Fourier transform infrared spectroscopic study of the kinetics of a first-order phase transition in tridecanoic acid CH3(CH2)11COOH

Abstract

The structural changes in crystalline lamella cores of tridecanoic acid CH₃(CH₂)₁₁COOH during heating in the range from the temperature T₁ = 13.5°C to T₂ > T_m = 41.6°C have been investigated using Fourier transform infrared spectroscopy. The behavior of the bands of rocking (in the region of 720 cm^–1) and bending (in the region of 1470 cm^–1) vibrations of CH₂ groups in tridecanoic acid methylene segments has been analyzed. It has been shown that, in the first-order phase transition region (T_s–s ~ 36°C) within a narrow temperature range (ΔT₁ ≤ 1 K), there is a gradual transformation of the initial triclinic subcell into the hexagonal subcell. The mechanism of this transition has been considered in terms of the theory of diffuse first-order phase transitions.