Wang Shengnan, Wang David K, Smart Simon, Diniz da Costa João C
The University of Queensland, FIM2Lab - Functional Interfacial Materials and Membranes Laboratory, School of Chemical Engineering, Brisbane Qld 4072, Australia.
Sci Rep. 2015 Sep 28;5:14560. doi: 10.1038/srep14560.
A ternary phase-separation investigation of the ethyl silicate 40 (ES40) sol-gel process was conducted using ethanol and water as the solvent and hydrolysing agent, respectively. This oligomeric silica precursor underwent various degrees of phase separation behaviour in solution during the sol-gel reactions as a function of temperature and H2O/Si ratios. The solution composition within the immiscible region of the ES40 phase-separated system shows that the hydrolysis and condensation reactions decreased with decreasing reaction temperature. A mesoporous structure was obtained at low temperature due to weak drying forces from slow solvent evaporation on one hand and formation of unreacted ES40 cages in the other, which reduced network shrinkage and produced larger pores. This was attributed to the concentration of the reactive sites around the phase-separated interface, which enhanced the condensation and crosslinking. Contrary to dense silica structures obtained from sol-gel reactions in the miscible region, higher microporosity was produced via a phase-separated sol-gel system by using high H2O/Si ratios. This tailoring process facilitated further condensation reactions and crosslinking of silica chains, which coupled with stiffening of the network, made it more resistant to compression and densification.
以乙醇和水分别作为溶剂和水解剂，对硅酸乙酯40（ES40）溶胶 - 凝胶过程进行了三元相分离研究。在溶胶 - 凝胶反应过程中，这种低聚物二氧化硅前体在溶液中会随着温度和H₂O/Si比的变化呈现出不同程度的相分离行为。ES40相分离体系不互溶区域内的溶液组成表明，水解和缩合反应会随着反应温度的降低而减少。一方面，由于溶剂缓慢蒸发产生的较弱干燥力，另一方面，未反应的ES40笼状结构的形成，在低温下获得了介孔结构，这减少了网络收缩并产生了更大的孔隙。这归因于相分离界面周围反应位点的浓度，其增强了缩合和交联。与在互溶区域中通过溶胶 - 凝胶反应获得的致密二氧化硅结构相反，通过使用高H₂O/Si比的相分离溶胶 - 凝胶体系产生了更高的微孔率。这种定制过程促进了二氧化硅链的进一步缩合反应和交联，再加上网络的硬化，使其更耐压缩和致密化。
