The effect of adsorption kinetics on film formation of silica/PVA suspension

Particle/binder/solvent systems are widely used in many applications and have long been studied. Understanding and controlling polymer adsorption in these complex material systems are important to achieve successful final performance. In this study, the effect of polymer adsorption on film formation and the relation between the microstructures of the suspension and film have been investigated by measuring the amount of polymer adsorption and the stress development during drying. In terms of mixing (or dispersion) time (t(m)), the adsorption amount (Gamma(PVA)), characteristic stress (sigma(ch)) and dried film density (rho) showed a similar behavior in the form of 1 - e(tm/tau) with a single characteristic time tau = 45 h, which implies that the drying process is determined by this single time constant. The porous and non-uniform microstructure of the dried film at short t(m) became close-packed and uniform with longer t(m). The polymer adsorption was found to play a key role in film formation as it introduces steric repulsion in suspension anti suppresses the flocculation during solvent evaporation. It was also pointed out that enough mixing time for the saturated polymer adsorption is critical to acquire the consolidated and uniform film microstructure. (C) 2009 Elsevier Inc. All rights reserved.