Rapid fabrication of cross-linked silica aerogel by laser induced gelation

• Polymer cross-linked silica alcogels are produced in a matter of seconds by illuminating the gelation solution with a laser beam (λ = 532 nm), causing photopolymerization and gelation.
• Solution used includes TEOS, AlCl3·6H2O, Eosin Y, hexanedioldiacrylate, trimethoxysilylpropyl methacrylate, and an amine.
• The role of pre-heating, irradiation conditions, amine and gelation solvent on gelation behavior, structural and mechanical properties of the ensuing aerogels were explored.

A method for rapid fabrication of polymer cross-linked silica aerogel through laser induced photogelation and the effect of pre-heating, irradiation conditions, and gelation solvent on the structural and mechanical properties of the resulting aerogel material is presented here. An ethanolic solution of an alkoxysilane (tetraorthosilicate, TEOS), a monomer (hexanedioldiacrylate, HDDA), a visible-light free-radical photoinitiator (Eosin Y) and a tertiary amine (as co-initiator and pH modifier), was prepared. The solution was irradiated with a laser beam, and the energy liberated by the polymerization reactions induced gelation in a matter of seconds. The alcogel was then dried into aerogel using the ethanol-water (or acetone-water) azeotrope mixture as a drying fluid. It was observed that pre-heated solutions gelled instantly and the resulting aerogels showed density, Young's modulus and surface area values comparable to those of aerogels produced through conventional methods. The solutions without pre-heating gelled relatively slowly and yielded composites with Young's modulus values about 3 times and surface areas about 1.5 times smaller than the pre-heated samples. The replacement of ethanol with acetone as a gelation solvent accelerated gelation; however, the composites shrank about 2 times more than samples prepared using ethanol and, consequently, had higher densities and moduli and decreased surface areas. The potential exists for mold-free and rapid fabrication of bulk or thin film aerogel structures using this method to open new avenues for their application in areas such as 3D printing.

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