No abstract

No abstract

No abstract

The surface forces apparatus technique was used to measure the normal forces, thin film viscosity, and lateral (frictional) forces between two surfaces interacting across 4′-n-octyl-4-cyanobiphenyl (8CB), to determine the effects of confinement (film thickness) and shear (sliding velocity) on the ordering of the smectic-A and the nematic phases. The surface roughness and hydrophobicity were altered by different adsorbed surfactant monolayers to study the effects on the orientation and anchoring of 8CB. The positional order increases as the surface separation decreases, and the orientational ordering increases with increasing shear rate. The friction force in the planarly oriented nematic phase resembles results for alkanes, while the better ordered smectic-A phase exhibits lower friction forces. The liquid crystal orients perpendicularly to surfactant-coated surfaces. On a loose-packed surfactant layer, it becomes strongly anchored, which increases the resistance to sliding, while on a close-packed monolayer the friction force is low, but the liquid crystal is easily removed by the applied load or pressure.

The structure of polymer-decorated phospholipid monolayers at the solid-solution interface was investigated using neutron reflectometry. The monolayers were composed of distearoylphosphatidylethanolamine (DSPE) matrixed with varying amounts of DSPE-PEG (DSPE with polyethylene glycol covalently grafted to its headgroup). Mixed lipid monolayers were Langmuir-Blodgett deposited onto hydrophobic quartz or silicon substrates, previously hydrophobized by chemically grafting a robust monolayer of octadecyltrichlorosilane (OTS). We show that this method results in homogeneous and continuous phospholipid monolayers on the silanated substrates and determine that the grafted PEG chains extend away from the monolayers into the solvent phase as a function of their density, as expected from scaling theories. In addition, ligands were coupled to the end of the PEG chains and selective binding was demonstrated using fluorescence microscopy. Our results demonstrate that these constructs are ideal for further characterization and studies with well-defined monomolecular films.