Production of Porous Materials by Supercritical Carbon Dioxide Drying

用超临界二氧化碳对硅醇凝胶进行了不同条件下的干燥实验，研究了不同尺寸样品的最佳干燥条件。实验发现，在某些凝胶中，流体相中出现了非平衡界面，而温度对时间影响不大。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。在超临界干燥过程中，还使用三种甲氧基硅烷对凝胶上的硅醇基进行了疏水修饰。通过测定吸水率来评价疏水改性的效果。超临界流体相中甲基三甲氧基硅烷改性气凝胶样品的疏水性高于超临界干燥前的液相改性气凝胶样品。

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.