(396d) Responsive Binders for Controlling Dispersion Behavior of Fine Particle Clusters

Fine particle clusters are frequently encountered in a wide range of important chemical, biotechnical, medical and materials processing applications including pharmaceutical, polymer, mining, and food technologies. Often, the processing goal is the dispersion of the agglomerate into smaller clusters (or if possible, into its constituent particles) and distribution of these finely divided units throughout the suspending medium. In other industries, the processing of powders aims to achieve an opposite goal, namely the consolidation of particles into agglomerates or the compaction of existing agglomerates into denser units. The same set of fundamental forces that govern dispersion processes also control the granulation processes. Dispersion occurs when the cohesive forces that hold the particle assemblies together are overcome by the hydrodynamic forces that tend to pull particles apart. Traditionally, dispersion has been controlled and enhanced by optimizing the factors that directly affect this counterbalance of forces. The focus of this study is based on a new approach to control dispersion though variables which are not directly related to the solid or dispersing fluid properties. This is achieved with the use of chemical systems that respond to external stimuli. Using this type of chemical systems as the particle surface modifier, it is possible to adjust the degree of interparticle interaction by changing the variable to which the additive is responsive. In particular, this study involves the use of silica powder treated with Poly(N-Isopropyl Acrylamide), PNIPAM, a thermo-responsive polymer. This study is aimed at evaluating whether changes in processing temperature lead to physical re-conformation of the PNIPAM chains altering the cohesion of the agglomerates and therefore, the mode and/or kinetics of the dispersion process. We found that while dispersion of hydrophilic silica powder seemed to be temperature independent, dispersion of hydrophobic silica agglomerates showed evidence of temperature dependence through changes in kinetics and mechanism of dispersion.