Low-Dimensionality Effects in the Melting of a Langmuir−Blodgett Multilayer

Abstract

Low-dimensionality effects in the melting behavior of a cadmium arachidate Langmuir-Blodgett multilayer have been studied. Depth resolved information about structural changes occurring with temperature is obtained using in-plane X-ray diffraction under standing wave conditions. The surface region exhibits a distinctly different melting behavior as compared to the bulk of the film. While in the bulk of a 13-monolayer cadmium arachidate multilayer, the crystalline phase directly transforms to a tilted hexaticlike phase at 360 K, in the near surface region transformation occurs via an intermediate smectic phase. This behavior of the surface region is similar to that observed in two-dimensional crystals. Thus even in a thick Langmuir-Blodgett multilayer, the surface region exhibits low-dimensionality effects.

Role of substrate in melting behavior of Langmuir–Blodgett films

“…The assignment of diffraction peaks is (01 11)  and (10) of distorted hexagonal lattice structure, in conformity with earlier works [32][33][34]. This rapid decrease in Δγ signals transformation to a hexaticlike phase [32][33][34]. The results…”

“…Further, existence of an intermediate smectic or nematic phase inserted between solid and hexatic phases in a system with a distorted hexagonal symmetry, as predicted by theory, has also been observed [7,35]. Even in thick films of cadmium arachidate, low dimensionality effects have been observed in the surface region [33], while CdA LB film of same thickness confined between two metallic layers shows a lack of additional smectic phase [34]. Before melting transition the distorted hexagonal lattice structure of CdA LB film transform to hexaticlike phase with increasing temperature [32][33][34].…”

“…In literature distorted hexagonal lattice structure of Cd arachidate multilayer has been reported [7,[32][33][34]. Existence of a hexaticlike phase has been clearly evidenced in such studies.…”

“…Even in thick films of cadmium arachidate, low dimensionality effects have been observed in the surface region [33], while CdA LB film of same thickness confined between two metallic layers shows a lack of additional smectic phase [34]. Before melting transition the distorted hexagonal lattice structure of CdA LB film transform to hexaticlike phase with increasing temperature [32][33][34].…”

Temperature-Induced Transitions in the Structure and Interfacial Rheology of Human Meibum

“…However, the water interface can still influence meibum organization. Even in thick multilayer films, the layers nearest the interface can show low-dimensionality behavior, or organization induced by contact with the interface (41). Therefore, both the interfacial and bulk properties reported here will be relevant to the lipid layer of the tear film, and we expect that melt transitions and physical structures of meibomian lipids in the lipid layer of the tear film will lie somewhere between those of bulk meibum and interfacial films.…”