Solvent effect on pressure-induced phase transition in oleic acid

Abstract

With diamond anvil cell as a high pressure apparatus, the high pressure Raman spectra of the 25% (V/V) oleic acid solution with CCl4 as solvent were measured up to 0.84 GPa. Its phase transition process was investigated by analyzing the changes of the Raman bands at different pressures. The results show that oleic acid in 25% (V/V) solution transforms from liquid phase to the crystalline α phase in the 0.15–0.20 GPa pressure range. The degree of the molecular conformational order increases in this transition. In the 0.28–0.40 GPa pressure range, oleic acid in solution further transforms to the crystalline γ phase. This transition is a disorder–order type. In contrast to pure oleic acid, the solidifying pressure of oleic acid in solution is much lower and there is one more intermediate phase (the crystalline α phase) during compression.