Microstructure evolution during cooling and reheating of the physical gel composed of SEBS copolymer and crystallizable paraffin

Abstract

The microstructure evolution of poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS)/crystallizable paraffin gel during cooling and reheating was investigated using small angle X-ray scattering (SAXS). By analyzing the change of SAXS profiles, it was found when cooling from a relatively high temperature (180 °C), a long-range ordered body-centered cubic (BCC) lattice was formed at ca. 130 °C and remained stable before the paraffin was crystallized. With the crystallization of paraffin, the ordered lattice disappeared and the polystyrene (PS) microdomains were deformed. During reheating, when the paraffin was remelted, the destroyed ordered lattice did not reappear immediately, and a new BCC lattice was formed when the temperature was further increased to approximately 100 °C. Interestingly, if the crystallized gel was heated to a relatively low temperature (120 °C) and cooled down, although the microstructure was still disordered after the paraffin crystallization, the long-range ordered BCC lattice immediately reappeared as the paraffin was remelted, and the PS microdomains were not obviously deformed during paraffin crystallization and remelting. Based on the different microstructure evolution behaviors when cooling from 180 and 120 °C, and the fact that midblock selective solvent would be trapped into the PS microdomains during gel formation, we speculated that a part of the paraffin was imbibed into the PS microdomains when cooling from 180 °C, and its crystallization deformed the PS microdomains, resulting in the absence of an ordered microstructure even with the remelting of paraffin.