Colloid aggregation arrested by caging within a polymer network

The aggregation of colloidal particles within the confines of a polymer network has been studied. An isorefractive covalently cross-linked polymer gel in dimethyl sulfoxide was formulated so that the multicomponent system that is the gel is essentially invisible to light scattering. The high dielectric solvent was chosen so that electrostatics could be used to control the state of aggregation of a colloid dispersed within the gel matrix. Smoluchowski's population balance equations were solved for the case where aggregates larger than the gel's mesh spacing are immobile. Light scattering intensities predicted from the evolution of the aggregate population were calculated. The observed asymptotic increase in scattering intensity is consistent with this model and indicates that the aggregation process becomes arrested by the spatial constraints imposed by the mesh of the polymer network. Essentially once the aggregates reach a certain size, they become caged within the mesh of the gel network and thus no longer aggregate. Evidence is also given that indicates that formulating for specific gel properties can lead to controlled final aggregate size.