Thermal diffusivity and heat capacity of poly(vinylidene fluoride)/poly(methyl methacrylate) blends by flash radiometry

Abstract

The thermal diffusivity D and the relative heat capacity HC were measured for poly(vinylidene fluoride)/poly(methyl methacrylate) (PVDF/PMMA) blends by flash radiometry. The effect of the crystal form on D of these polymer blends as well as the dependence of D and HC on temperature were discussed. In the PVDF content region between 70 and 80 wt%, the blend samples preferentially form the β crystal phase when they are prepared by melt quenching. The dependence of D on PVDF content for the melt-quenched sample showed a noticeable change in the composition region in which the β crystal phase is formed. D decreased with increasing PVDF content up to 70 wt% and then increased up to 100 wt%, showing a peak between 75 and 80 wt%. From the X-ray diffraction patterns, the crystallinity of the blends monotonically decreases with decrease of PVDF content. The results imply that the peak in D in the melt-quenched 75 25 and 80 20 PVDF/PMMA blends is not related to the crystallinity but to another structural factor. The temperature profile of D showed inflection points corresponding to the glass transition temperature and the melting temperature of the α crystal phase. The temperature profile of HC exhibited changes of HC due to the melting transition of the β and α crystal phases. These points from the temperature profile of D and HC correspond well to those from thermal analysis.