Deviation of phase transition process in surface-tethered thermotropic liquid crystalline polymer nanocomposites with graphene oxide: a spectroscopic study

Abstract

Temperature-resolved FTIR spectroscopy in combination with two-dimensional correlation spectroscopy (2Dcos) was employed to elucidate the dynamic mesophase transition behavior of poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PMPCS) blended with PMPCS grafted graphene oxide (GO-PMPCS) nanofiller. After integration with 2.0 wt% nanofiller, the columnar nematic phase of polymer nanocomposites was retained while deviation of the mesophase transition temperature was identified, which was ascribed to the π–π stacking interactions and charge transfer effect between polymer and GO sheets revealed by Raman and X-ray photoelectron spectroscopy. Based on 2Dcos analysis, a sequential group motion from aromatic rings to carbonyl groups and main chains was discerned at the early stage of the phase transition. It was concluded that surface-tethering of the PMPCS matrix onto GO sheets may be preferred before the mesophase development. A two-step mesophase transition process defined as a physical adsorption process and a mesophase development process under physical cross-linking was illustrated.