Low-Temperature Features of the Micromechanical Properties of Polystyrene

The microindentation of thin polystyrene plates, which is an amorphous linear thermoplastic polymer with a glass transition temperature T-g approximate to 373 K, was carried out in the 77-295 K temperature range. A decrease in the temperature from 295 K to 140 K generated a two-fold linear increase in microhardness, which is in good agreement with the temperature dependence of the forced elasticity limit of polystyrene measured by other authors during uniaxial compression deformation. At temperatures of T = 77-140 K the local deformation of polystyrene was reversible: during heating to room temperature the impressions on the sample surface disappeared completely. Partial deformation reversibility was observed upon indentation in the temperature range of 140-190 K, but at indentation temperatures T > 190 K the impressions remained. The microstrain reversibility of polystyrene in nitrogen at, and close to, 77 K is due to the effect of the adsorption-active medium on the formation of crazes (fibrillar-porous nanostructures), the glass transition temperature of which is tens of degrees below that of bulk polymer.