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Resorcinol formaldehyde (RF) aerogels with graded density were fabricated via three methods: layer-by-layer gelation, sol-co-gelation and continuous formation technics.The growth of gel particles was studied, which was closely correlated with the concertation of reactants and catalyst.Meanwhile the diffusion effect of sol and gel was studied, which influenced the formation of graded density structures and the appearance of interface between different aerogel layers.The sol was derived from resorcinol, formaldehyde and water, which was catalyzed by sodium carbonate, and the density gradient along the through-thickness direction was controlled by regulating the gelation process of the different precursors and the sequence of superposition of sol layers.Qualified RF aerogels with stepped density, quasi-continuous density, and continuous density were obtained after a serious of steps mainly including gelation formation, demolding, solvent exchange and supercritical drying.The morphology of the samples were characterized by scanning electron microscope (SEM) and the densities were characterized by both the backups and the X-ray phase contrast imaging instrument.The thickness of the samples were ~1 cm and the density of them were ~200-600 mg/cm3, varying from one side to the other side.The appearance of samples fabricated by different methods looked widely different and the significance level of interfaces between layers were different as well.In particular, there was obvious interface insulating aerogel layers in the samples obtained from layer-by-layer gelation method, which made the density profile break around the interface.The interface of the samples obtained from sol-co-gelation method looked more indistinct and the density profile looked quasi-continuous.The interface of the samples obtained from continuous formation technics was almost invisible and the density profile looked smooth.