Effect of affinity on gelation in highly size asymmetric bimodal suspensions

Abstract

We investigate the influence of inter-particle affinity on the microstructure and rheological behavior in the bimodal suspension systems. For this purpose, the model suspensions are designed by using two kinds of polystyrene beads (PS, size~530nm) as a large particle which are electrostatically stabilized and are different in surface properties only, while keeping unstable alumina coated silica (Al-silica, size~12nm) as a small particle. To change the affinity, hydrogen bonding is induced by modifying surface of PS as poly (vinyl pyrrolidone) (PVP). We investigate the influence of affinity between large and small particles by observing the changes in rheological properties and microstructure. Even with the same, the formation of Al-silica cluster which connects large particles is dominant when sulfate modified PS is used and the affinity between the particles is not strong. On the contrary, the Al-silica particles cover the surface of large particles rather than making bridges when PVP modified PS is used and the affinity is strong. The phase map which shows fluid-gel transition according to the composition of the suspension is also observed. The affinity is found to affect the shape of the phase map too. This research demonstrates how the differences in affinity between large and small particles affect the bimodal suspensions according to the surface properties of the particles, and provides an insight on the complex behavior of particulate fluids.