Dielectric Study on the Dynamic Heterogeneity of Binary Polymer Blends using Pressure as the Controlled Variable

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Recently it has been appreciated that, in several miscible binary polymer blends, the molecular motions of component polymers are heterogeneous, e.g. temperature dependences of each component dynamics are different. We think that the application of a pressure can reduce the distances between polymer segments and thus may induce more cooperative segmental motion between different polymer species. This will result in the increase of the dynamical homogeneity. Based on this view, we aim to clarify the degree of dynamic heterogeneity(homogeneity) as a function of pressure in this research project.Firstly, we constructed the dielectric cell in which the pressure can be controlled from 0.1MPa to 400MPa. Secondly, we tested the performance of the pressure cell. As a test sample we used a single component amorphous polymer, poly(buthylene oxide), which has the dipole moment parallel to the chain contour and thus global chain relaxation (so called normal mode process) is dielectrically observable. From this measurement we determined both the normal mode relaxation times τ_n and the segmental relaxation times τ_s. We found that both relaxation times have the same pressure dependence, i.e. log τ=log τ_0+b(P-P_0), where τ_0 is the relaxation time at atmospheric pressure, P_0 and b is the constant. This type of pressure dependence is already reported by several researchers. Therefore, we concluded that the applied pressure uniformly transmits to the sample specimen and dielectric measurements under the pressure can be done without problems.We studied dynamically heterogeneous behavior for several miscible blend systems under atmospheric pressure. However the systematic data for the pressure dependences of them have not yet been obtained. In the next step we are going to do dielectric measurement on several blend systems under the pressure and want to clarify the quantitative relationship between the pressure and the degree of dynamic heterogeneity.