In Situ Interface Design in Graphene-Embedded Polymeric Silica Aerogel with Organic/Inorganic Hybridization

For many practical applications, the most important factor is to have an improved interface between the matrix and dispersed phase in a compressible composite aerogel having a high degree of porosity and a large surface area. Although some measure of compressibility is obtained in polymer-based aerogels with a continuous backbone through the hybridization of the stiff backbone [polyvinyltrimethoxysilane (P-VTMS), -C-C-] and flexible backbone [poly(3-glycidyloxypropyl)trimethoxysilane (P-GPTMS), -C-O-C-], it seems that the extent of improvement is insignificant in terms of interface improvement, surface area increase, and ordered mesoporous network. In this study, the effects of the incorporation of graphene nanoplatelets (GnPs) on aerogels made of a backbone consisting of -C-O-C- (flexible backbone) were examined in terms of structural improvement and were compared with aerogels made of a backbone consisting of -C-C- (stiff backbone). Moreover, the inorganic siloxane cross-link density between the underlying polymer chains was controlled by inducing hydrogen bonding between polymer chains and GnPs. This approach reduces the structural shrinkage during gelation and drying. The integration of only 1 wt % GnP integrated into the backbone by using spinodal decomposition phase separation processing allowed control of the pore size and the surface area. Integration of GnPs through in situ exfoliation during sol-gel transition is shown to be the best approach using the lowest possible amount of GnPs to improve aerogels' mesoporous network made from polymerized GPTMS. A flexible backbone such as P-GPTMS chains is supposed to result in a compliant aerogel, but the chains tend to shrink extensively during gelation and drying, reducing the porosity. P-GPTMS-derived aerogel suffers from a wrong combination of flexible backbone conjugated with an extensive number of permanent chemical cross-links and abundant remaining unreacted hydroxyl groups that undergo permanent chemical shrinkage. To counteract this, the GnP-reinforced prepolymer precursor (P-GPTMS) with fewer siloxane cross-links was synthesized and studied. By use of this strategy, the same elastic properties as those seen with the hybrid P-VTMS- and hybrid P-GPTMS-derived aerogels were imparted, while also improving the mechanical strength by up to 138% and the surface area by up to 205% by controlling the extent of GnP exfoliation during the sol-gel transition. This exceptional effect of GnP on the surface area improvement was shown to be of up to 2.05-fold for P-GPTMS and 2.63-fold for P-VTMS material.