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(vinyl idene fluoride)/poly(methyl methacrylate) (PVDF/PMMA) blends was carried ou t. Dielectric relaxation spectroscopy (DRS) was performed over 11 decades o f frequency and over a wide range of temperature on wholly amorphous, cryst alline, and crystallizing blends of varying composition. The range of exper imental 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 detec ted, 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 amorpho us PVDF segments (not only within the crystalline-amorphous interphase); th e alpha(m) process, which encompasses several relaxation processes and scal es with blend composition; and the alpha(c) process, attributed to relaxati ons 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 molec ular and polymeric glass formers. An explanation of the underlying physics was offered within the framework of an interplay between the physical dimen sion of various nanoscopic regions in the blend and the characteristic leng th scale for cooperative relaxation. The alpha(a)beta(a) crossover was show n to be a consequence of the confinement imposed on the amorphous PVDF segm ents by more rigid PMMA segments and the PVDF crystals.