Elastomeric freely suspended membranes have been prepared via Langmuir−Blodgett transfer of cross-linked monolayers of polyisoprenes with anthracene side chains and sulfonate headgroups. The polymers, which have a chain length of approximately 540 repeat units and on average 8 anthracene side chains per polymer molecule, were spread at an air−water interface from chloroform/ethanol solutions and laterally compressed to an average area per molecule of 200 Å2. These monolayers were cross-linked via irradiation with UV light of wavelength 305−420 nm and then transferred to a brass plate with a circular hole of 0.4 mm diameter. The approximately 40 nm thick cross-linked monolayers completely covered the hole. It was possible to elastically deform the resulting suspended membrane by applying an overpressure from one side.

Hydrophobic polymers with low glass transition temperature (polyisoprenes) and a single head group (sulfonate) have been synthesized and characterized as insoluble monolayers on a water surface. The films are considerably thicker (10−50 nm) than conventional Langmuir monolayers of low molecular weight substances or polymers with surface-active repeating units. The thickness is inversely proportional to the area per head group. Films can be transferred via the Langmuir−Blodgett technique with transfer ratios close to 1. We use these monolayers as model systems to investigate the influence of the polymer chain statistics on the properties of solvent-free tethered polymers. We assume that each polymer chain is bound to the water phase with the head group and has the conformation of a distorted three-dimensional coil. The distortion increases with decreasing area per head group (A/n) and influences the isotherm of the polymer monolayers. We develop a theoretical description of this effect and conclude that, at a given area per head group, the surface pressure increases linearly with the chain length. In the case of Gaussian statistics, the slope of this line is proportional to the third power of the area per head group. In the case of non-Gaussian statistics, this slope can be expressed as a polynomial of A/n. The experimental data confirm these theoretical predictions. Deviations from Gaussian statistics can be neglected, and the description as a nonuniformly stretched brush (Semenov theory) comes closer to the experiment than the model of a uniformly stretched brush. Chains shorter than 300 repeat units systematically deviate from the theory.

Insoluble monolayers of hydrophobic polymers with low glass transition temperature (perfluoropolyethers, polyisoprenes) and a single ionic head group (carboxylic acid, sulfonate) have been characterized at the air/water interface via X-ray reflectivity measurements. The films are considerably thicker (30−420 Å) than conventional Langmuir monolayers of low molecular weight substances or polymers with surface active repeat units. The thickness is inversely proportional to the area per head group and is in accordance with a model assuming a solvent-free hydrophobic layer of the same density as the bulk material.

Dynamic light-scattering experiments with mixtures of non-critical composition of the nitrobenzene-isooctane system are carried out to obtain information about the temperature and composition dependence of the mutual diffusion coefficient, D. The system has a mixing gap with an upper critical point. It is shown that D decreases in a characteristic way along two pathways in the phase diagram of the system: approaching the temperature of phase separation in a mixture of constant composition or approaching the critical point along the two branches of the liquid-liquid coexistence curve. From a thermodynamic point of view this behaviour is interpreted as being caused by the temperature and composition dependence of the thermodynamic factor (8pj/8xJT, , , . An equivalent interpretation is based on the assumption that it is caused by the temperature and composition dependence of the correlation length of the local composition fluctuations. Evidence for the validity of the two interpretations is given. The described temperature and composition dependence of D appears to be a systemindependent property of binary liquid mixtures with a miscibility gap.