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Mohan L.,University of Texas at Austin | Bonnecaze R.T.,University of Texas at Austin | Cloitre M.,CNRS Laboratory for Soft Matter & Chemistry
Physical Review Letters | Year: 2013

The long time persistence of mechanical stresses is a generic property of glassy materials. Here we identify the microscopic mechanisms that control internal stresses in highly concentrated suspensions of soft particles brought to rest from steady flow. The persistence of the asymmetric angular distortions which characterize the pair distribution function during flow is at the origin of the internal stresses. Their long time evolution is driven by in-cage rearrangements of the elastic contacts between particles. The trapped macroscopic stress is related to the solvent viscosity, particle elasticity and volume fraction through a universal scaling derived from simulations and experiments. © 2013 American Physical Society.

Smallenburg F.,University of Rome La Sapienza | Leibler L.,CNRS Laboratory for Soft Matter & Chemistry | Sciortino F.,University of Rome La Sapienza
Physical Review Letters | Year: 2013

Vitrimers - a recently invented new class of polymers - consist of covalent networks that can rearrange their topology via a bond shuffling mechanism, preserving the total number of network links. We introduce a patchy particle model whose dynamics directly mimic the bond exchange mechanism and reproduce the observed glass-forming ability. We calculate the free energy of this model in the limit of strong (chemical) bonds between the particles, both via the Wertheim thermodynamic perturbation theory and using computer simulations. The system exhibits an entropy-driven phase separation between a network phase and a dilute cluster gas, bringing new insight into the swelling behavior of vitrimers in solvents. © 2013 American Physical Society.

Nicolay R.,CNRS Laboratory for Soft Matter & Chemistry
Macromolecules | Year: 2012

A simple methodology to prepare well-defined polythiol copolymers by RAFT polymerization was developed. A methacrylate monomer carrying a S-alkyl-O-ethyl xanthate moiety as thiol protecting group was prepared in two high yield steps. Polythiols were obtained by copolymerizing the functional methacrylate and subsequent aminolysis of the protecting groups. Model reactions and polymerizations showed that the S-alkyl-O-ethyl dithiocarbonate functionality is fully compatible with the RAFT polymerization of methacrylates and did not induce any side reactions. Functionalization of polythiol copolymers was done via thiol-ene addition, Michael addition and thiol-disulfide exchange. Thiol deprotection and functionalization were done in one pot for Michael addition and thiol-disulfide exchange. A complete conversion of thiol groups was observed for all three types of reactions, exemplifying the potential of polythiol copolymers for the preparation of functional materials. © 2011 American Chemical Society.

Bonnecaze R.T.,University of Texas at Austin | Cloitre M.,CNRS Laboratory for Soft Matter & Chemistry
Advances in Polymer Science | Year: 2010

Soft glasses encompass a broad class of materials at the boundaries between polymers, granular dispersions, and colloidal glasses. Although they display a huge diversity of compositions and architectures, soft glasses share a common structure as well as generic static and flow properties. In this chapter, we show that the dense amorphous microstructure of soft glasses, combined with the existence of repulsive elastohydrodynamic interactions mediated by the solvent, lie at the heart of their behavior. These two basic ingredients are incorporated into a micromechanical model and a dynamic molecular-like simulation. Our theory successfully predicts near-equilibrium quantities such as the pair distribution function and shear moduli, the slip properties that are observed when soft glasses are sheared along solid surfaces, as well as the bulk shear rheology. These results, which connect properties at the particle scale to macroscopic behavior, provide predictive tools for the design of materials with a desired rheological response. © 2010 Springer-Verlag Berlin Heidelberg.

Vlassopoulos D.,Institute of Electronic Structure and Laser | Vlassopoulos D.,University of Crete | Cloitre M.,CNRS Laboratory for Soft Matter & Chemistry
Current Opinion in Colloid and Interface Science | Year: 2014

In the last two decades, advances in synthetic, experimental and modeling/simulation methodologies have considerably enhanced our understanding of colloidal suspension rheology and put the field at the forefront of soft matter research. Recent accomplishments include the ability to tailor the flow of colloidal materials via controlled changes of particle microstructure and interactions. Whereas hard sphere suspensions have been the most widely studied colloidal system, there is no richer type of particles than soft colloids in this respect. Yet, despite the remarkable progress in the field, many outstanding challenges remain in our quest to link particle microstructure to macroscopic properties and eventually design appropriate soft composites. Addressing them will provide the route towards novel responsive systems with hierarchical structures and multiple functionalities. Here we discuss the key structural and rheological parameters which determine the tunable rheology of dense soft deformable colloids. We restrict our discussion to non-crystallizing suspensions of spherical particles without electrostatic or enthalpic interactions. © 2014 Elsevier Ltd.

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