Complex interplay of structure and rheology in model ultrasoft polymeric spheres

Autori: D. Vlassopoulos, M. Kapnistos, R. Sigel, G. Fytas, T. Roovers, S. Pispas, N. Hadjichristidis
Presentato al: Southern Europe Conference on Rheology
Anno: 1999
Volume: 1
Issue: Unico
Casa Editrice: SIR-Cuen Napoli
Lingua: English


Abstract
We use recently synthesized model hyperstar polymers and giant diblock copolymer micelles in order to investigate the complex rheology of ideal liquid-ordered spheres characterized by tuned ultrasoft interactions. In particular, we focus on a reversible solidification transition and the viscosity-diffusion relationship.
Upon heating, concentrated solutions of hyperstar polymers, undergo a reversible liquid-solid transition. This unusual phenomenon is tentatively attributed to the trapping of the spheres in "cages" due to the swelling with temperature. On the other hand, the dynamic structure factor S(q,t) of the giant colloidal micelles is probed with photon correlation spectroscopy. We find that at the structural peak, the collective diffusion coefficient D(q) does not exhibit the anticipated slowing down, in sharp contrast to the respective behavior of hard colloidal spheres and diblock copolymer solutions, whereas it follows the same concentration dependence as the suspension’s zero-shear viscosity at concentrations below the crystallization transition, in analogy to the behavior of hard spheres.


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