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

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 degrees C), a long-range ordered body-centered cubic (BCC) lattice was formed at ca. 130 degrees 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 degrees C. Interestingly, if the crystallized gel was heated to a relatively low temperature (120 degrees C) and cooled down, although the microstructure was still disordered after the paraffin crystallization, the longrange 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 degrees 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 degrees C, and its crystallization deformed the PS microdomains, resulting in the absence of an ordered microstructure even with the remelting of paraffin.

Automated summary

The microstructure evolution of SEBS/crystallizable paraffin gel during cooling and reheating was studied. It was found that an ordered BCC lattice formed at a higher temperature and disappeared with the crystallization of paraffin. During reheating, a new BCC lattice was formed. When the gel was heated to a lower temperature and cooled, the ordered BCC lattice immediately reappeared during paraffin remelting.