Measurement of the interactions between two ordering surfaces under symmetric and asymmetric boundary conditions

Abstract

With a surface forces apparatus we have measured the interaction between two surfaces immersed in the isotropic and the nematic phases of a lyotropic solution near its lamellar phase. A smectic ordering shows up near walls, giving a specific oscillatory force profile that is shown to be the sum of two contributions. The oscillations are the elastic response of the stack mechanically constrained by the confinement. The shape of the base line supporting the oscillations derives from the distribution of the smectic ordering between the two walls. In the case of fixed symmetric boundary conditions, the background is always attractive. However, under fixed asymmetric boundary conditions, the background turns out to be repulsive at short separations and becomes even repulsive at every separation when one of the two surfaces does not induce any order. ͓S1063-651X͑96͒08707-7͔

Theoretical Models for Surface Forces and Adhesion and Their Measurement Using Atomic Force Microscopy

“…Richetti et al [317] suggested a similar equation to describe the interaction between two surfaces across a smectic liquid, studied with AFM [318]. …”

Force measurements with the atomic force microscope: Technique, interpretation and applications

“…(8.2) is that the jump distance observed for the inner layer (which is the one being squeezed out last) is supposedly smaller than the distances between the other layers. Based on a model of de Gennes [739], Richetti et al [740] suggested an almost similar equation to describe the interaction between two surfaces across a smectic liquid. It was used to analyze AFM results [741].…”

Forces in nematic liquid crystals: from nanoscale interfacial forces to long-range forces in nematic colloids

“…when the fluctuation effects are neglected) were considered by a number of authors (7-11), and many interesting predictions were made, including surface-induced capillary condensation of the nematic phase (7-8) and pseudo-Casimir effect in liquid crystals, where the interaction is generated by fluctuations of the liquid crystalline order (12). The pioneering experimental work on structural forces in the nematic liquid crystals has been done by Horn et al (13) using a SFA, which was later continued by a number of authors (14)(15)(16)(17). A lot of work on lyotropic liquid crystals has been done on presmectic interaction (16,17) and capillary condensation of lamellar lyotropic phases (18)(19).…”

“…The pioneering experimental work on structural forces in the nematic liquid crystals has been done by Horn et al (13) using a SFA, which was later continued by a number of authors (14)(15)(16)(17). A lot of work on lyotropic liquid crystals has been done on presmectic interaction (16,17) and capillary condensation of lamellar lyotropic phases (18)(19).…”