ROLES OF NANOPARTICLE FILLERS DURING NANOSTRUCTURE SELF-ASSEMBLY IN THE ENHANCEMENT OF NANOCOMPOSITES BARRIER PROPERTIES

Abstract

During self-assembly, the nanostructure of materials builds itself ‘spontaneously’ through local non-covalent interactions. This process of organization consistently applies to the higher meso- and macroscopic scales of ordering and thus governing the materials properties. Self-assembly can be rationally designed and is a practical strategy to build a nanostructure. This review discusses the effect of various manners of self-assembly due to various degrees of interactions between nanoparticle fillers and polymer matrix in enhancing nanocomposites properties, especially the barrier properties, and in particular fire retardancy. The assembly of three-dimensional structures of polyurethanes, for instance, is governed by microphase separation due to hydrogen bonding (10-65 kJ mol-1 of strength) within the hard phases of polyurethane foams (~10 nm of size). The microphase separation is influenced by the existence of nanoparticle fillers in the nanocomposites, to the extent that they may become either nucleation sites and catalysts for cell growth and coalescence, physical hindrance to hydrogen bonding and microphase separation, or perhaps somewhere in between. In the case of flexible polyether-urethane/layered-silicate nanocomposite, it was clearly observed that the presence of a molecular scale ingredient brings about an additional rule of assembly to the reacting mixture, resulting in a relatively better organized structure. Therefore, in order to engineer and control fire retardancy and other barrier properties of nanocomposite materials, the nature and mechanism of their self-assembly in the presence of nanoparticle fillers needs to be well understood.