An application of micro-thermal analysis to polymer blends

Micro-thermal analysis (micro-TA) is a new subsurface thermal analysis tech nology. The average of the DC signal is a function of the thermal conductiv ity, and the response to the AC modulation signal is a function of the ther mal diffusivity of the subsurface. Using this technique, three images based on topography, thermal conductivity, and thermal diffusivity are obtained simultaneously. Specific areas and domains in these images can then be char acterized by simply positioning the probe and performing a localized therma l analysis experiment. The technique has been used to study the phase separ ation process in a 50:50 (by weight) polystyrene (PS)-poly(vinyl methyl eth er) (PVME) blend and natural rubber-nitrile rubber blends. For these polyme r blends, considerable contrast between phases is obtained, based on therma l conductivity, 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 micros copy, because of their similar chemical structures. Micro-TA gives an excel lent image of the morphology of these natural-nitrile rubber blends. This o pens a new way for rubber industries to study morphologies of rubber-rubber blends in general. In the 50:50 PS-PVME blend, annealed at 125 degreesC, s pinodal decomposition occurred. With increasing time, the domain size and t he glass transition temperature of PS-rich domains increased, indicating th at the concentration of PVME in the PS-rich phases decreases. The results i mply 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. (C) 2001 John Wiley & Sons, Inc.