Single Particle Motion of Hard-Sphere-Like Polymer Micronetwork Colloids Up to the Colloid Glass Transition

Abstract

Polymer micronetwork spheres swollen in a good solvent can be regarded as colloids which require no special stabilisation to avoid aggregation. Their interactions can be timed by changing the degree of internal crosslinking. The phase behaviour and the static structure factor demonstrate that crosslink density of 1:10 (inverse number of monomer units between crosslinks) is sufficient to achieve hard sphere behaviour. We designed a host-tracer system consisting of core-shell micronetwork spheres (core: polystyrene; shell: poly-t-butylacrylate) in a host of refractive-indexmatched poly-t-butylacrylate micronetwork colloids. Employing a crosslink density of 1:10 and tuning the polydispersity such that crystallisation is just avoided we are able to monitor the self-diffusion of a system with hard sphere interactions up to volume fractions close to the colloid glass transition by dynamic light scattering. In addition the long-time self-diffusion was measured with the forced Rayleigh scattering technique.

We compare the measured long-time self-diffusion coefficients with the predictions of theoretical concepts which differ in their treatment of hydrodynamic interactions. We find that mode coupling theory, neglecting hydrodynamic interactions, is able to describe our data only very close to ø _g . The theory of Medina-Noyola, where hydrodynamic interactions are assumed to directly affect only the short-time dynamics, seenis to work only up to moderately high volume fractions. In contrast, a new approach by Tokuya.ma and Oppenheim, where Hydrodynamic interactions are explicitly treated, is fully consistent with our results over the full volume fraction range.