聚多硅氧烷为硅源的无裂痕块状气凝胶制备

摘要

The aerogels were prone to cracks due to the shrinkage of wet gel aging and drying.The freecracking gels prepared by polyethoxydisiloxane (PEDS) as silicon source were obtained by the control of water content during the preparation of crosslink gel and aging.Result showed that internal stress generated during the shrinkage of wet gel aging and drying was released due to the low bulk modulus of the wet gels prepared on low water content.When the molar ratio of H20/≡Si- of PEDS was equal to 0.5 by keeping the volume ratio of ethanol/PEDS of 80∶ 20, the free-cracking aerogels were obtained.The morphology of aerogel characterized by high resolution transmission electron microscope(HRTEM) and field emission scanning electron microscope(FESEM) showed that the solid skeleton of pores was composed of a filament of linked nano-particles of 5 ～ 8 nm diameter.Besides, a little of ethanol adsorbed by aerogel during supercritical ethanol drying, the aerogel from theromo-gravimetric and differential scanning calorimetry(DSC-TG) showed the existence of some groups of Si-OC2H5 and Si-OH.At the room temperature, the thermal conduction of the aerogels had a range of 0.028 1 -0.038 1 W/( m· K).%SiO2气凝胶在凝胶老化和干燥过程中极易产生凝胶的开裂.以多聚硅氧烷(PEDS)为硅源,通过在交联凝胶的制备及凝胶老化过程中,控制水的用量,制备出具有无裂痕的SiO2凝胶.结果表明:低水用量获得湿凝胶的抗压模量明显低于高水用量所制备湿凝胶的抗压模量,因此孔结构具有一定的柔性,从而有利于释放凝胶收缩产生的内应力.当H2O与PEDS中Si原子的摩尔比值为0.5时,所得凝胶在H2O体积分数为20%的乙醇老化液中老化后,可以获得完整的无裂痕气凝胶.高分辨透射电镜(HRTEM)和场发射扫描电子显微镜(FESEM)观察表明:所制备的气凝胶是由5～8 nm颗粒串联形成的线状结构体构成.经差示扫描量热-质量损失仪(DSC-TG)分析表明:乙醇超临界干燥所制备的气凝胶,除了表面吸附少量的乙醇分子,还含有Si-OC2H5基团和Si-OH基团.所制备的气凝胶,室温下的导热系数在0.028 1～0.038 1 W/(m·K).