Low-Temperature Phase Transition of Dodecanoic Acid Crystals: A Study Using Raman, Powder X-ray Diffraction, and Density Functional Theory Calculations

Dodecanoid acid, also known as lauric acid, is a molecular alloy phase change material, and as such, knowledge about its behavior under different temperatures is of utmost importance in order to design alloys capable of proper thermal protection. In this manuscript, we identified a phase transition of dodecanoic acid under cooling by Raman spectroscopy coupled with density functional theory calculations and pairs in molecular materials corrections. A complete assignment of the Raman- and infrared-active normal modes of dodecanoic acid crystal in the C form at ambient and low-temperature conditions is also reported in this manuscript. In addition, powder X-ray diffraction of the crystal under low-temperature conditions was carried out in the temperature range of 300-83 K. During cooling, several changes in the crystalline planes and the inter- and intramolecular vibrational bands were interpreted as a reversible structural phase transition. The molecules within the monoclinic structure undergo a polymorphic change from the C form to one of the A phases-presumed herein to be the A(2) form.