Crystallization-driven migration of the low surface energy segment of a copolymer to the bulk

[(BA-C8)18-(6FBA)]n was synthesized by condensation polymerization of poly(bisphenol A-co-octane) containing 18 repeat units with bromine end groups, (Br-(BA-C8)18-Br), and 4,4′-(hexafluoroisopropylidene)diphenol (6FBA). This copolymer was confirmed to be semicrystalline after a single melting temperature was detected by differential scanning calorimetry. The changes in the surface chemical composition were measured using time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy, the changes in the surface energy were measured using contact angle measurements, and the changes in the surface morphology were detected using atomic force microscopy as the copolymer crystallized. A decrease in the surface fluorine concentration with time was detected because of the movement of the low surface energy units (6FBA) to the bulk during the development of the crystalline phase. This result shows that the decrease in the enthalpy as a result of crystallization overcomes the increase in the surface free energy due to the migration of the low surface energy units to the bulk and the decrease in entropy due to demixing.