scales makes lubrication models desirable. Results on one-dimensional blinking domains are presnted for multiple blink cycles. Results on two-dimensional domains are presented for different boundary conditions. In all cases, the results are sensitive to the boundary conditions; this is intuitively satisfying since the seems to control the tear film from the boundary and its motion. Quantitative comparison with in vivo measurement will be given in some cases. Some discussion of tear film properties will also be given, and results for non-Newtonian models will be given as available, as well as a wish list for future data and models in this direction.
Wim Briels (Universiteit Twente) Simulations of mechanical failure in transient polymer networks
Abstract: We present a simulation model to describe the rheology of associative (telechelic) polymer networks, and solve some outstanding questions in the study of mechanical failure in polymeric fluids. The model uses a BD scheme, but accounts for transient forces arising from slow relaxations of the polymeric bridges in the network. In this way we account for structural memory occurring in our system.
Wesley R. Burghardt (Northwestern University) X-ray scattering studies of flow-induced alignment in model polymer nanocomposites
Abstract: The property enhancements associated with dispersion of nanoparticles in polymers will depend not only on the state of dispersion achieved during the synthesis or formulation of the nanocomposite, but also on the degree and direction of particle alignment induced during subsequent processing. Here we present data on flow-induced orientation in two classes of nanoparticle dispersions, based on multi-walled carbon nanotubes (MWNTs) and organically modified clay. Particles are dispersed in viscous but Newtonian matrices (uncured epoxy resin and oligomeric polybutene, respectively) to allow focus on the fundamentals of flow-induced particle orientation free from complications associated with polymer melt viscoelasticity. Small- and wide-angle x-ray scattering under shear are used to probe flow-induced anisotropy in the particle orientation distribution. Both samples show particle alignment increasing with shear rate. In dilute MWNT dispersions, flow-induced alignment is correlated with break-down of large aggregates. In more concentrated dispersion, unexpected rapid relaxation of flow-induced alignment suggests that some of the observed alignment stems from elastic distortion of entangled nanotubes within clusters. In the clay dispersions, attempts are made to explore the relationship between particle orientation and bulk rheological behavior. In both systems, we have explored the relation between anisotropy measures extracted from small- and wide-angle x-ray scattering, which probe fluid structure at different length scales.
Jason E. Butler (University of Florida) Rheology and dynamics of oscillated suspensions
Abstract: Non-colloidal suspensions of spheres undergoing oscillatory shearing flows demonstrate a range of unique, and even surprising, behaviors. Examples from rheological experiments include the existence of a non-monotonic dependence of the complex viscosity upon the strain amplitude and the observation of two distinct scales for the development of the rheology in time. Simulations of the oscillating suspensions predict the non-monotonic relationship between strain amplitude and the steady value of the complex viscosity while providing insights into the underlying microstructure that generates the macroscopic rheology observed in the experiments. Furthermore, the oscillatory rheology is related to the more general dynamics of suspensions within more complicated flows.
Paul Terence Callaghan (Victoria University of Wellington) Rheo-NMR of unusual shear banded flow in wormlike micelles
Abstract: In the study of shear banding phenomena in wormlike micelles, Rheo-NMR has proven of especial value, not only indicating the clear existence of shear bands, but also that they are associated with fluctuations, and sometimes, with molecular alignment. The subtlety of the correspondence (or lack of correspondence) between birefringence effects and shear banded flow has also been revealed. Recent measurements of shear-banded flow under Couette flow of the micellar system cetylpyridinium chloride and sodium salicylate (CPyCl/NaSal) indicate that shear banding fluctuations that are inconsistent with the usual lever rule picture. We have also used Rheo-NMR to investigate the flow and alignment properties of worm-like micelles formed by a 5% w/w solution of the BASF difunctional block copolymer non-ionic surfactant, Pluronic P105 in water along with 4.3% w/v 1-phenylethanol-d5. A variety of bizarre shear-banding and alignment behaviours are observed, along with both stable and fluctuating flows.
Michael E. Cates (University of Edinburgh) Mode coupling theory of colloid rheology
Abstract: The glass transition in quiescent colloidal suspensions is reasonably well accounted for by a mode coupling theory which treats the collective freezing of density fluctuations but neglects activated processes. In recent years we have extended this approach, with the aid of an exact nonequilibrium Green-Kubo formula, to address the nonlinear rheology of colloidal suspensions. The theory addresses the case of interacting Brownian particles with velocities biased by that of the local fluid flow (assumed homogeneous) thereby ignoring hydrodynamic interactions. The resulting constitutive equations are complicated but can be simplified for certain flows and/or by constructing a schematic model with similar features. The latter makes rheological prediction for general nonlinear flows a realistic goal, and allows the nontrivial yield behavior in the glass phase to be studied.
Eric Choate (University of North Carolina) Director angle anchoring conditions and the dynamic moduli of nematic liquid crystal polymers
Abstract: Joint work with M. Gregory Forest and Lili Ju. We break the orientational degeneracy of a nematic liquid crystal polymer system by applying strong anchoring conditions with an arbitrary director angle at the parallel plates in a shear cell. Then we apply a small amplitude oscillatory shear flow and predict the response of the storage and loss moduli with a tensor model with one-dimensional heterogeneity. We pay special attention to the role of the director angle anchoring conditions. For normal and tangential anchoring conditions, the model reduces to a form similar to the analytically solvable Leslie-Ericksen model. For oblique anchoring angles, we solve the system numerically, and we find a window of moderate frequencies where the storage modulus and viscosity are significantly larger than the corresponding Leslie-Ericksen predictions. We are able to approximate this very well with a linear superposition of the Leslie-Ericksen prediction and the corresponding monodomain prediction, and we find that for low frequencies and high frequencies the Leslie-Ericksen prediction is dominant, but for the window of moderate frequencies, the tensor order parameter contribution becomes dominant.
Annie Colin (Centre National de la Recherche Scientifique (CNRS)) Heterogeneous flows in complex fluids
Abstract: I will study the flow of complex fluids (emulsions , wormlike micelles solutions) in microfluidic devices. The velocity profiles are measured using Particles Imaging Velocimetry. Shear banded flows are evidenced in wormlike micelles solutions. The role of the confining and of the nature of the boundaries conditions will be adressed. These experiments will be analysed in the framework of non local rheology. Experimental data dealing with concentrated emulsion will be presented. In this case, no shear banding is evidenced eventhough some dynamical heterogeneities are pointed out. The size of the heterogeneities is measured using confocal imaging.
Phillipe Coussot (Centre National de la Recherche Scientifique (CNRS)) The secret life of yield stress fluids
Abstract: The situation of yield stress fluids in physics is very original: they borrow their properties partly to solids and partly to liquids, both material types which have strikingly different structures, and it is assumed that they can undergo a simple transition from one state to the other at a critical shear stress. This also implies difficulties for the mechanical description of their behavior: in the solid regime one usually follows the stress vs deformation while in the liquid regime one follows the stress vs shear rate. The experimental difficulties for determining the yield stress are inherent to this peculiar behaviour: one needs to identify the critical stress for which a flow occurs, which implies to detect a flow of a material with a viscosity tending towards infinity; as the flow curve tends to exhibit a plateau at low shear rates the uncertainty on measurements are obviously large and this is complicated by possible slight stress heterogeneities. Local measurements, i.e. inside the materials, are thus needed to determine the effective constitutive equation of the material. From MRI data we show that a certain class of materials appears to be simple yield stress fluids, except below a critical shear rate for which we cannot get any relevant data and which seems to be the “Bermuda Triangle” of pastes. For another class of materials the transition between the solid and the liquid regime is more abrupt: it occurs at a finite viscosity, so that no flow at a shear rate below a critical value can be observed in steady state. For these materials shear-banding in steady-state flows is the rule whatever the flow geometry. In addition this behaviour is associated with time-dependent properties: the shear-banding effect is obtained as a viscosity bifurcation in time. The behaviour of simple yield stress fluids (first class) in more complex geometries (extrusion, squeezing, object displacement, flow through a porous medium, etc) has received some attention in recent years and it is remarkable that the force vs velocity data are always well described by a model of the Herschel-Bulkley type, in analogy with their simple shear behavior. However the behaviour of yield stress fluids along a solid interface still constitutes a challenging field although of great interest for controlling various processes such as mud adhesion or drying, cream or gel coating, fouling deposits, welding of pottery pieces, adhesion of dental cements or glues, etc. We show some first observations with model materials which illustrate the complexity of this field and some unexplained results.
Georges F. Debrégeas (École Normale Supérieure) Quasi-static rheology of aqueous foams
Abstract: Aqueous foams, like other macroscopically divided materials, display intriguing rheological properties. The bubble-scale structure allows for the existence of frozen stresses within the material which can not spontaneously relax by thermal activation. Upon shearing, the system undergoes a series of plastic events which irreversibly modify this internal stress pattern. Reversely, the internal state of the material controls to a large extent its mechanical response to shear. To study this coupling, we have used a two-dimensionally confined aqueous foam along with a numerical simulation. Through image analysis of the film network, we can simultaneously probe the plastic flow and the frozen stress field dynamics under quasi-static shearing. We show that under oscillatory shear of moderate amplitude, the foam experiences a structural relaxation that leads to a decrease of the shear modulus and the emergence of normal stress differences. Upon continous shear, a shear-banding instability is observed, which coincides with the emergence of spatial heterogeneities in the internal stress field characteristics. The dynamics of the internal stress field can be interpreted using a simple statistical model.
Robert Deegan (University of Michigan) Vertical structures in shear thickening fluids
Abstract: The simplest models of matter posit a linear relationship between the stress and deformation, as for example in Hooke's law. However, many useful and important fluids (such as, shampoos, industrial slurries, geophysical fluids, polymeric melts) exhibit a nonlinear response to stress. In shear thickening fluids this nonlinear response manifests as an increase of the apparent viscosity with increasing shear rate. I will show that vibrated shear thickening fluids display a unique ability to maintain a vertically oriented free-surface despite the action of gravity. I will present my experimental results correlating this behavior with the rheological properties of the fluids, and my attempts to model the observed phenomena.
Jan Karel George Dhont (Forschungszentrum Jülich), Pavlik Lettinga (Forschungszentrum Jülich) Using time-resolved SANS to understand the flow behavior of PB-PEO wormlike micelles
Abstract: Dispersions of giant wormlike micelles of self-assembled Polybutadiene-poly(ethylene oxide) (2.5 kd:2.5 kd) diblock copolymers are known to undergo a phase transition around 3 to 10 w%. The response to shear flow around this concentration range is characterized by a considered shear thinning behavior. The object of this study was to obtain microscopic insight in the microscopic origin of shear thinning and the resulting instabilities. We first localized the (non-)equilibrium Isotropic (I)-Nematic (N) binodal, using the rheological response after shear-rate quenches. Using laser-Doppler velocimetry we confirmed that indeed close to I-N transition the shear thinning results in the formation of shear bands in the gradient direction. It is assumed that shear thinning is connected to the vicinity of the spinodal point where the rotational diffusion goes to zero. Therefore we used time-resolved Small Angle Neutron Scattering experiments in combination with Fourier-Transfer Rheology to probe the response of the Kuhn-segments subjecting the sample to an oscillatory shear field. Theory for ideal rods was used to connect the resulting stress response to the ordering response. With this approach we found not only the equilibrium spinodal point of this dispersion but also the microscopic origin of the shear thinning behavior.
Jan Karel George Dhont (Forschungszentrum Jülich), Pavlik Lettinga (Forschungszentrum Jülich) On the origin of vorticity banding
Abstract: Joint work with K. Kang (Forschungszentrum Jülich). We propose a possible scenario for the vorticity-banding instability on the basis of experiments on suspensions of long and thin colloidal rods (fd-virus particles). Vorticity banding of these suspensions is only observed inside the two-phase, paranematic-nematic coexistence region. Inhomogeneities that are formed due to initial paranematic-nematic phase separation are shown to drive the vorticity-banding transition, and stabilize the stationary vorticity-banded state. The kinetics of the banding transition depends on whether inhomogeneities are formed (after a shear-rate quench) due to paranematic-nematic spinodal decomposition or nucleation-and-growth. Particle-tracking experiments indicate that the vorticity bands are in weak, internal rolling motion. These and other observations indicate that normal stresses along the gradient direction are responsible for the vorticity-banding instability, and that these hoop stresses originate from the inhomogeneities. The mechanism underlying the vorticity banding transition is thus similar to the well-known elastic instability for polymers, where the role of polymers is now played by inhomogeneities that are formed due to paranematic-nematic phase separation.
Aaron Paul Rust Eberle (University of Delaware) Structure and rheology of nanoparticle gels and glasses
Abstract: Colloidal suspensions gel to a soft solid state when interparticle attractions increase sufficiently to overcome Brownian and stabilizing forces. Gelation at lower concentrations results from formation of a percolated, space-filling network, whereas at high concentrations, an attractive driven glass forms. At intermediate concentrations, phase separation, gel formation, percolation, and glass formation are all possible states leading to solid-like behavior and the exact mechanism of dynamic arrest is often unclear. In this work, we study the connection between the rheological properties and interparticle potential of a model thermoreversible gel and compare the results to the predictions of the new Krishnamurthy and Wagner model. Dynamic light scattering (DLS), fiber optic quasi-elastic light scattering (FOQELS), and small angle neutron scattering (SANS) are used to establish the single particle characteristics. Rheology, FOQELS, and SANS are used to study the interparticle potential, mechanisms of aggregation, and structure. The goal of this study is to test the ability of the new Krishnamurthy and Wagner model to predict the interparticle potential form bulk rheological measurements.
Randy H. Ewoldt (University of Minnesota) New measures for characterizing nonlinear viscoelastic materials using large amplitude oscillatory shear (LAOS) deformation
Abstract: Viscoelastic materials, such as biomaterials and non-Newtonian fluids, typically experience mechanical loading which evokes a nonlinear rheological response. Rheologically complex materials can provide novel functionality in biological and engineered systems. However, traditional characterization techniques are insufficient to appropriately describe nonlinear viscoelasticity. I will outline new measures which can be used to meaningfully describe the viscoelastic response of materials subjected to large amplitude oscillatory shear (LAOS) deformation. The new framework makes use of orthogonal Chebyshev polynomials and an appropriate choice of coordinate system in which to represent the data. The framework has been packaged into a distributable data analysis program to widen its use in both academic and industrial settings.
Marc-Antoine Fardin (Université de Paris VII (Denis Diderot)) Elastic instabilities in the flow of wormlike micelles
Abstract: Under shear, complex fluids often undergo instabilities leading to new flow patterns. The flow being usually inertialess, these instabilities are triggered by non-linear terms in the stress tensor itself. Shear-banding is such a flow-induced instability, observed in many systems of various microstructures from surfactant and polymer solutions, to emulsions, granular materials and foams. Above a critical shear-rate, a new fluid phase nucleates and the flow reorganizes into two macroscopic shear-bands of different viscosities coexisting in the velocity gradient direction. In a recent study performed in Taylor-Couette geometry, we showed that the flat interface between bands is unstable with respect to wavevectors along the vorticity direction. This interfacial instability is associated with the reorganization of the flow into Taylor-like vortices. Here, we attempt to connect this complex behaviour to the elastic instability occurring in dilute polymer solutions. In the latter case, the non-linear elastic term in the stress tensor has been shown to drive the flow instability, leading to the formation of Taylor-like vortices with patterns evolving towards turbulence when increasing shear rate. We propose a scenario where the induced fluid band undergoes an elastic instability. In the coexistence regime, the viscous phase act as a soft boundary and the instability leads to the formation of vortices mainly localized in the fluid band. For shear-rates above the coexistence regime, the boundary changes to a hard wall, increasing the threshold for the instability. The stability of the induced phase is then recovered. When the control parameter is further increased the flow becomes unstable again, leading to patterns reminiscent of elastic turbulence.
Suzanne M. Fielding (University of Durham) Shear banding in complex fluids and biologically active suspensions
Abstract: I will summarise some recent progress modelling shear banding in complex fluids, focussing particularly on the following topics: bulk and interfacial instabilities that lead to complex dynamics of the bands; vorticity banding; and 3D roll-like flows. Time permitting, I will also discuss a novel kind of shear banding that has recently been predicted in biologically active suspensions.
Emmanouela Filippidi (New York University) Self-organised criticality in sheared suspensions
Abstract: We study the behavior of non-colloidal suspensions under slow periodic strain. They undergo a dynamical phase transition from an active fluctuating state to an absorbing steady state. Starting from a random initial configuration, the system finds its staedy state via self-organisation. In the case of density-mismatched particles, the competing forces of sedimentation and shear-induced diffusion drive the system to its critical state. The timescales and lengthscales of active particle clusters are explored via a model and exhibit power law behavior. Future research will try to measure them the clusters in the experiment.
Peter Fischer (Eidgenössische TH Zürich-Zentrum) Vorticity and velocity banding in shear thickening solutions of wormlike micelles
Abstract: Joint work with Vishweshwara Herle, Joachim Kohlbrecher, and Sebastien Manneville. An equimolar mixture of cetylpyridinium chloride and sodium salicylate exhibits pronounced shear thickening and vorticity bands (alternating transparent and turbid bands) in non-linear flow regime. Rheological, flow visualization and rheo-SALS studies indicate a stress driven mechanism for the development of shear bands. A combination of rheo-NMR and UVP shows that not only vorticity bands, but also radial bands coexist in this system. To access the microscopic structure in these bands, time-resolved SANS measurements are performed in a transparent Couette geometry. These triggered experiments show that the transparent and turbid bands are composed of different kinds of highly anisotropic structures. Analysis of the structure factor indicates that long wormlike micelles are strongly aligned in flow direction in the turbid state and this alignment is destroyed to some extent in the transparent state.
M. Gregory Forest (University of North Carolina) Uniquely biological challenges for rheology
Abstract: The goal of this lecture is to inform the audience of the types of challenges that arise, and open problems that remain, in a specific class of biological fluids: mucus. Mucus is prevalent in biology and its rheology is fundamental for: locomotion (e.g., of snails); flow transport (e.g., of mucosal layers in mammalian lungs); and controlling diffusive transport of invasive particles (e.g., in the nasal cavity, lung, and reproductive organs). Mucus varies dramatically across species, across populations, across organs, and in a single organ across disease states. The lecture will address challenges faced in the Virtual Lung Project at UNC for design of experiments, for data-based inference of constitutive parameters, and for development of direct simulation tools for lung biology and medical applications.
Michael D. Graham (University of Wisconsin) Rheological modeling from the mesoscopic point of view
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Michael D. Graham (University of Wisconsin) Rheological modeling from the mesoscopic point of view (continued)
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Michael D. Graham (University of Wisconsin) Transport and collective dynamics in suspensions of swimming microorganisms
Abstract: A suspension of swimming organisms is an example of an active complex fluid. At the global scale, it has been suggested that swimming organisms such as krill can alter mixing in the oceans. At the laboratory scale, experiments with suspensions of swimming cells have revealed characteristic swirls and jets much larger than a single cell, as well as increased effective diffusivity of tracer particles. This enhanced diffusivity may have important consequences for how cells reach nutrients, as it indicates that the very act of swimming toward nutrients alters their distribution. The enhanced diffusivity has also been proposed as a scheme to improve transport in microfluidic devices and might be exploited in microfluidic cell culture of motile organisms or cells. The feedback between the motion of swimming particles and the fluid flow generated by that motion is thus very important, but is as yet poorly understood. In this presentation we describe theory and simulations of hydrodynamically interacting microorganisms that shed some light on the observations. In the dilute limit, simple arguments reveal the dependence of swimmer and tracer velocities and diffusivities on concentration. As concentration increases, we show that cases exist in which the swimming motion generates dramatically enhanced transport in the fluid. This transport is coupled to the existence of long-range correlations of the fluid motion. Furthermore, the mode of swimming matters in a qualitative way: microorganisms pushed from behind by their flagella are predicted to exhibit enhanced transport and long-range correlations, while those pulled from the front are not. A physical argument supported by a mean field theory sheds light on the origin of these effects. These results imply that different types of swimmers have very different effects on the transport of nutrients or chemoattractants in their environment; this observation may be related to the evolution of different modes of swimming.
Richard S. Graham (University of Nottingham), Peter D. Olmsted (University of Leeds) Kinetic Monte Carlo simulations of flow-induced nucleation in polymer melts
Abstract: We derive a kinetic Monte Carlo algorithm to simulate flow-induced nucleation in polymer melts. The crystallisation kinetics are modified by both stretching and orientation of the amorphous chains under flow, which is modelled by a recent non-linear tube theory. Rotation of the crystallites under flow is modelled by a simultaneous Brownian dynamics simulation. Our kinetic Monte Carlo approach is highly efficient at simulating nucleation and is tractable even at low under-cooling. The simulations predict enhanced nucleation under both transient and steady state shear. Furthermore the model predicts the growth of shish-like elongated nuclei for sufficiently fast flows, which grow by a purely kinetic mechanism. A comparison with experimentally observed nucleation rates during steady shear flow is also presented.
Thomas C. Hagen (University of Memphis) Localized Jeffery-Hamel flows of viscoelastic fluids
Abstract: Joint work with Jonathan D. Evans (University of Bath). The steady planar sink flow through a converging channel is considered for the upper convected Maxwell (UCM) and Oldroyd-B fluids. The local asymptotic structure near the wedge apex exhibits an outer core flow region together with thin elastic boundary layers at the wedge walls. A class of similarity solutions is described for the outer core flow in which the streamlines are straight lines, giving rise to stress and velocity singularities. These solutions are matched to wall boundary layer equations which recover viscometric behavior. The local solutions as described permit a wide variety of external flows from the far-field region and generalize the classical Newtonian case of Jeffery-Hamel flow.
Yunkyong Hyon (University of Minnesota) A macroscopic closure approximation to the micro-macro FENE model for polymeric materials
Abstract: We present an enhanced moment-closure approximation to the finite- extensible-nonlinear-elastic (FENE) models of polymeric fluids. This new moment-closure method involves the perturbation of the equilibrium probability distribution function (PDF), which takes into account of the drastic split into two spikes and centralized behavior under the large macroscopic flow effects. The resulting macroscopic system includes the moment-closure equations, the momentum (force balance) equations, as well as an auxiliary equation representing implicitly the dynamics of the spikes for the microscopic configurations.
Ross Nicholas Ingram (University of Pittsburgh) The Brinkman model for fast, viscous, and turbulent flows in porous media
Abstract: We consider a finite element method for the nonlinear Brinkman equation for modeling fast, viscous (possibly turbulent) fluid flow in porous media. Application areas include gaseous fluid flow in pebble bed nuclear reactors and wind sweeping across a wind farm. The Brinkman equations can be applied in two ways. The first perspective is to apply Brinkman as a porous media model, like Darcy’s equation, on a homogenized domain. The second is to apply Brinkman as a penalized Navier-Stokes equation (NSE), letting the Brinkman viscosity and inverse of the permeability tend to zero in the solid obstacles embedded in the problem domain. We derive a finite element formulation for non-generic constraints: non-homogeneous Dirichlet boundary conditions and non-solenoidal velocity (allowing for sources/sinks in a porous medium). Coupling between these two conditions makes even existence of solutions subtle (noting the Brinkman model contains the same nonlinearity as NSE). We provide conditions for stability, existence and uniqueness of solutions as well as pseudo-skew-symmetrization of the discrete, nonlinear convective term required for analysis of discrete, non-solenoidal Brinkman problem.
Ravi Prakash Jagadeeshan (Monash University) Micro and macro in the dynamics of dilute polymer solutions
Abstract: Recent developments in dilute polymer solution rheology are reviewed, and placed within the context of the general goals of predicting the complex flow of complex fluids. In particular, the interplay between the use of polymer kinetic theory and continuum mechanics to advance the microscopic and the macroscopic description, respectively, of dilute polymer solution rheology is delineated. The insight that can be gained into the origins of the high Weissenberg number problem through an analysis of the configurational changes undergone by a single molecule at various locations in the flow domain is discussed in the context of flow around a cylinder confined between flat plates. The significant role played by hydrodynamic interactions as the source of much of the richness of the observed rheological behaviour of dilute polymer solutions is highlighted, and the methods by which this phenomenon can be incorporated into a macroscopic description through the use of closure approximations and multiscale simulations is discussed.
Ravi Prakash Jagadeeshan (Monash University) Viscoelastic flow in a two-dimensional collapsible channel
Abstract: The effect of viscoelasticity on flow in a two-dimensional collapsible channel has been studied numerically. This geometry has some bearing to blood flow in a compliant blood vessel. Three different viscoelastic fluid models have been considered - the Oldroyd-B, the FENE-P and Owens’ model for blood [1], along with a zero thickness membrane model with constant tension for the collapsible wall [2]. The rheological behaviour of the viscoelastic fluids is described in terms of a conformation tensor model. The mesh equation and transport equations are discretized by using the DEVSS-TG/SUPG mixed finite element method [3]. The shape of the collapsible membrane, and the pressure, stress, velocity, and conformation tensor fields predicted by the different models is compared with the predictions of a Newtonian liquid. The existence of a limiting Weissenberg number beyond which computations fail is demonstrated for each of the viscoelastic fluids, and the dependence of the limiting Weissenberg number on the various model parameters is examined. Predictions for the different viscoelastic fluids differ significantly from each other, with the key factor being the extent of shear thinning predicted by the individual models. References: 1. R. G. Owens, J. Non-Newtonian Fluid Mech. 140, 57-70 (2006). 2. X. Y. Luo and T. J. Pedley, J. Fluids and Structures 9, 149-174 (1995). 3. M. Bajaj, J. R. Prakash and M. Pasquali, J. Non-Newtonian Fluid Mech. 145, 137-156 (2007).
Lijian Jiang (University of Minnesota) Mixed multiscale finite element methods using approximate global information and their applications in heterogeneous porous media
Abstract: We propose a framework of mixed MsFEMs using approximate global information based on partial upscaling. A requirement for partial homogenization/upscaling is to capture long-range (non-local) effects present in the fine-scale solution, while homogenizing some of the smallest scales. The local information at these smallest scales is captured in the computation of basis functions. Thus, the proposed approach allows us to avoid the computations at the scales that can be homogenized. This results to coarser problems for the computation of global fields. The mixed MsFEMs are able to improve accuracy significantly compared to local mixed MsFEMs. The mixeds MsFEMs can work efficiently for the problems with non-separable hierarchical scales. Analysis is given for the proposed methods. We show the applications of the mixed MsFEMs to deterministic porous media and stochastic porous media.
Hyunwoo Kim (University of Minnesota) Processing, morphology and properties of graphene reinforced polymer nanocomposites
Abstract: A unique combination of excellent electrical, thermal and mechanical properties has made graphene a multi-functional reinforcement for polymers. Exfoliated carbon sheets can be obtained from graphite oxide (GO) via either rapid pyrolysis (functionalized graphene sheets, FGS) or chemical modification (isocyanate treated graphite oxide, iGO). Solvent-based blending led to better dispersion of FGS in thermoplastic polyurethane than melt processing. Polyurethane became electrically conductive at even less than 0.5 wt% of FGS. Up to 10 fold increase in tensile stiffness and 90% decrease in nitrogen permeation of TPU were also observed with only 3 wt% of iGO implying high aspect ratio of exfoliated platelets. Dispersion of melt compounded graphite and FGS in poly(ethylene-2,6-naphthalate) was characterized with electron microscopy, X-ray scattering, melt rheology and solid property measurements. Unlike graphite, dispersion of FGS quantified from different routes spreads over a wide range due to structural irregularity and simplified assumptions for composite property modeling. For polycarbonate, flow-induced orientation reduced property gains by graphene dispersion, while quiescent-state annealing restored rigidity and electrical conductivity of the composites. Micro-structural evolution of FGS in polystyrene through annealing was monitored using melt-state rheological and dielectric measurements. Graphene-based polymer nanocomposites can be a new versatile soft material with numerous benefits.
Daniel J. Klingenberg (University of Wisconsin) Magnetorheology: Measurements, mechanisms and modeling
Abstract: Magnetorheological (MR) fluids are suspensions of small particles whose apparent rheological properties can be altered dramatically by applying a magnetic field. For example, magnetic flux densities of the order of 1 Tesla can induce a yield stress of the order of 100 kPa in an otherwise essentially Newtonian fluid. After a brief introduction to magnetorheology, including a few of the more common applications, four vignettes of experimental observations and resulting modeling challenges will be presented. In the first vignette, transients in shear flow rheology observed for large applied magnetic field strengths are addressed. These transients are associated with the formation of lamellae within the suspension, whose dynamics can be modeled at the particulate or continuum levels. In the second vignette, unexpectedly large yield stresses observed for suspensions with bidisperse particle size distributions are described. Particle-level modeling reveals the mechanism, but predicting the magnitude of the enhancement remains a challenge. The third vignette examines effects of friction, which only appear at large concentrations. Observations are similar to jamming transitions observed in similar systems. The last vignette examines a surprising enhancement caused by replacing magnetizable particles with nonmagnetizable particles in MR fluids.
Ronald G. Larson (University of Michigan) How well does the “standard” tube model for polymer dynamics work?
Abstract: Using concepts developed over the years by de Gennes, Doi, Edwards, Marrucci, Rubinstein, McLeish, Milner, and others, a kind of "standard model" for entangled polymer relaxation and rheology has been developed, which, like the "standard model" of high-energy physics, has a number of ad hoc assumptions and fitting parameters. The “standard model” of polymer relaxation is based on a phenomenological "tube" surrounding each polymer chain that represents the effect on that chain of non-crossability constraints imposed by surrounding chains. As a result of its confinement to the tube, the chain relaxes by reptation – or sliding along the tube, accordion-like fluctuations of the chain within the tube, and movement of, or dilation of, the tube due to motion of the surrounding chains creating the tube-like region. These ingredients have been generalized into algorithms for the prediction of linear rheology of arbitrary mixtures of linear and long-chain-branched polymers; these algorithms have a number of phenomenological parameters and ad hoc assumptions. An increasing body of experimental data on “well characterized linear and branched polymers” allows these theories to be tested in increasing detail. Here we describe the successes and failures of the “standard” model and discuss new molecular dynamics simulations and more refined experiments that might help the field transcend the limitations of the “standard model.
L. Gary Leal (University of California, Santa Barbara) Stress relaxation of comb polymers
Abstract: Joint work with Keith M. Kirkwood and Dimitris Vlassopoulos. In this presentation, we consider stress relaxation of comb polymers in both the linear and non-linear deformation regimes. In this poster, we focus primarily on the linear viscoelastic response and on the relaxation from a step shear strain for a set of comb polymers that have short branches, ranging from two Me to smaller values less than the entanglement molecular weight.
Sandra Lerouge (Université de Paris VII (Denis Diderot)) Dynamics of the shear banding flow in giant micelles
Abstract: Under shear, complex fluids often undergo instabilities leading to new flow patterns. Shear-banding is such a flow-induced instability, observed in many systems of various microstructures from surfactants and polymer solutions, to liquid crystal polymers, emulsions, granular materials and foams. It results from the coupling between the flow and the mesoscopic architecture of the system. The flow changes the structure of the fluid that feeds back on the flow itself. A spectacular consequence is a reorganization of the flow into two macroscopic shear-bands of different viscosities coexisting in the velocity gradient direction. In this scenario, the flow is supposed to be purely one-dimensional. Using flow visualizations in Couette geometry, we demonstrate, for a system of giant micelles that, in contrast with this classical picture, the banded state is unstable and evolves towards a three-dimensional flow. We show that vortices stacked along the vorticity direction develop concomitantly with interfacial undulations. These cellular structures are mainly localized in the induced band and their dynamics is fully correlated to that of the interface. As the control parameter increases, we observe a transition from a steady vortex flow to a state where pairs of vortices are continuoulsy created and destroyed. Normal stress effects are discussed as potential mechanisms driving the three-dimensional flow.
Alexei E. Likhtman (University of Reading) Hierarchy of models for entangled polymers
Abstract: I will briefly review multiscale approach to modelling of entangled polymers, which includes molecular dynamics (MD), single chain stochastic models (slip-springs) and the tube model. After that I will concentrate on the link between many chain (MD) and single chain models. I will report results from molecular dynamics simulations on stress relaxation and show the detailed comparison with slip-spring model. In the second part of the talk I will turn to the issue of microscopic definition of entanglement in molecular dynamics. We propose to define entanglement as a long-lived contact between mean paths of the two chains. Using this definition, we present empirical evidence and statistical properties of such entanglements, and discuss the implications for the tube theory and the slip-spring model.
Carlos R. López Barrón (University of Minnesota) 3D-Imaging of cocontinuous blends
Abstract: Geometrical parameters of the interface of a polymer blend with cocontinuous structure were obtained from differential geometry of 3D images. Fluorescently labeled polystyrene (FLPS) and styrene-acrylonitrile copolymer (SAN) were imaged with laser scanning confocal microscopy (LSCM). Images were analyzed for time evolution of interfacial area, curvature and curvature distributions. The coarsening kinetics is dominated by hydrodynamics which explain the initial linear growth of the microstructure. A slowing down of the coarsening at later times can be explained by the decrease of the interface curvature which is proportional to the coarsening driving force, i.e. the interfacial energy. The curvature distributions reveal the type of interface in the blend. For the 50/50 blends the distribution of the Gaussian curvature show mainly negative values, indicating an anticlastic surface, characteristic of bicontinuous structures. The distributions of the mean curvature are symmetrical and centered in zero at any time, indicating that the surface is evolving through the minimal energy path.
Christopher Macosko (University of Minnesota) Understanding silly putty, snail slime and other funny fluids
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Christopher Macosko (University of Minnesota) Understanding silly putty, snail slime and other funny fluids (continued)
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Kara Lee Maki (University of Minnesota) Human tear film dynamics on an eye-shaped domain
Abstract: Every time we blink a thin multilayer film forms on the front of the eye essential for both health and optical quality. Explaining the dynamics of this film in healthy and unhealthy eyes is an important first step towards effectively managing syndromes such as dry eye. Using lubrication theory, we model the evolution of the tear film during relaxation (after a blink). The highly nonlinear governing equation is solved on an overset grid by a method of lines in the Overture framework. Our simulations show sensitivity in the flow around the boundary to the choice of the flux boundary condition and to gravitational effects. Furthermore, the simulations capture some experimental observations.
Gareth Huw Mckinley (Massachusetts Institute of Technology) Constitutive modeling of the inhomogeneous response in steady and transient flows of entangled/micellar solutions
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Thomas Joseph Ober (Massachusetts Institute of Technology) Measurements of flow induced birefringence of complex fluids undergoing high rate deformations in microscale geometries
Abstract: Surfactant solutions make up a unique class of complex fluids, offering a wide variety of rheological behavior, e.g. shear banding, which may be tailored for a particular application. Within this class of solutions, micellar solutions, being composed of amphiphilic molecular chains, are representative of many consumer products, find use in advanced oil recovery, exhibit turbulent drag reduction, and they constitute an archetypal fluid for the study of flows in small-scale biological devices and porous media. The present understanding of the flow behavior of these micellar solutions is incomplete and to that end much experimental works is required in order to calibrate and improve current constitutive models of their rheological behavior. Of particular interest is the study of these fluids under high rate deformations (104-105 s-1) (Pipe et al. 2008), representative of flows in ink jet printers and lab on a chip experiments. Such high rates can be unattainable with conventional rheometers, but they are readily achievable in microscale geometries. Here, we present measurements of flow-induced birefringence (FIB) with micro particle image velocimetry (µ-PIV) measurements of micellar solutions undergoing both extensional and shear deformations at the microscale. We describe a novel birefringence microscopy system, which is capable of making time-resolved full-field measurements of the local extinction angle and retardance in a microfluidic device, providing for high-resolution tracking of the local microstructural evolution in a micellar solution undergoing strong deformation.
Peter D. Olmsted (University of Leeds) Does shear banding exist in polymer solutions?
Abstract: In 1975 Doi and Edwards predicted that entangled polymer melts and solutions can have a constitutive instability, signified by a decreasing stress for shear rates greater than the inverse of the reptation time. Early experiments did not support this, and more sophisticated theories were developed that incorporated Marrucci's idea (1996) of removing constraints by advection; this produced a monotonically increasing stress and thus stable constitutive behavior. Recent experiments have suggested that entangled polymer solutions may possess a constitutive instability after all, and have led some workers to question the validity of existing constitutive models. Based on this intense interest we have revisited some of the phenemology present in state of the art tube models for entangled polymers, and performed calculations that take into account the stress inhomogeneity inherent in rotating rheometers (cone and plate and cylindrical Couette). Using the Rolie-Poly model with an added solvent viscosity, we show that (1) instability and shear banding is captured within this simple class of models; (2) shear banding phenomena is observable for weakly stable fluids in flow geometries that impose a sufficiently inhomogeneous total shear stress; (3) transient phenomena can possess inhomogeneities that resemble shear banding, even for weakly stable fluids. Many of these results are model-independent.
Robert Gwyn Owens (University of Montreal) On the oscillatory tube flow of healthy human blood
Abstract: In this talk results of pressure gradient vs. volume flow rate calculations over a wide range of oscillatory frequencies for oscillatory tube flow of healthy human blood are performed using the non-homogeneous hemorheological model of Moyers-Gonzalez et al. [M.A. Moyers-Gonzalez, R.G. Owens, J. Fang, A non-homogeneous constitutive model for human blood. Part I. Model derivation and steady flow, J. Fluid Mech. 617 (2008) 327–354]. Results at low (2 Hz) oscillatory frequencies are shown to be in close conformity to the experimental data of Thurston [G.B. Thurston, The effects of frequency of oscillatory flow on the impedance of rigid, blood-filled tubes, Biorheology 13 (1976) 191-199] and the behaviour may be interpreted using a linear viscoelastic model. As the oscillatory frequencies increase a resonant frequency at which flow rate amplitude enhancement occurs is encountered. For frequencies greater than the resonant frequency the pressure gradient amplitude required to maintain a constant volume flow rate amplitude increases with the oscillatory frequency. For very high frequency oscillations we use a multiple time scales technique in conjunction with our non-homogeneous hemorheological model to solve for the leading order flow variables. It is found that the leading order expressions for the cell number density, average aggregate size and rr-component of elastic stress (i.e. that due to the red blood cells) are functions only of the radial coordinate r. The O(1) elastic shear stress is shown to be zero, so that, for sufficiently large values of the oscillatory frequency, the red cell contribution to the total shear stress tends to zero. Using our multiple time scales method it is also shown that the model behaves in the very high frequency regime like a generalized linear viscoelastic fluid, having a radially dependent complex viscosity. This allows us to explain the computed results using asymptotic expressions for the in phase and quadrature components of the pressure gradient in a linear viscoelastic fluid. In particular, we may predict the apparent complex viscosity of human blood in very high frequency oscillatory tube flow.
Wilson Poon (University of Edinburgh) Imaging the flow of concentrated suspensions
Abstract: I will review the methodology of imaging the flow of concentrated suspensions at single-particle and nearly-real-time resolution, and then discuss a number of surprising recent findings indicating that traditional constitutive equations applied to rheometric geometries may not tell the whole story about these supposedly well understood systems.
Sriram Ramaswamy (Indian Institute of Science) Films and drops of active fluid
Abstract: Biologically active fluids, such as bacterial suspensions or cytoskeletal extracts with molecular motors and ATP, are a source of intriguing problems in the physics of complex fluids. They are composed of particles that with internal machinery that take up energy from their surroundings and actively move the surrounding medium. My talk will review recent results on thin fluid films and drops of active fluids, and possibly the dynamics of a single stiff filament in an active film.
Michael Renardy (Virginia Polytechnic Institute and State University) Turning polymeric liquids into theorems
Abstract: No Abstract
Michael Renardy (Virginia Polytechnic Institute and State University) Turning polymeric liquids into theorems (continued)
Abstract: No Abstract
Yuriko Renardy (Virginia Polytechnic Institute and State University) Influence of viscoelasticity on drop deformation in shear
Abstract: Numerical simulations and experimental data are compared for the investigation of the influence of viscoelasticity on drop deformation in shear. A viscoelastic drop suspended in a Newtonian liquid, or a Newtonian drop suspended in a viscoelastic liquid, is sheared and investigated for transients, relaxation after cessation of shear flow, and step-up in shear rate. The Oldroyd-B and Giesekus constitutive models are implemented. Experimental data and numerical results are detailed in Verhulst et al., J. Non-Newtonian Fluid Mech. 156, 44-57 (2009).
Donald G. Saari (University of California, Irvine) Arnold family lecture – Chaotic elections: why don't we elect who voters really want?
Abstract: Minnesota voters can appreciate the many troubling events associated with elections. Far more serious things can go wrong in the voting process, but most of us do not know how to look for them. The speaker exposes the many surprising problems that can occur in elections and explains how they are uncovered through the power of mathematics. Expect to leave this lecture troubled about whether the "right person" won in a recent election of importance to you.
Jay D. Schieber (Illinois Institute of Technology) Application of the discrete slip-link model to bidisperse linear systems
Abstract: The discrete slip-link model (DSM) predicts that the contribution of chain sliding dynamics (SD) to the relaxation modulus has a shape significantly different from the contribution by constraint dynamics (CD) for monodisperse linear chains. These contributions are also different from what is predicted by tube models. However, the product of these two contributions are nearly identical for the two models, so no real difference is observable, at least for monodisperse systems. On the other hand, this observation suggests that tube models and slip-link models might yield different predictions for the observable relaxation modulus of bidisperse blends. Tube models essentially predict double reptation for blends. However, better agreement with data is obtained by using a phenomenological exponent of 2.2, which was proposed by Marrucci and also recommended by Rubinstein et al. and by Ruymbeke et al. The exponent is hypothesized to be an effect either of non-binary entanglements or tube dilation. We find that the DSM with binary entanglements predicts data at least as well as double reptation with the phenomenological exponent of 2.2. We conclude that the assumption of binary events for entanglements is sufficient.
Eric S. G. Shaqfeh (Stanford University) Part 1: The nonlinear dynamics of DNA/polymers in extensional dominated flows: Solutions and melts

Part 2: Margination of micro- and nano- particles in the flow through microchannels
Abstract: Part 1: In this part of the talk we will discuss the coil-stretch hysteresis in dilute polymer solutions for extension dominated flows, including three-dimensional mixed flows. We will then turn to entangled systems and discuss the role of slip-link simulations in elucidating the extensional behavior in concentrated solutions and melts. Part 2: Platelets are 7 times more likely to be at the periphery of the flow through microtubules than red blood cells above 35% hematocrit. The transport mechanism by which this occurs can be elucidated through dynamic simulation. In particular we will look at the effect of hematocrit and shear rate on these dynamics
Michael J. Solomon (University of Michigan) Viscoelasticity of bacterial biofilms probed by flexible microfluidic rheometry
Abstract: We discuss bacterial biofilms and the scope for describing their viscoelastic mechanical properties as a consequence of their underlying polymeric and multiphase morphology. Biofilms are the most prevalent phenotype of bacteria in nature. Biofilms form under conditions common in industry and in the body. They are structurally heterogeneous on multiple scales. We argue that the resolution of microscale mechanical properties is essential to fundamental understanding of the fate of biofilms in situations of flow, including the human circulatory system. Because of this need for microscale characterization, we developed the flexible microfluidic rheometer to characterize the elastic modulus and relaxation time of bacterial biofilms. The biofilms studied here are bacterial communities of Staphylococcus epidermidis and Klebsiella pneumoniae. The microfluidic device exploits the response of a flexible, deforming membrane to characterize the viscoelasticity of the test material. Attributes of the device are its simple fabrication and operation as well as its ability to accept biofilms grown at biologically relevant shear rates in the microfluidic environment. We find that the static and temporal responses of the valve membrane, as quantified by confocal microscopy, agree well with the viscoelastic properties of a model gellan gum as modeled by finite element simulation. Measurement of steady-state deformation yields both the linear and non-linear elastic response of the biofilms. We also report the transient response of the PDMS membrane coupled to the biofilm when the system is subjected to a stress relaxation experiment. We track the membrane deformation with the aim of extracting the viscoelastic relaxation time of the soft biological solid.
Kathleen J. Stebe (University of Pennsylvania) Oriented assembly of anisotropic particles at interfaces
Abstract: We study experimentally complex shaped partially wet particles on liquid-air interfaces. The interface deforms to satisfy the contact angle boundary conditions at the particle-liquid-air contact line. The deformations create excess liquid-air interface. When deformation fields between neighboring particles overlap, the excess area decreases as the particles approach each other. This creates a capillary attraction between the particles. Particle geometry influences the deformation field, creating preferred modes for particle assembly. Preliminary studies on the role of surfactants in altering these interactions will also be discussed.
Vladimir Sverak (University of Minnesota) Topics in the theory of the Navier-Stokes equations
Abstract: The course will cover certain selected topics in the theory of the Navier-Stokes equations. After a brief overview of the main issues of the general theory we will focus on problems in the theory of the steady-state solutions. There are many open problems concerning the steady-state solutions. These problems are presumably easier than the main open questions about the time-dependent equations. Nevertheless, some of them have remained unsolved since their first explicit formulation in the pioneering works of Jean Leray in the 1930s. There is a certain indirect similarity (or "duality") between the mathematical issues raised by these steady-state problems and the issues which come up in connection with the more well-known open problems about the time-dependent equations. In the lectures I hope to cover some of the important results about the steady-state solutions and discuss some of the open problems. The course will be accessible to postdocs and to graduate students with some knowledge of PDEs. For example, an introductory graduate PDE course should be a sufficient prerequisite.
Vladimir Sverak (University of Minnesota) Topics in the theory of the Navier-Stokes equations
Abstract: The course will cover certain selected topics in the theory of the Navier-Stokes equations. After a brief overview of the main issues of the general theory we will focus on problems in the theory of the steady-state solutions. There are many open problems concerning the steady-state solutions. These problems are presumably easier than the main open questions about the time-dependent equations. Nevertheless, some of them have remained unsolved since their first explicit formulation in the pioneering works of Jean Leray in the 1930s. There is a certain indirect similarity (or "duality") between the mathematical issues raised by these steady-state problems and the issues which come up in connection with the more well-known open problems about the time-dependent equations. In the lectures I hope to cover some of the important results about the steady-state solutions and discuss some of the open problems. The course will be accessible to postdocs and to graduate students with some knowledge of PDEs. For example, an introductory graduate PDE course should be a sufficient prerequisite.
Vladimir Sverak (University of Minnesota) Topics in the theory of the Navier-Stokes equations
Abstract: The course will cover certain selected topics in the theory of the Navier-Stokes equations. After a brief overview of the main issues of the general theory we will focus on problems in the theory of the steady-state solutions. There are many open problems concerning the steady-state solutions. These problems are presumably easier than the main open questions about the time-dependent equations. Nevertheless, some of them have remained unsolved since their first explicit formulation in the pioneering works of Jean Leray in the 1930s. There is a certain indirect similarity (or "duality") between the mathematical issues raised by these steady-state problems and the issues which come up in connection with the more well-known open problems about the time-dependent equations. In the lectures I hope to cover some of the important results about the steady-state solutions and discuss some of the open problems. The course will be accessible to postdocs and to graduate students with some knowledge of PDEs. For example, an introductory graduate PDE course should be a sufficient prerequisite.
Vladimir Sverak (University of Minnesota) Topics in the theory of the Navier-Stokes equations
Abstract: The course will cover certain selected topics in the theory of the Navier-Stokes equations. After a brief overview of the main issues of the general theory we will focus on problems in the theory of the steady-state solutions. There are many open problems concerning the steady-state solutions. These problems are presumably easier than the main open questions about the time-dependent equations. Nevertheless, some of them have remained unsolved since their first explicit formulation in the pioneering works of Jean Leray in the 1930s. There is a certain indirect similarity (or "duality") between the mathematical issues raised by these steady-state problems and the issues which come up in connection with the more well-known open problems about the time-dependent equations. In the lectures I hope to cover some of the important results about the steady-state solutions and discuss some of the open problems. The course will be accessible to postdocs and to graduate students with some knowledge of PDEs. For example, an introductory graduate PDE course should be a sufficient prerequisite.
Vladimir Sverak (University of Minnesota) Topics in the theory of the Navier-Stokes equations
Abstract: The course will cover certain selected topics in the theory of the Navier-Stokes equations. After a brief overview of the main issues of the general theory we will focus on problems in the theory of the steady-state solutions. There are many open problems concerning the steady-state solutions. These problems are presumably easier than the main open questions about the time-dependent equations. Nevertheless, some of them have remained unsolved since their first explicit formulation in the pioneering works of Jean Leray in the 1930s. There is a certain indirect similarity (or "duality") between the mathematical issues raised by these steady-state problems and the issues which come up in connection with the more well-known open problems about the time-dependent equations. In the lectures I hope to cover some of the important results about the steady-state solutions and discuss some of the open problems. The course will be accessible to postdocs and to graduate students with some knowledge of PDEs. For example, an introductory graduate PDE course should be a sufficient prerequisite.
Dawud H. Tan (University of Minnesota) Influence of viscosity and elasticity on the statistical properties of meltblown polymer fibers
Abstract: Melt blowing is a commercialized processing technique that produces a significant portion of nonwoven fiber products. It utilizes two streams of hot air to stretch an extruded polymer strand into a fiber, typically 2 μm in diameter. Our group has demonstrated the capability of producing defect-free fibers with an average diameter of roughly 400 nm using a lab-scale melt blowing device designed after a typical commercial instrument[1]. A systematic study of melt blowing of bidisperse polymeric blends with different rheological properties, obtained by mixing low and a high molecular weight polymer, will be presented. This work demonstrates the impact of melt viscosity and elasticity on the distribution of melt blown fiber diameters. [1] Ellison, C.J. et al. Polymer 2007, 48, 3306-3316.
Jean-Luc Thiffeault (University of Wisconsin) Stirring and mixing: Topology, optimization, and walls
Abstract: I review various aspects of current research, both experimental and theoretical, on stirring and mixing in fluids. Three main threads are followed: 1) How topological features influence mixing effectiveness; 2) How this leads to novel optimization methods; and 3) How one has to be mindful of wall effects, which can dramatically slow down mixing.
Norman J. Wagner (University of Delaware) Microstructure and rheology relationships for concentrated colloidal dispersions: Shear thickening fluids and their applications
Abstract: Measurements of the microstructure commensurate with the viscosity and normal stress differences in shearing colloidal suspensions provides an understanding of how to control the viscosity, shear thinning, and shear thickening rheological behavior typical of concentrated dispersions. In this presentation, I will review some of the experimental methods and key results concerning the micromechanics of colloidal suspension rheology. In particular, colloidal and nanoparticle dispersions can exhibit shear thickening, which is an active area of research with consequences in the materials and chemical industries, as well as an opportunity to engineer novel energy adsorbing materials. A fundamental understanding of shear thickening has been achieved through a combination of model system synthesis, rheological, rheo-optical and rheo-small angle neutron scattering (SANS) measurements, as well as simulation and theory. In particular, the shear-induced self-organization of “hydroclusters” (transient colloid concentration fluctuations) as predicted by Stokesian Dynamics simulations are measured and connected to the suspension rheology. The onset of shear thickening is demonstrated to be understood as a balance of convective, colloidal and hydrodynamic forces and their associated timescales. The limits of shear thickening behavior are also explored at extreme shear rates and stresses, where particle material properties come into play. Although many applications of concentrated suspensions are hindered by shear thickening behavior, novel materials have been developed around shear thickening fluids (STFs). Ballistic, stab and impact resistant flexible composite materials are synthesized from colloidal & nanoparticle shear thickening fluids for applications as protective materials. The rheological investigations and micromechanical modeling serve as a framework for the rational design of STF-based materials to meet specific performance requirements not easily achieved with more conventional materials, as will be discussed.
Visitors in Residence
James Adams University of Surrey 9/13/2009 - 9/19/2009
Nusret Balci University of Minnesota 9/1/2009 - 8/31/2010
Jennifer Beichman University of Michigan 9/1/2009 - 5/31/2010
Christopher Bemis Whitebox Advisors 9/11/2009 - 9/11/2009
Edo S. Boek Schlumberger Cambridge Research 9/13/2009 - 9/18/2009
Richard J. Braun University of Delaware 9/1/2009 - 12/20/2009
Michael P. Brenner Harvard University 9/30/2009 - 9/30/2009
Wim Briels Universiteit Twente 9/12/2009 - 9/19/2009
Wesley R. Burghardt Northwestern University 9/13/2009 - 9/18/2009
Jason E. Butler University of Florida 9/14/2009 - 9/18/2009
Maria-Carme T. Calderer University of Minnesota 9/1/2009 - 6/30/2010
Paul Terence Callaghan Victoria University of Wellington 9/13/2009 - 9/18/2009
Gunnar Carlsson Stanford University 9/30/2009 - 10/2/2009
Michael E. Cates University of Edinburgh 9/13/2009 - 9/18/2009
Chi Hin Chan University of Minnesota 9/1/2009 - 8/31/2010
Xianjin Chen University of Minnesota 9/1/2008 - 8/31/2010
Eric Choate University of North Carolina 9/13/2009 - 9/18/2009
Annie Colin Centre National de la Recherche Scientifique (CNRS) 9/12/2009 - 9/18/2009
Peter Constantin University of Chicago 9/13/2009 - 9/16/2009
L. Pamela Cook University of Delaware 9/6/2009 - 12/20/2009
Phillipe Coussot Centre National de la Recherche Scientifique (CNRS) 9/12/2009 - 9/18/2009
Michael Earl Cromer Jr University of Delaware 9/1/2009 - 12/31/2009
Georges F. Debrégeas École Normale Supérieure 9/13/2009 - 9/18/2009
Robert Deegan University of Michigan 9/13/2009 - 9/19/2009
Jan Karel George Dhont Forschungszentrum Jülich 9/12/2009 - 9/19/2009
Charles Doering University of Michigan 8/15/2009 - 6/15/2010
Aaron Paul Rust Eberle University of Delaware 9/13/2009 - 9/18/2009
Robert S. Eisenberg Rush University Medical Center 9/27/2009 - 9/29/2009
Randy H. Ewoldt University of Minnesota 9/1/2009 - 8/31/2010
Angbo Fang Hong Kong University of Science and Technology 9/10/2009 - 10/18/2009
Marc-Antoine Fardin Université de Paris VII (Denis Diderot) 9/13/2009 - 9/18/2009
Suzanne M. Fielding University of Durham 9/13/2009 - 9/18/2009
Emmanouela Filippidi New York University 9/13/2009 - 9/20/2009
David Finn Rose-Hulman Institute of Technology 9/1/2009 - 11/23/2009
Peter Fischer Eidgenössische TH Zürich-Zentrum 9/12/2009 - 9/19/2009
M. Gregory Forest University of North Carolina 9/11/2009 - 12/20/2009
Sandip Ghosal Northwestern University 9/21/2009 - 12/12/2009
Mihoko Giga University of Tokyo 9/10/2009 - 9/20/2009
Yoshikazu Giga University of Tokyo 9/10/2009 - 9/20/2009
Michael D. Graham University of Wisconsin 9/1/2009 - 12/22/2009
Richard S. Graham University of Nottingham 9/13/2009 - 9/18/2009
Thomas C. Hagen University of Memphis 9/1/2009 - 12/31/2009
Todd Hesla University of Minnesota 9/12/2009 - 9/13/2009
Christel Hohenegger New York University 9/13/2009 - 9/18/2009
Mary Ann Horn National Science Foundation 9/29/2009 - 10/6/2009
Thomas Hu Unilever 9/13/2009 - 9/16/2009
Yunkyong Hyon University of Minnesota 9/1/2008 - 8/31/2010
Ross Nicholas Ingram University of Pittsburgh 9/13/2009 - 9/18/2009
Mark Iwen University of Minnesota 9/1/2008 - 8/31/2010
Ravi Prakash Jagadeeshan Monash University 9/12/2009 - 9/19/2009
Paul Janmey University of Pennsylvania 9/15/2009 - 9/18/2009
Srividhya Jeyaraman University of Minnesota 9/1/2008 - 8/31/2010
Lijian Jiang University of Minnesota 9/10/2008 - 8/31/2010
Daniel D. Joseph University of Minnesota 9/14/2009 - 9/18/2009
Mihailo Jovanovic University of Minnesota 9/11/2009 - 6/10/2010
Hyejin Kim University of Minnesota 9/1/2009 - 8/31/2010
Hyunwoo Kim University of Minnesota 9/14/2009 - 9/18/2009
Daniel J. Klingenberg University of Wisconsin 9/13/2009 - 9/18/2009
Pawel Konieczny University of Minnesota 9/1/2009 - 8/31/2010
Satish Kumar University of Minnesota 9/14/2009 - 9/18/2009
Ronald G. Larson University of Michigan 9/12/2009 - 12/22/2009
L. Gary Leal University of California, Santa Barbara 9/13/2009 - 9/18/2009
Young-Ju Lee Rutgers University 9/11/2009 - 12/31/2009
Sandra Lerouge Université de Paris VII (Denis Diderot) 9/13/2009 - 9/18/2009
Pavlik Lettinga Forschungszentrum Jülich 9/12/2009 - 9/18/2009
Alex Levine University of California, Los Angeles 9/13/2009 - 9/18/2009
Marta Lewicka University of Minnesota 9/1/2009 - 6/30/2010
Yi Li University of Iowa 9/30/2009 - 10/1/2009
Yi Li Stevens Institute of Technology 9/16/2009 - 12/17/2009
Yongfeng Li University of Minnesota 9/1/2008 - 8/31/2010
Binh Lieu University of Minnesota 9/12/2009 - 9/18/2009
Alexei E. Likhtman University of Reading 9/13/2009 - 9/18/2009
Zhi (George) Lin University of Minnesota 9/1/2009 - 8/31/2010
Chun Liu University of Minnesota 9/1/2008 - 8/31/2010
Ellen K. Longmire University of Minnesota 9/1/2009 - 6/30/2010
Carlos R. López Barrón University of Minnesota 9/14/2009 - 9/18/2009
Christopher Macosko University of Minnesota 9/12/2009 - 9/18/2009
Yasunori Maekawa Kobe University 9/7/2009 - 3/1/2010
Krishnan Mahesh University of Minnesota 9/1/2009 - 6/30/2010
Kara Lee Maki University of Minnesota 9/1/2009 - 8/31/2010
Vasileios Maroulas University of Minnesota 9/1/2008 - 8/31/2010
Luca Martinetti University of Minnesota 9/14/2009 - 9/18/2009
Gareth Huw Mckinley Massachusetts Institute of Technology 9/13/2009 - 9/18/2009
Michael J. Miksis Northwestern University 9/13/2009 - 9/17/2009
Rashad Moarref University of Minnesota 9/12/2009 - 9/13/2009
Yoichiro Mori University of Minnesota 9/1/2009 - 6/30/2010
Susan J. Muller University of California, Berkeley 9/13/2009 - 9/18/2009
Monika Nitsche University of New Mexico 9/1/2009 - 12/22/2009
Thomas Joseph Ober Massachusetts Institute of Technology 9/11/2009 - 9/18/2009
David Olagunju University of Delaware 9/13/2009 - 9/18/2009
Peter D. Olmsted University of Leeds 9/13/2009 - 9/18/2009
Cecilia Ortiz-Duenas University of Minnesota 9/1/2009 - 8/31/2010
Hans G. Othmer University of Minnesota 9/1/2009 - 6/30/2010
Robert Gwyn Owens University of Montreal 9/15/2009 - 9/18/2009
Juan C Padrino University of Minnesota 9/12/2009 - 9/13/2009
Harald Pleiner Max Planck Institute for Polymer Research 9/12/2009 - 10/17/2009
Wilson Poon University of Edinburgh 9/13/2009 - 9/18/2009
Sriram Ramaswamy Indian Institute of Science 9/13/2009 - 9/18/2009
Michael Renardy Virginia Polytechnic Institute and State University 9/1/2009 - 12/15/2009
Yuriko Renardy Virginia Polytechnic Institute and State University 9/1/2009 - 12/20/2009
Juan Mario Restrepo University of Arizona 8/11/2009 - 6/15/2010
Donald Richards Pennsylvania State University 9/30/2009 - 10/5/2009
Donald G. Saari University of California, Irvine 9/21/2009 - 9/23/2009
Fadil Santosa University of Minnesota 7/1/2008 - 6/30/2010
Arnd Scheel University of Minnesota 9/1/2009 - 6/30/2010
Jay D. Schieber Illinois Institute of Technology 9/13/2009 - 9/18/2009
Robert Secor 3M 9/14/2009 - 9/18/2009
George R Sell University of Minnesota 9/1/2009 - 6/30/2010
Tsvetanka Sendova University of Minnesota 9/1/2008 - 8/31/2010
Gregory Seregin University of Oxford 9/20/2009 - 10/18/2009
Shuanglin Shao University of Minnesota 9/1/2009 - 8/31/2010
Eric S. G. Shaqfeh Stanford University 9/13/2009 - 9/17/2009
Michael J. Solomon University of Michigan 9/14/2009 - 9/17/2009
Daniel Spirn University of Minnesota 9/8/2009 - 6/1/2010
Kathleen J. Stebe University of Pennsylvania 9/13/2009 - 9/17/2009
Panagiotis Stinis University of Minnesota 9/1/2009 - 6/30/2010
Huan Sun Pennsylvania State University 8/16/2009 - 12/15/2009
Vladimir Sverak University of Minnesota 9/1/2009 - 6/30/2010
Keisuke Takasao Hokkaido University 9/11/2009 - 9/19/2009
Dawud H. Tan University of Minnesota 9/14/2009 - 9/18/2009
Mark Taylor Sandia National Laboratories 9/1/2009 - 12/22/2009
Jean-Luc Thiffeault University of Wisconsin 9/1/2009 - 6/30/2010
Yoshihiro Tonegawa Hokkaido University 9/11/2009 - 9/19/2009
Chad Michael Topaz Macalester College 9/1/2009 - 6/30/2010
Paula Andrea Vasquez University of Delaware 9/11/2009 - 9/16/2009
Norman J. Wagner University of Delaware 9/13/2009 - 9/16/2009
Changyou Wang University of Kentucky 9/1/2009 - 6/15/2010
Qi Wang University of South Carolina 9/8/2009 - 10/30/2009
Qixuan Wang University of Minnesota 9/13/2009 - 9/13/2009
Sijue Wu University of Michigan 9/1/2009 - 6/5/2010
Wei Xiong University of Minnesota 9/1/2008 - 8/31/2010
Xiaofeng Yang University of North Carolina 9/13/2009 - 9/18/2009
Tsuyoshi Yoneda University of Minnesota 9/4/2009 - 8/31/2010
Haijun Yu Purdue University 9/11/2009 - 9/19/2009
Weigang Zhong University of Minnesota 9/8/2008 - 8/31/2010
Chunfeng Zhou University of Minnesota 9/14/2009 - 9/18/2009
Legend: Postdoc or Industrial Postdoc Long-term Visitor

IMA Affiliates:
Arizona State University, Boeing, Corning Incorporated, ExxonMobil, Ford, General Motors, Georgia Institute of Technology, Honeywell, IBM, Indiana University, Iowa State University, Kent State University, Korea Advanced Institute of Science and Technology (KAIST), Lawrence Livermore National Laboratory, Lockheed Martin, Los Alamos National Laboratory, Medtronic, Michigan State University, Michigan Technological University, Microsoft Research, Mississippi State University, Motorola, Northern Illinois University, Ohio State University, Pennsylvania State University, Purdue University, Rice University, Rutgers University, Sandia National Laboratories, Schlumberger Cambridge Research, Schlumberger-Doll, Seoul National University, Siemens, Telcordia, Texas A & M University, University of Central Florida, University of Chicago, University of Cincinnati, University of Delaware, University of Houston, University of Illinois at Urbana-Champaign, University of Iowa, University of Kentucky, University of Maryland, University of Michigan, University of Minnesota, University of Notre Dame, University of Pittsburgh, University of Tennessee, University of Wisconsin, University of Wyoming, US Air Force Research Laboratory, Wayne State University, Worcester Polytechnic Institute