Mechanistic Study on Reversible Change of Light Scattering Properties of the Polymer Films Involving Dispersed Microspheres of Fatty Acids

Abstract

A mechanistic study has been performed to clarify the reversible change of light scattering properties of the polymer films involving dispersed crystals of fatty acids as microspheres, using X-ray diffractometry, electron microscopy, DSC and supersonic micrography. Special emphasis was laid on two phenomena. (a) The crystallization temperatures (T_c) of the fatty acids remarkably changed, sensitively depending on the degree of melting of the fatty acids at the starting temperature for cooling. The cool ing from far above the melting points lowered T_c about 30° C from the melting point of the bulk crystals. By contrast, T_c was rised when the cooling started from the temperature range of melting. These properties were evidenced by in situ X-ray diffraction measurements of the crystallization processes. (b) The relationship between T_c and the glass transition temperature (T_g) of the polymer matrix definitely influenced the light scattering properties. It was confirmed also that the light scattering state was achieved when T_c was lower than T_g. We have drawn a conclusion that the light scattering property is ascribed to the formation of voids in the micrcspheres, which are formed by the reduction in the volume of fatty acids during the crystallization at the temperatures below T_g of the polymer matrix. The films loses the light scattering property by annihilation of the voids when the crystal surfaces of fatty acids melt upon heating. The nonscattering conditions are maintained even upon the cooling in case that the crystallization occurrs above T_g. The formation and the annihilation of the voids was confirmed as the change of film thickness, and by supersonic micrography.