Properties of high-pressure solvents for fullerenes

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Solubility phenomena of C60 in toluene was observed under high pressure. Before doing it, some improvements for high-pressure equipment have been done to keep the high pressure in the vessel for several months because the equilibration for the solubility takes a long time of several days or weeks. One of the improvements was done by selecting a heat-treated copper as a material for the gasket and by cutting it with an accuracy of 0.01 mm to fit it to the cylinder of the high-pressure cylinder.Two solubility (x in mole-fraction unit) -pressure (p)-temperature (T) surfaces were observed for C60 in toluene suggesting an phase transition in solid phase. These surfaces were drawn in the following equations, respectively.lnx+5.087-8.426x10^3(p/MPa)-15.385x10^<-6>(p/MPa)(high pressure and low temperature)lnx-10.9612+943.881(T/K)+[261(T/K)-0.0724](p/MPa)(low pressure and high temperature)Using hexane. as a solvent in the next step, high-pressure solubility of C60 was also measured. It showed a breaking of the surface suggesting a phase transition at a high pressure as well as C60 in toluene. The solubility increased after the phase transition though that in toluene decreased. Such difference in the high-pressure solubility suggests that the structure of solvated solids which coexist with saturated solutions differs from each other.