Production of Porous Materials by Supercritical Carbon Dioxide Drying

采用超临界CO2对硅胶醇凝胶进行干燥，考察了不同粒径硅胶醇凝胶的最佳干燥条件。实验发现，在某些凝胶中，液相中出现了非平衡界面，温度对时间的影响较小。样品厚度的增加严重影响了干燥过程的各个阶段，导致干燥时间延长。凝胶上的硅烷醇基团的疏水改性也在超临界干燥过程中使用三个甲基甲氧基硅烷进行。疏水改性的效果进行了评估，通过测量水吸附。在超临界流体相中用甲基三甲氧基硅烷改性的气凝胶样品显示出比在超临界干燥过程之前在液相中改性的那些更高的疏水性。

Drying of silica alcogels using supercritical carbon dioxide was carried out at various conditions to investigate the optimal drying conditions for samples with different sizes. From the experiments it was found that a non-equilibrium interface that appeared in fluid phase in some gels, while the tem perature had a minor influence on the time. An increase in the sample thickness affected all stages of the drying process seriously, resulting in longer drying times. Hydrophobic modification of silanol groups on the gels was also performed in the middle of the supercritical drying process using three methylmethoxysilanes. The effects of the hydrophobic modification were evaluated by measuring water adsorption. The aerogel samples modified with methyltrimethoxysilane in the supercritical fluid phase showed higher hydrophobictiy than those modified in the liquid phase prior to the supercritical drying process.