The role of polymer in dispersion stability and film formation of silica/PVA suspension

Film formation of particle/binder/solvent system is of importance in various applications to produce battery, display, electronic components and so on. Because dispersion stability is a crucial issue for defect-free final products, many attempts have been carried out to analyze and control the microstructure of the suspension. In this study, The effect of polymers on dispersion stability and film formation of particle/polymer suspension was investigated in terms of particle/polymer affinity, adsorption kinetics. Silica/poly(vinyl alcohol) suspension was used as a model suspension. Suspension microstructure and stress development during drying[1] were characterized and their relationship was investigated. The effect of particle/polymer affinity on microstructural change during drying of silica/PVA suspension was studied by changing pH from 1.5 to 9[2]. As shown in the inset of Figure 1, the amount of adsorption was measured to increase with decreasing pH, and the degree of flocculation in silica/PVA suspension became stronger with decreasing pH. However, through measurement of stress development during drying (Figure 1) and observation of film microstructure after drying (Figure 2), it was found that more strongly flocculated suspension became more dispersed and close-packed film after drying. In order to explain the structural change during drying, the following drying mechanism was suggested based on the evaluation of potential energy (Figure 3). As pH decreases, the adsorbed polymers could bridge the particles and lead to flocculated suspension before drying. As the solvent evaporates during drying, the adsorbed polymers introduce steric repulsion between approaching particles, leading to a change from flocculated to dispersed microstructure.