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Invited Speakers

Prof. Mike Cates, University of Cambridge (UK).

Bio: Mike is a member of the Department of Applied Mathematics and Theoretical Physics. He heads the Soft Matter research group. His current research interests include: flow of colloids, polymers, emulsions, gels and other soft materials; shear-thickening and rheology in dense suspensions; dynamics of soft glasses; flow of liquid crystals; general theories of active matter; cellular locomotion; phase ordering in active and passive systems; statistical mechanics of active particles; and numerous other topics.

Flow of Dense Suspensions: Protocols to Prevent Jamming

Abstract: The flow of very dense suspensions shows problematic features such as discontinous shear-thickening which can clog processing equipment. Such features are increasingly understood in terms of a (stress-dependent) contact friction between suspended particles. This understanding explains the
success of a empirical formulation strategy for increasing flowability by use of so-called 'emulsifiers'. It also suggests a second strategy based on modifying the process flow rather than the formulation, which
is to add a vibrational component that stops frictional contacts from building up. Numerical simulations show this to be effective only if the vibration is transverse to the main flow rather than along it. The behavior is partly explicable using the concept of an absorbing state transition created by the vibratory component which is weakly perturbed by the main flow. Prof. Michel Cloitre, Ecole Supérieure de Physique et Chimie Industrielles de la Ville de Paris (FR)

Bio: Michel Cloitre is research director at the Centre National de la Recherche Scientifique in France and is currently affiliated to the Soft Matter and Chemistry laboratory at ESPCI Paris. He develops a methodology at the interface between chemistry, physics, and mechanics to connect the macroscopic properties of materials to their structure and dynamics at the molecular scale. He is known for the advances he made on understanding and modeling the effect of flow on the structure and macroscopic behavior of colloidal glasses and composites, pastes and emulsions, physical gels, binary associative polymers based on reversible covalent bonds, and water-soluble polymers with complex architectures. Important applications studied in collaboration with industrial partners include liquid-liquid encapsulation, enhanced oil recovery and the development of hydrocolloids for water-borne formulations. He teaches undergraduate and graduate courses on soft matter, molecular rheology, and material design.

Microscopic design of soft colloidal materials

Abstract: At high concentration, dispersions of deformable particles such as emulsions, microgels, micelles and star polymers jam into glassy materials that behave as weak elastic solids at rest but yield and flow at high stresses. These materials are basic components of viscoplastic formulations used as high-performance coatings, solid inks, ceramic pastes, textured food, or personal care products. The packed amorphous microstructure of soft particle glasses lies at the heart of their rheological behavior. Individual particles are trapped in cages and can only move past one another appreciably if the local stress exceeds the strength of the contact interactions. Interestingly, chemistry offers a panel of strategies to tune the internal architecture of particles, the local elasticity, and the contact interactions, which generally involve elastic repulsion and attractions of different origins. We will review recent advances that bridge the gap between particle scale properties and macroscopic rheology, thereby opening new routes towards the rational design of soft colloidal materials. Prof. Fred C. MacKintosh, Rice University, Houston, TX (USA)

Bio: Fred MacKintosh received his PhD in Theoretical Physics from Princeton University. Following a postdoc at Exxon Corporate Research, he joined the Physics Department at the University of Michigan as Assistant, then Associate Professor. In 2001, Fred joined the Vrije Universiteit in Amsterdam as Professor of Theoretical Physics of Complex Systems. Since 2016, he has been the Abercrombie Professor of Chemical and Biomolecular Engineering at Rice University, as well as a member of the Center for Theoretical Biological Physics, with additional appointments in the Departments of Chemistry and Physics and Astronomy. His primary research interests include the physics of biopolymers and their networks, cell mechanics and non-equilibrium aspects of active and living soft matter.

Mechanical phase transitions and the rheology of stiff polymers

Abstract: The mechanics of cells and tissues are largely governed by scaffolds of filamentous proteins that make up the cytoskeleton, as well as extracellular matrices. The observed rheology of these systems is particularly rich in their nonlinear response. The constituent biopolymers are typically much more rigid to bending than synthetic polymers, which tends to make the rheology of biopolymer networks more challenging and subtle to understand. As we argue, the rheology of stiff polymer networks can be partly understood in terms of mechanical phase transitions, especially in the limit of highly rigid, athermal fibers. A classic example of a mechanical phase transition was identified by Maxwell for macroscopic engineering structures: networks of struts or springs exhibit a continuous, second-order phase transition at the isostatic point, where the number of constraints imposed by connectivity just equals the number of mechanical degrees of freedom. We will present recent theoretical predictions and experimental evidence for mechanical phase transitions and critical phenomena in biopolymer networks. We demonstrate quantitative agreement between predicted nonlinear rheology and the measured elastic response of collagen networks. We also show how critical fluctuations associated with a mechanical phase transition can lead to strong anomalies in the normal stress of such systems.
