Colloidal glass transition in unentangled polymer nanocomposite melts

Abstract

The linear and non-linear rheology of a high volume fraction particle filled unentangledpolymer melt is measured. The particles in the polymer melt behave like hard spheres asthe particle volume fraction is raised. At high volume fractions, the suspension develops aplateau elastic modulus. Over the frequency range of the elastic modulus plateau, theviscous modulus develops a minimum and a maximum. The frequencies of the two localextrema initially have critical power law scaling, suggesting the approach of a singular glasstransition. At higher volume fractions in excess of the glass transition, the viscous moduluscontinues to show a well defined minimum and a well defined maximum. The non-linearmoduli show a single perturbative yield point beyond which the suspension softens. Theyielding behavior of the nanocomposite is shown to be sensitive to the strainfrequency and the proximity of the strain frequency to the maximum frequencyfor the linear viscous modulus from linear rheology which characterizes thermalrelaxation of glassy particle clusters in the zero strain limit. The linear and non-linearmeasurements are compared against a recently developed mechanical theory for colloidalglasses.