Metastable States and Rheological Transitions in Soft Colloids

Dimitris Vlassopoulos

Soft colloids have emerged as a class of materials with very rich tunable rheology and ample applications.  We use star polymers as a representative model system whose softens can be tailored at molecular level by varying the number and size of arms.  We show their main properties, similarities with other systems and features that set them apart.  We then focus on kinetic transitions and discuss properties of star glasses and gels, their transitions induced by shear and thermodynamic (depletion) forces. We place special emphasis on the aging, the important of well-defined pre-shear protocols to study these systems and the change of size, and hence volume fraction, of the stars at high concentrations due to osmotic pressure.  Two particular aspects are addressed in more detail in this presentation: (i) the unusual aging kinetics in star glasses and gels; (ii) the transition from repulsive glass to gel and the consequences on rheological behavior.

Work performed in collaboration with D. Truzzolillo, B. Erwin (FORTH), M. Cloitre (ESPCI Paris Tech)  and M. Gauthier (Univ. of Waterloo) and supported by the EU (Comploids, Nanodirect, Softcomp).