Enhanced interfacial rigidity of 1D thermoset nanostructures by interface-induced liquid crystallinity

Abstract

Polycyanurate networks (PCNs), which form random networks in the bulk, are representative of an important class of thermosetting materials. We show that free surfaces of PCNs exhibit rigidity enhanced by one order of magnitude (quantified by Young's modulus) if they are initially synthesized in the presence of hard confining interfaces, such as the pore walls of nanoporous anodic aluminum oxide (AAO). Using self-ordered AAO, which contains arrays of aligned cylindrical nanopores uniform in length and diameter as an inorganic model matrix, we could evidence interface-induced liquid-crystalline ordering of the liquid cyanate ester monomers (CEMs) at the pore walls. The interfacial ordering of the CEMs, which is conserved upon curing, is most likely the origin of enhanced rigidity of the free PCN surfaces after release of the one-dimensional PCN nanostructures from AAO. The results presented here should be of considerable relevance for the processing of industrially relevant thermosets, for the understanding of polymer/solid interfaces, for the design of advanced nanocomposites for applications in aviation and high-speed electronics, and for the design of mechanical hybrid nanostructures for advanced biomimetic adhesive systems.