Study On Preparation Of Nanosheets By Supercritical Fluids And Its Thermal Properties

Graphene and tiania nanosheets possess many outstanding properties. However, how to achieve mass production is still a challenge. To explore a new way of preparing nanosheets material has very important practical significance. Supercritical fluid shows unique characteristic, such as outstanding wetting of surfaces, low interfacial tension, low viscosity, and high diffusion coefficients. These features facilitate supercritical fluid to accomplish penetration and exfoliation of layered materials. This article focus on the key technical problems in the preparation process of supercritical fluid and heat performance.The yield of graphene is impacted by supercritical parameters, initial material, and repeated treatment. The best operation paraments was obtained. Natural graphite was treated slightly by nitric acid, some polar functional groups(C-OH,-COOH) was attached on the surface of graphite, it enhance the yield of graphene sheets and maintain high quality.A way for reducing graphene oxide by supercritical(subcritical) water is proposed. Moreover, the function of H~+ catalyzed dehydration for GO reduction under supercritical(subcritical) water is confirmed by comparison experiments. GO is treated by hydrothermal(200?-400?). This method is green, fast, simple, efficient. In order to explore the mechanism of GO reduction, dispersing graphite oxide in DMF, treating it at the same temperature. We found that water is a typical protic solvent, it can produce large amounts of H~+, which enhances the reducing power of water.A way for preparing titania nanosheets by supercritical DMF exfoliation of layered H1.07Ti1.73O4·H2O is proposed and how to select solvent as supercritical fluids is the key problem. In order to explore this rule, we have designed some experiments, these results showed that exfoliation is found in supercritical DMF, while in supercritical water exfoliation and the phase transition occur concurrently, as water is a protic solvent, it can supply H~+ under high temperature and high pressure conditions, and explored the mechanism of phase transition. XRD and SEM results confirmed that the cause of the phase transition from layered titanate to anatase is dissolution and recrystallization.With rapid development of electronic industry towards high integration and high power direction, the demand for efficient thermal interface materials becomes important. Graphene possess high thermal conductivity and low Kapitza resistance, is the best ideal nano filler for graphene-epoxy composites. We have used the graphene form the method of supercritical exfoliation and reduction as a filler for graphene-epoxy composites, the graphene loadings varying between 2- 10 vol %. As a result, the thermal conductivity of the composites significantly increases compared to the pristine epoxy. Moreover, calculating the thermal conductivity of composites by theoretical prediction model, it was consistent with the result of experiments.