Kinetics of Heterogeneous Nucleation of n-Alcohol Crystals from Solution Assisted by Template Thin Films of Monoacylglycerols and Fatty Acids

Abstract

Kinetic measurements have been made on heterogeneous nucleation of long-chain n-alcohol crystals (herewith referred to as guest crystals) from solution, which was accelerated by the presence of vapor-deposited thin films (referred to as templates) of monoacylglycerols and long chain fatty acids. The host templates were put in slightly supersaturated solution (decane solvent), in which no crystallization occurred over several hours without the template films, yet the template films accelerated the crystallization within several minutes of induction times. The crystallization behavior was examined by microscopic observation and induction time measurements, with specific attention to the template−guest relationships in terms of polymorphism, molecular orientation, and chain length limitation. It was confirmed that the host template films of the monoacylglycerols and the fatty acids accelerated the nucleation of the n-alcohol crystals, exhibiting the polymorphic matching, preservation of the molecular orientation, and the chain length matching. However, remarkable differences were revealed in the kinetics of heterogeneous nucleation between the host templates of monoacylglycerols and fatty acids; e.g., the monoacylglycerol templates accelerated two or three times more than the fatty acid templates under the same supersaturation conditions. This difference was ascribed to the specific host−guest interactions between the template and the guest materials as revealed in the phase behavior of the binary mixtures in the bulk state: monoacylglycerols and n-alcohols exhibited molecular compound formation, whereas eutectic phases are formed between fatty acids and n-alcohols. It was inferred that the template−solute interactions through van der Waals forces and hydrogen bonding at the interfaces of the template films and solution are differently operative in the two sets of the thin film templates and the guest materials.