Kinetics of heterogeneous nucleation of n-alcohol crystals from solution assisted by template thin films of monoacylglycerols and fatty acids

Kinetic measurements have been made on heterogeneous nucleation of long-cha in,n-alcohol crystals (herewith referred to as guest crystals) from solutio n, which was accelerated by the presence of vapor-deposited thin films (ref erred to as templates) of monoacylglycerols and long chain fatty acids. The host templates were put in slightly supersaturated solution (decane solven t), in which no crystallization occurred over several hours without the tem plate films, yet the template films accelerated the crystallization within several minutes of induction times. The crystallization behavior was examin ed by microscopic observation and induction time measurements, with specifi c attention to the template-guest relationships in terms of polymorphism, m olecular orientation, and chain length limitation. It was confirmed that th e host template films of the monoacylglycerols and the fatty acids accelera ted the nucleation of the n-alcohol crystals, exhibiting the polymorphic ma tching, preservation of the molecular orientation, and the chain length mat ching. However, remarkable differences were revealed in the kinetics of het erogeneous nucleation between the host templates of monoacylglycerols and f atty acids; e.g., the monoacylglycerol templates accelerated two or three t imes more than the fatty acid templates under the same supersaturation cond itions. This difference was ascribed to the specific host-guest interaction s between the template and the guest materials as revealed in the phase beh avior of the binary mixtures in the bulk state: monoacylglycerols and n-alc ohols exhibited molecular compound formation, whereas eutectic phases are f ormed between fatty acids and n-alcohols. It was inferred that the template -solute interactions through van der Waals forces and hydrogen bonding at t he interfaces of the template films and solution are differently operative in the two sets of the thin film templates and the guest materials.