Determination of phase transition temperatures (melting, crystallization, rotator phases) of n-alkanes by the optical method

Abstract

The temperatures of phase transitions (melting, crystallization, rotator phases) were determined for a number of individual n-alkanes from C19H40 (n-nonadecane) to C28H58 (n-octacosane) by the optical method, a modified droplet technique. For this research, n-alkanes were presented as an emulsion in water without the addition of surfactants. Emulsions were prepared by ultrasonic dispersion of a small amount of n-alkane in water at a temperature above the melting point of the investigated n-alkane. The hydrodynamic radius of the dispersions measured by the dynamic light scattering (DLS) method was about 100 nm and did not change within a wide temperature range within the measurement accuracy. The temperatures of melting, crystallization, and rotator phase transitions of pure n-alkanes in the form of emulsion were determined from temperature-dependent measurements of the light scattering by the dispersions. The supercooling values for studied n-alkanes were also determined.