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酚醛树脂和羟甲基化蜜胺在碱性水溶液中在 85℃水浴中反应 5d经溶胶 -凝胶过程形成了水凝胶。水凝胶经丙酮置换产生酮凝胶 ,而后经超临界二氧化碳干燥生成有机气凝胶。有机气凝胶在氮气氛中 80 0℃下裂解3h形成了炭气凝胶。采用小角X -射线散射技术和散射理论对上述四种凝胶的微结构进行了分析。结果发现 :水凝胶粒子是单分散的 ,被水溶胀并在 0 .15nm处有强的散射峰 ,表明具有纳米尺度的空间周期结构 ,这种结构是通过不稳态纳米尺度相变———旋节微相分离产生的。由丙酮置换产生的酮凝胶也是单分散的 ,被丙酮稍微溶胀并在0 .15nm具有肩峰 ,表明水凝胶在溶剂置换过程中发生轻微团聚产生的大粒子在较小角处发生强烈的散射致使强峰演化成肩峰。有机气凝胶和炭气凝胶都是多分散的 ,在小角处没有散射峰 ,表明在超临界干燥过程中粒子的团聚继续发生导致多分散性并掩盖了纳米尺度的空间周期结构致使散射峰消失。有机气凝胶中存在的扩散界面层在其裂解过程中消失 ,这可能是由于在裂解过程中扩散界面层向粒子迁移以降低界面能所致。从小角X -射线散射数据用Shull Roess法得到的有机气凝胶和炭气凝胶的回转半径分布比较可知 ,在裂解过程中 ,粒子的团聚长大、质量损失和致密化共同作用的结果使得炭气凝胶的回转半
The phenolic resin and methylolated melamine reacted in aqueous alkaline solution at 85 ℃ for 5 days to form hydrogel by sol-gel process. The hydrogels are displaced by acetone to produce ketone gel, and then dried by supercritical carbon dioxide to generate organic airgel. The organic aerogels were pyrolyzed for 3h at 80 ℃ in a nitrogen atmosphere to form carbon aerogels. The microstructures of the above four kinds of gels were analyzed by using small angle X - ray scattering and scattering theory. The results show that the hydrogel particles are monodisperse, water-swollen and have a strong scattering peak at 0.155 nm, suggesting a nanoscaled, space-cycle structure that is formed by the unsteady nanoscale phase transition- - Spinning micro-phase separation generated. Ketones gels produced by acetone displacement are also monodisperse, slightly swollen with acetone and have a shoulder at 0.155 nm, indicating that the large particles that result from slight agglomeration of the hydrogel during solvent displacement occur strongly at smaller angles Scattering causes strong peaks to evolve into acromion. Both the organic airgel and the carbon airgel are polydisperse with no scattering peaks at small angles indicating that particle agglomeration continues to occur during supercritical drying resulting in polydispersity and obscuring the nanostructured spatial period structure leading to scattering peaks disappear. The diffusive interfacial layer existing in the organic airgel disappears during the pyrolysis, which may be due to the migration of the diffusive interfacial layer to the particle to reduce the interfacial energy during the pyrolysis. From the small angle X - ray scattering data obtained by Shull Roess method obtained organic airgel and carbon aerogels radius of rotation distribution comparison shows that in the cracking process, the particle agglomeration and growth, mass loss and densification of the combined effect of the results Carbon airgel rotary half