LAUSR

Abstract The present paper examines molecular motion mechanisms in lamellar molecular crystals of undecylenic acid. Thermophysical, dielectric, and infrared spectroscopy methods were used to demonstrate the presence of a relaxation process in crystals of undecylenic acid in the temperature range of −60°С to −10°С. The process is thought to be due to the free rotation of carboxylic groups after dissociation of dimeric rings (which the undecylenic acid forms via hydrogen bonds) and the nucleation of topological solitons. Topological solitons originate once the carboxylic groups begin to rotate freely. This hypothesis does not contradict the calculations of the dielectric permittivity increment performed in accordance with the model of a system of identical relaxators, each of which has two non-equivalent positions separated by a potential barrier. For this model, the change in dipole moment per unit volume due to carboxylic group free rotation and the propagation of topological solitons along carbon chains was calculated. The dielectric permittivity calculations for the model of several solitons nucleating simultaneously matched the experimentally obtained values. The topological soliton hypothesis was also confirmed by comparing the experimentally obtained activation energy value (101 kJ mol−1) with the hydrogen bonds energy (29 kJ mol−1 each) and the nucleation of a topological soliton energy (40 kJ mol−1).