Reorientational dynamics of poly(vinylidene fluoride)/poly(methyl methacrylate) blends by broad-band dielectric relaxation spectroscopy

A comprehensive investigation of the reorientational dynamics of poly(vinylidene fluoride)/poly(methyl methacrylate) (PVDF/PMMA) blends was carried out. Dielectric relaxation spectroscopy (DRS) was performed over 11 decades of frequency and over a wide range of temperature on wholly amorphous, crystalline, and crystallizing blends of varying composition. The range of experimental conditions and compositional variables far exceeded those employed by previous investigators, enabling us to formulate a comprehensive view of the dynamics in these systems. A number of relaxation processes were detected, and their origins, temperature dependence, composition dependence, and spectral characteristics were established. Three alpha-type processes were observed: the alpha(a) process, associated with relaxations of all amorphous PVDF segments (not only within the crystalline-amorphous interphase); the alpha(m) process, which encompasses several relaxation processes and scales with blend composition; and the alpha(c) process, attributed to relaxations within the crystalline phase. With decreasing temperature the alpha(a) process in the blends undergoes a crossover to a localized beta(a) process, in a manner different from the alpha beta splitting observed in many molecular and polymeric glass formers. An explanation of the underlying physics was offered within the framework of an interplay between the physical dimension of various nanoscopic regions in the blend and the characteristic length scale for cooperative relaxation. The alpha(a)beta(a) crossover was shown to be a consequence of the confinement imposed on the amorphous PVDF segments by more rigid PMMA segments and the PVDF crystals.