Pressure effect on the solid–liquid equilibrium forms of odd normal alkanes

Abstract

This paper describes the changes in equilibrium forms of small odd-numbered normal alkane crystals (carbon number: 9, 11 and 13) as functions of temperature, pressure and the carbon number. The crystals were grown by increasing pressure of the liquids using a diamond anvil cell (DAC). After single crystals were prepared in the DAC under high pressure, the crystals were maintained for a long period under constant pressure and temperature. During the changes in the shape of the single crystal, both orthorhombic (high-pressure phase) and hexagonal (low-pressure phase) shapes appeared. These crystal shape variations, depending on pressure and temperature, were consistent for the anisotropies of the orthorhombic and hexagonal unit cells predicted from the molecular arrangements in the unit cells. Hexagonal thin films of n-tridecane could thus grow from the edges of the c-planes of orthorhombic thick plate of parallelogram.