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We report results from experiments based on the spontaneous particle embedment technique to determine the surface compliance of poly(α-methylstyrene) (PαMS) for temperatures from room temperature to T g + 21 °C. Both submicrometer and nanometer diameter particles were investigated. Atomic force microscopy (AFM) measurements were used for the particle embedment determination, and the Lee and Radok (LR) model was applied to calculate the surface shear compliances using the embedment depth of the particles for the temperatures of interest. The adhesion force between the particles and the PαMS was used as the driving force for the embedment in the LR model calculation. Results were compared with macroscopic viscoelastic data for PαMS obtained from the literature and with new data from the present study. We observed surface softening for the PαMS in the temperature range from room temperature to T g – 21 °C. This was followed by a crossover to a surface mechanical response that was stiffer than the macroscopic material for temperatures from T g – 18 °C to T g + 21 °C. These novel findings were observed for both 199 and 60 nm diameter silica particles.

ABSTRACT:The thermal pressure coefficients of a neat, unfilled, epoxy resin and a 10 wt % POSS (polyhedral oligomeric silsesquioxane)-filled epoxy nanocomposite have been measured using a thick-walled tube method. It is found that just below the glass transition temperature the thermal pressure coefficient is $ 20% smaller for the polymer composite containing 10% POSS than for the neat, unfilled resin. The thermal expansion coefficient and thermal pressure coefficient of the uncured POSS itself are also reported.

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