An Application of Micro-Thermal Analysis to Polymer Blends

摘要

Micro-thermal analysis (micro-TA) is a new subsurface thermal analysis technology. The average of the DC signal is a function of the thermal conductivity, and the response to the AC modulation signal is a function of the thermal diffusivity of the subsurface. Using this technique, three images based on topography, thermal conduc- tivity, and thermal diffusivity are obtained simultaneously. Specific areas and domains in these images can then be characterized by simply positioning the probe and per- forming a localized thermal analysis experiment. The technique has been used to study the phase separation process in a 50:50 (by weight) polystyrene (PS)-poly(vinyl methyl ether) (PVME) blend and natural rubber-nitrile rubber blends. For these polymer blends, considerable contrast between phases is obtained, based on thermal conductiv- ity, whereas optical and electron microscopy would show them as being very similar . For example, it is difficult to image the morphology of natural and nitrile rubber blends by means of transmission electron microscopy, because of their similar chemical struc- tures. Micro-'l'A gives an excellent image of the morphology of these natural-nitrile rubber blends. This opens a new way for rubber industries to study morphologies of rubber-rubber blends in general. In the 50:50 PS-PVME blend, annealed at 125degC, spinodal decomposition occurred. With increasing time, the domain size and the glass transition temperature ofPS-rich domains increased, indicating that the concentration ofPVME in the PS-rich phases decreases. The results imply that micro-TA can be used to image the composition in the near-surface or surface regions in multicomponent materials, if the resolution is high enough.