Gel-Phase Processing and Solvent Exchange

Several important unit operations involved in aerogel production pertain to the formation and processing of gels. Formation of a gel typically occurs in a mold, and accordingly, important considerations should be given to gel molding. Furthermore, after a gel has been formed, additional processing steps are typically required before its pore fluid can be removed to produce an aerogel. Such steps include aging of the gel to strengthen its solid-phase backbone, diffusion-mediated replacement of its pore fluid with a target solvent to compatibilize the gel for drying, and optional liquid-phase chemical treatment(s), for example, to impart hydrophobicity, introduce a desired functionality, or increase strength. This chapter discusses important unit operations including molding and demolding, aging, and solvent exchange, as well as examples of liquid-phase chemical treatments used to prepare various functional aerogels.