Strong, highly hydrophobic, transparent, and super-insulative polyorganosiloxane-based aerogel

Wide application of hybrid silica aerogels is limited by the costly preparation process and poor mechanical properties due to the inadequate initial connectivity at the interparticle regions. Most of the conventional solutions come at the cost of increased processing time, density and thermal conductivity. This paper reports a rapid and simply prepared 3-(trimethoxysilyl)propyl methacrylate (TMSPMA)-based aerogel with ultra-low density, high mechanical properties, extremely low thermal conductivity (10 mW·m−1 K−1), and high hydrophobicity. The overall connectivity state was tuned by manipulating the nano-architecture of the aerogel structure. This involved tailoring the constituent materials at the molecular level, the sequence of the reactions, thermodynamics and the processing parameters. Two novel approaches were explored. First, a post-gelation free radical self-curing (SC) method with no added organic moieties was examined. The reaction sequence and the precursor nature were then changed. The free radical polymerization was performed first to obtain a novel macro-precursor (PTMSPMA), followed by hydrolytic polycondensation. Adjustment of the thermodynamic variables during gelation led to two different structures, pearl necklace-like and reticulate. The reticulated PTMSPMA-derived aerogels exhibited the lowest density, lowest total thermal conductivity, and the highest compression modulus. Further modification of reticulated aerogel processing conditions surprisingly showed that the choice of alcohol has profound impact on the mechanical properties, transparency, and surface properties (hydrophobicity) of aerogels by tailoring the molecular assembly. While ethanol created a super hydrophilic aerogel, benzyl alcohol rendered a highly hydrophobic aerogel.