Scan-induced patterning and the glass transition in polymer films: Temperature and rate dependence of plastic deformation at the nanometer length scale

Environmental scanning force microscopy was used to investigate the temperature and rate dependence of the scan-induced formation of bundles in a thin polystyrene film. The spacing of the bundles increased monotonically with temperature, and this increase exhibited a cusp near the bulk glass transition temperature of polystyrene. The roughness of the patterns (which is proportional to the wave amplitude) and the rate of roughening with repeated raster scans both exhibited a maximum value at slightly higher temperatures. Thus, the temperature dependencies of the wavelength and the surface roughness are qualitatively and quantitatively different. Am Arrhenius model was used to describe the temperature and rate dependencies of the relaxations. The activation energies derived from these two independent analyses were found to be very similar to the value for the alpha relaxation in bulk samples.