Interfacial liquid crystalline mesophase domain on carbon nanofillers in aromatic thermosetting copolyester matrix

This work presents the formation process and thermophysical characteristics of preferentially oriented interfacial liquid crystalline (LC) mesophase domain emerging around graphene nanoplatelet (GNP) particles within an amorphous aromatic thermosetting copolyester (ATSP) matrix. Acetoxy- and carboxylic acid-capped matched oligomers of ATSP interact with oxygen-bearing functional groups on the GNPs during the thermal polymerization process which tethers the nanofillers to the crosslinked polymer backbone. Upon curing, a nematic phase LC network develops at the nanoparticle and matrix interface via the crystalline carbonaceous structure induced local ordering effects. The LC region exhibits a thermally reversible phase transition characteristic; attains an isotropic morphology through a heating cycle and reverses to the nematic form following a subsequent cooling cycle. Solid-state nuclear magnetic resonance spectroscopy analysis reveals the presence of a robust interfacial attachment between the GNPs and ATSP backbone. The strong covalent conjugation induces a marked upshift in the glass transition temperature (T_g) in the ATSP-GNP nanocomposites. Introduction of an LC interlayer region surrounding the nanofillers facilitated by a strong interfacial attachment mechanism could help to optimize the performance of polymer nanocomposites.