Simple Landau Model of the Liquid-RII-RI Rotator Phases of Alkanes

Abstract

Simple Landau free energy function is presented to describe the Liquid-R II -R I phase sequence of alkanes and transitions between them. The order parameters necessary to describe these rotator phase transitions are identified. We present a mean-field description of the Liquid-R II and Liquid-R I transitions. General arguments are presented for the topology of the phase diagram in the vicinity of the Liquid-R II -R I triple point. Within this model the Liquid-R II and Liquid-R I transitions are found to be always strongly first order. Calculations based on this model agree qualitatively with experiments.

Pressure Effect on Thermodynamic Quantities for the Solid-Liquid Phase Transition in n-tridecane, n-hexadecane and n-octadecane

“…where the coefficients are assumed to depend on the temperature, pressure and concentration, in general. For the solidliquid equilibria, we have the first order condition that [38] 𝐹 𝑠 = 𝐹 𝐿 = 0 (2) by considering the fact that in the liquid phase there is no ordering (𝐹 𝐿 = 0). For the SLE, the coefficients are 𝑎 2 > 0, 𝑎 4 < 0 and 𝑎 6 > 0 for the first order transition as defined by the Landau mean field theory.…”

Phase Change Materials for Textile Application

“…These high-temperature phases maintain an organized structure. In these rotator phases noted, respectively, β-RI and α-RII, the disorder is caused by a 180° rotation of some chains around their axis, which allows them to take a balanced position [24].…”