Surface chemical composition and conformation of liquid crystalline polymers studied with ToF-SIMS and XPS

In this work, we examined the effects of the liquid crystalline ordering on the surfaces of thermotropic fluorocarbon-hydrocarbon polymers (FmHn, with m = 8; n = 8, 10) by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) combined with principal component analysis (PCA). XPS results showed that the liquid crystal surfaces of the polymers were enriched with hydrocarbon segments. PCA of ToF-SIMS data further showed that reversible structural changes between the amorphous and ordered states of the polymers occurred. As these polymers ordered at room temperature, their surfaces were transformed from the amorphous state with fluorocarbon-segment enrichment to the fully ordered liquid crystal states with hydrocarbon-segment enrichment. All these results suggested that the molecular orientation controlled the surface composition of the liquid crystalline polymers notwithstanding the surface energy. The axial alignment of the rigid fluorocarbon mesogens anchored the flexible hydrocarbon segments at the surface. Copyright © 2010 John Wiley & Sons, Ltd.