Film formation of acrylic latices with varying concentrations of non-film-forming latex particles

We have employed ellipsometry and environmental SEM (ESEM) to determine the kinetics of film formation in mixtures of film-forming (FF) and non-film-forming (NFF) acrylic latices. We find that an increasing concentration of NFF latex leads to progressively larger voids. We have also found that minimizing the number of NFF-NFF particle contacts within the mixture results in a denser material. The rate of void closure during the early stages of film formation is enhanced by the presence of NFF latex particles, because the particles lead to a higher surface area that provides a stronger driving force for void closure. Despite this effect, a latex with a higher concentration of NFF particles takes longer to reach full density. We have applied the Mackenzie-Shuttleworth theory to our densification data and found a value for the viscosity of the FF latex that is consistent with the literature. In some cases, we see evidence for polymer viscosity changing with time, indicative of hydroplasticization. We find that our calculated viscosity of the FF latex decreases with increasing temperature and increases with the addition of 40 wt% NFF particles. We comment on the implications that this work has for the measurement of the critical pigment volume concentration.