Correlation of Polysiloxane Molecular Structure to Shear Thinning Power Law Exponent Using Elastohydrodynamic Film Thickness Measurements

Abstract

Siloxanebased polymers (polysiloxanes) are susceptible to temporary shearthinning that manifests as a reduction of elastohydrodynamic film thickness with increasing entrainment speed or effective shear rate. The departure from Newtonian film thickness can be predicted with the powerlaw exponent ns, an indicator of the severity of shearthinning in a polymeric fluid that is influenced by the macromolecular structure. In this paper, a combination of extant rheological and tribological models is applied to determine the powerlaw exponent of several polysiloxanes using film thickness measurements. Film thickness data at several temperatures and slidetoroll ratios are used to validate the methodology for several siloxanebased polymers with alkyl and aryl branches.