Evidence of a tilted and herringbone structure in cadmium behenate Langmuir–Blodgett ultrathin films: Comparison with Langmuir monolayers

Sliding behavior of liquid droplets on tilted Langmuir-Blodgett surfaces

The sliding behavior of liquid droplets on inclined Langmuir-Blodgett surfaces was investigated. The critical sliding angle defined as the tilt angle of the surface at which the drop slides down as well as the advancing and receding contact angles was measured for five different liquids on five surfaces. In addition, the contact line geometry was analyzed at critical sliding angle. The experimental relationship between the surface tension forces resulting from contact angle hysteresis and the weight of the drop was compared to theoretical predictions. Even though the shape of the drop bases was found as skewed ellipses, a model assuming parallel-sided elongated drops is shown to describe reasonably the experimental values. This result probably indicates the main influence of the capillary forces at the rear and front edges of the drop with respect to that exerted on the lateral sides.

The structure of ultrathin Langmuir-Blodgett films of cadmium behenate

Grazing incidence x-ray-diffraction investigations of the structures of Langmuir-Blodgett films of cadmium behenate with 1, 2, 3, 5, and 21 monolayers are reported. The single monolayer film, deposited on a hydrophilic substrate, showed a hexagonal structure, whereas the bilayer film, deposited on a hydrophobic substrate, had a rectangular structure with herringbone orientation of the acyl chains. With multilayer films formed on a hydrophilic substrate, it was possible to detect that the hexagonal structure of the first layer was retained when additional layers were deposited and that the additional layers had the same rectangular structure as the bilayer.

Variation of the in-plane structure with depth revealed by grazing incidence x-ray diffraction in a thin Langmuir-Blodgett film

Grazing incidence x-ray diffraction is used to characterize the molecular arrangement of ultrathin Langmuir-Blodgett (LB) multilayers. Using two angles of incidence of the beam allowing its penetration either throughout the complete depth of the film or only through the external layers, we show that it is possible to discriminate between the molecular packing of the deeper monolayers and that of the external monolayers of the LB film.