Effect of Shell Architecture on the Static and Dynamic Properties of Polymer-Coated Particles in Solution

A quantitative comparison of the effect of the architecture of polymer grafts on the static and dynamic properties of polymer-functionalized colloidal systems in good solvents is presented. Polystyrene-coated silica particle brush model systems exhibiting identical hard core diameter but distinct polymer-shell architectures corresponding to the concentrated and intermediate brush regime were synthesized using atom transfer radical polymerization (ATRP) and studied using static and dynamic light scattering. Both particle systems conform to a core-shell-like form factor, and single self-diffusion is observed in the limit of dilute concentrations. Despite the significantly larger hydrodynamic radius of the intermediate brush particles, the onset of liquidlike structure formation is observed at about equal particle concentration for both systems, indicating the soft star-polymer-type interactions of intermediate brush particles. The comparison with the structure and the hydrodynamic factors of hard-sphere suspensions underlines the significant interpenetration of the grafted polymer chains for the particles in the intermediate brush regime. In particular, for semidilute concentrations the threshold concentration for graft-polymer interpenetration of dense particle brushes (evidenced by the emergence of a fast cooperative relaxation mode and a slow particle self-diffusion) is found to be increased by about an order of magnitude as compared to the intermediate brush analogue. The pronounced effect of the architecture of grafted polymer shells on the concentration dependence of the osmotic pressure and dynamic characteristics of particle suspensions illustrates the rich and hitherto unexplored parameter space that determines the organization of particles in suspension and provides insight into the origin Of Subtle effects related to polymer functionalization that have been observed previously in the crystallization of colloidal systems.