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

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 pi-pi 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.