Influence of the Hydroxyl Position in Racemic Hydroxyoctadecanoic Acids on the Crystallization Kinetics and Activation Energies of Gels and Dispersions in Mineral Oil

Abstract

Minor changes in molecular structure affect the ability of racemic hydroxyoctadecanoic acids (nHSA, where n is the position of the hydroxyl group) to form molecular gels in a low polarity liquid, mineral oil, and influence their supramolecular structures. The activation energy and energy released during crystallization of 2HSA and 3HSA from solutions or sols are significantly lower than those of 6HSA, 8HSA, 10HSA, 12HSA, and 14HSA. The lower activation energies are associated with the ease of molecules of 2HSA or 3HSA to add to a face of a growing crystal lattice or the ease in which the critical nuclei are reached; the change in the activation energies appears to be related, in part, to the critical size of the crystallites, which, in turn, depends on the energy associated with the creation of the new phase and the interfacial free energy of the nucleated species with the liquid component. When the polar groups are close in proximity, the crystal packing arrangements are able to sequester these groups aw...