The role of N,N-dimethylformamide, a DCCA, in the formation of silica gel monoliths by sol-gel method

Abstract

In order to find the role of N,N-dimethylformamide (DMF), a newly found DCCA (drying control chemical additive), in producing silica gel monoliths by the sol-gel method, microstructures of the silica gel monolith prepared from tetramethoxysilane (TMOS) solutions containing DMF and formamide, respectively, have been examined. Dry gels prepared from the solutions containing DMF and formamide had larger pores, which was interpreted to be one of the effects of the DCCA in suppressing occurrence of cracks and fractures in the process of drying wet gels. When drying gel discs prepared from solutions containing DMF were exposed to the vapors and, subsequently liquids of DMF, formamide, methanol and water whose surface tensions are different from each other, cracks were generated for formamide and water having high-surface tensions and no cracks were produced for DMF and methanol. This was interpreted to indicate that the low surface tension of DMF may be one of the effects in protecting the drying gel from crack generation. It was assumed that DMF vaporizes at last during the drying process and weakens the capillary force exerting on the silica network structure.