Several rodlike 4,4‘‘-bis(decyloxy)-p-terphenyl derivatives incorporating nonionic hydrophilic groups in the lateral 2‘-position (2-oxa-4,5-dihydroxypentyl, 2,5-dioxa-7,8-dihydroxyoctyl, 2,5,8-trioxa-10,11-dihydroxyundecyl, and 2,5,8,11-tetraoxa-13,14-tetradecyl groups) and 2‘-(2-oxa-4,5-dihydroxypentyl)-4,4‘‘-diundecyl-p-terphenyl form well-ordered thin films when spread at the air−water interface. One observes two sharp breaks in the pressure/area isotherms separated by a large plateau. The first break occurs at an area of ca. 0.90 nm2/molecule, an area which corresponds to a side-on arrangement of the terphenyl units at the interface. The plateau corresponds to a first-order phase transition. The surface pressure related to this transition significantly rises with an increasing number of oxyethylene units in the hydrophilic lateral groups. Brewster angle microscopic investigations indicate the formation of fluid domains in this region. In some cases these domains coalesce to a homogenous layer. The surface potential is nearly constant in the region of the plateau, which can be explained by a defined collapse due to the formation of a triple layer consisting of a bilayer on top of the monolayer.

Methyl arachidate Langmuir-Blodgett multilayers, built up by X-, XY-and Y-type transfers, are characterized by means of contact angle measurements, and optical and atomic force microscopy under ambient conditions. Contact angle investigation shows identically high hydrophobicity of the surfaces produced by X-and Y-type depositions, implying molecular overturning during the X-type transfer. This overturning has not been detected in the previous X-ray study of small numbers of deposited fatty acid methyl ester monolayers. Molecular resolution AFM images of thin methyl arachidate LB films show a disordered surface structure. Scanning over larger film regions reveals a considerable difference in the surface morphology, corresponding to pure and mixed-type LB transfers. Reorganization of the multilayers occurs under ambient conditions in both cases. Larger aggregates, steps, and irregular islands are found with Y-type deposition. Ester LB films studied in an aqueous environment rearrange more easily than those stored in air. AFM imaging of the "contact line corrosion" of the multilayers shows a collective depletion of the whole LB film from the substrate at the wetting perimeter. The instability of the ester mono-and multilayers is explained on the basis of the intra-and interlayer molecular interactions within the spread and the deposited films, and by their weak adhesion to the substrate,

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A Langmuir−Blodgett multilayer film of cadmium arachidate and a complex multilayer system of cadmium stearate bilayers separated by copolymer interlayers have been prepared by sequential transfer of deuterated and nondeuterated bilayers on a solid support. They were investigated at different temperatures using X-ray and neutron specular as well as diffuse reflectivity measurements. The neutron scattering was used to determine the vertical arrangement of deuterated chains within the multilayers and to study the different roughnesses at the chain−chain and chain−metal ion interface separately. The specular reflectivity patterns of both samples could only be interpreted considering the contribution of resonant−diffuse scattering caused by the perfect vertical correlation of individual interface roughnesses within a certain domain. For the two samples the superstructure peak intensity appearing in the respective neutron reflectivity curve decreases dramatically during annealing between 50 and 65 °C. This indicates an intermixing of deuterated and nondeuterated molecules within the film. The molecular exchange cannot be suppressed by the incorporation of copolymer interlayers between the deuterated and nondeuterated chains. Because the X-ray reflectivity patterns remain nearly unaffected by the annealing and because the annealing temperature was lower than the melting point of the pure fatty acid phase (about 70 °C), we interpret this effect by a vertical movement of fatty acid molecules across the still lamellarly stacked framework of fatty acid salt molecules. The temperature dependence of this process shows Arrhenius-like behavior. For both samples the estimated activation energy is 1.7 ± 0.5 eV (164 ± 48 kJ/mol) and is assigned to the van der Waals bonding energy of single molecules in a 2D hexagonal lattice. From time-dependent measurements we estimated a vertical diffusion coefficient in the order of 10-22 m2/s.