LOW-FREQUENCY RAMAN-SCATTERING STUDY OF THE NANOSTRUCTURE OF PLASTICALLY DEFORMED POLYMER GLASSES

Plastic deformation of three amorphous polymers, such as poly(methyl m ethacrylate) (PMMA), poly(carbonate) (PC) and cross-linked PMMA, was i nvestigated by low frequency Raman scattering. The induced structure m odifications are found to differ in cross-linked and linear polymers. In the latter case, the deformation gives rise to a large scattering e xcess, maximum around 35 cm(-1), which is stronger with PC than with P MMA. The intensity of this excess depends on the inclination of the sh ear stress direction relative to the light polarization, thus indicati ng a significant anisotropy in the deformed amorphous structure. In th e frame of a non-continuous glassy structure model, these changes are interpreted by a partial orientation of macromolecular strands in nano metric, less cohesive zones of the matrix. In the case of a three-dime nsional polymeric network, the deformation occurs through a less local ized process, affecting the more cohesive regions. Similar arguments a re developed for specimens that were either plastically cycled or defo rmed at the glass transition temperature.