Simultaneous dynamic mechanical and dielectric measurements on polymers

Abstract

A comparison of dielectric and mechanical retardation #pectra for the same polymer is often helpful in elucidating the effects of molecular structure and/or microstructure on the observed macroscopic behavior. However, variations in the exact composition, impurities, different thermal and stress histories, or changing microstructural states of separate polymer samples used for electrical and mechanical testing can alter properties, mask correlations, or yield erratic, spurious correlations. Simultaneous measurements of mechanical and electrical properties on the same sample are necessary for meaningful comparisons; this is true for all polymers, but is especially important for biopolymers where time can have a profound effect on mechanical properties, for example. (FITZGERALD, 1975, 1977). Polymers in which temperature or stress induced phase or crystalline transitions take place also have time-sensitive properties as the transitions can occur over long times and produce marked changes in both electrical and mechanical properties (FITZGERALD, 1961). A method and means for sim~kltaneous measurements of the complex shear compliance (J* = J' iJ") and the complex dielectric constant (e* = e' ie") on the same samples of viscous liquids, gels, and solids is reported here. Some data are adduced from simultaneous dielectric and dynamic mechanical measurements on a 10% polyvinyl chloride/di-2ethyl-hexyl phtha!ate gel at audiofrequencies and temperatures from50 to 100~