Molecular collapse – modification of the liquid structure induced by pressure in oleic acid

Abstract

Recently we showed that in case of the oleic acid (C ₁₈ H ₃₄ O ₂), the transition to the high-pressure, strong scattering of light phase is quite complicated. This article presents further analysis of structure changes of the investigated liquid during its transformations. The basis of the analysis are measurements of the transmitted and scattered light intensity and temperature changes as a function of time after the application of pressure. During the decompression and the return to the initial state, the intensity of the scattered light increases several times. The automatic pressure system allowed us to observe six pressure regions of the liquid structure modification during the pressure rise. In the fourth region of applied pressure, the molecules spontaneously draw onto themselves, enlarging the available free volume that causes the further volume reduction with compression and does not produce a pressure change. We called the phenomenon a molecular collapse.

Keywords:

• phase transition
• molecular collapse
• high pressure
• light scattering