Thermoresponsive Binders –A Means to Control Silica Dispersion

Powder dispersibility is commonly enhanced with the use of chemical binders. Traditional binders are known to change filler-filler interactions by manipulating the binder chemical nature or concentration during the treatment process. On the other hand, responsive binders present an innovative alternative to control and improve dispersion phenomenon: agglomerates incorporating responsive polymers allow the adjustment of particle-particle and particle-fluid interactions by manipulating an external processing parameter. In this work, we have used thermoresponsive binders, namely the linear and crosslinked form of poly(N-isopropyl acrylamide) (PNIPAM) to identify changes in dispersion behavior of silica clusters driven by the experimental temperature. While for the linear binder, dispersion is enhanced at temperatures below LCST (lower critical solution temperature), the presence of the crosslinked binder changes dispersion behavior in an opposite way. These developments are attributed to modifications in the particle interfacial chemistry when linear PNIPAM is adsorbed onto the silica surface, and to the disruption of the agglomerate structure caused by the swelling/shrinking transition of the PNIPAM gel particles. A phenomenological model accounting for the temperature effect induced by the presence of PNIPAM hydrogels on agglomerate cohesivity and dispersion behavior has been developed. Predicted dispersion behavior at different temperatures shows good agreement with experimental data.