Gas Expanded Liquids: Thermodynamic Property Investigation And Application In MWNTs' Functionalization

Solvent usage has been linked to waste generation and associated with environmental and economic burdens. To find a new green solvent is one of the solutions to solve our problem. Gas expanded liquids (GXLs) is a new and green media whose development is based on supercritical fluids in recent years. The research and applications of GXLs have great theoretical and practical value. To understand the versatile properties of GXLs and explore its potential applications is still a critical problem we have to face. Accordingly, the work in my thesis is described in the following two parts:the solvent property investigation of GXLs and its potential applications in MWNT functionalization as shown below:Part one:Tautomerism equilibrium of ethyl acetoacetate (EAA) in gas-expanded liquids (CO2+methanol) was measured by UV-Vis spectroscopy at 298.15K (or 313.15K) with pressures along the bubble point curve of the corresponding CO2+methanol phase diagram. The volume expansion coefficient (a) of the gas-expanded liquids was also determined at different pressures along the bubble point curve of the vapor-liquid equilibrium at 313.15K and 298.15K, respectively The equilibrium constant (Kc) of EAA in the binary mixtures was calculated, and the dependence of Kc as a function of pressure and temperature was also studied. The results are shown as follows:Firstly, it's found that the volume expansion coefficient is rising with the increasing pressure. The change in volume expansion coefficient isn't obvious at low pressures but dramatical at high pressures.Secondly, the pressure dependence of Kc in GXLs:Kc at 298.15K does not change significantly within low pressure range. However, Kc increases rapidly at high pressures when pressure is greater than 4.5 MPa. The similar trend is also observed at 313.15 K.Thirdly, through the pressure dependence of Kc, it is found that the polarity of CO2+methanol mixtures gradually decreases with increasing CO2 mole fraction.Part two:The free radical polymerization of poly-4-vinylpyridine(P4VP) was carried out using 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) radical as a capping agent. A series of different molecular weight (2169,17290 and 29900) of poly 4-vinyl pyridine (P4VP) were prepared. Then P4VP was mixed with multi-walled carbon nanotubes in a new and green system, the gas expanded liquids of CO2-DMF. A series of pressures (7.11MPa,9.56MPa,13.6MPa,14.6MPa and 16.0MPa) were chosen along the vapor-liquid bubble point curves of CO2-DMF at constant temperature 125℃. Finally, carbon nanotubes were successfully modified by P4VP in CO2-DMF. The P4VP modified MWNT can be dispersed not only in organic solvents but also in the aqueous solution of acid. Furthermore, the modified MWNT was characterised by TGA, TEM and Raman Spectra. The results show that it has more advantages in gas expanded liquids than in conventional solvents. We can not only much reduce the amount of organic solvent usage but also control the polymer grafting yield on MWNT by facile pressure tuning of GXLs.