Strain controlled shear hardening behavior in suspensions of alumina spheres in a polydimethylsiloxane oligomer matrix

Abstract

AbstractAs a model system for thermal interface materials (TIMs), the complex rheological behavior of polydimethylsiloxane oligomer (oDMS)/alumina sphere particles (AlS) suspensions (i.e., oDMS/AlS) is investigated systematically in this work. Aluminum particles with 1 and 10 μm were used as fillers. Here, a surface treatment by using a silane coupling agent as found to be effective in improving the fluidity of the suspensions with small sized AlS particles. Peculiar large amplitude oscillatory shear (LAOS) results were observed for the suspensions that exhibited three or four responses (Hookean regime, shear softening, shear hardening and a second shear softening) depending on the surface properties of AlS particles. For the oDMS/AlS10 neat system, the width of the Hookean regime is determined by the shear stress () instead of the shear strain (), whereas it completely disappears in the oDMS/AlS10t system due to the increase potential energy between particles. Both critical stress and strain at the onset point for strain hardening decreased with the increase of particle concentration. Frequency dependent measurements illustrates that it is the critical strain instead of the stress that controls the shear hardening behavior. Average distance of neighboring particles is assumed to play a key role in the formation of hydroclusters.