FROM 2-DIMENSIONAL MODEL NETWORKS TO MICROCAPSULES

The tensio-active properties of different types of diesters can be used to synthesize two-dimensional model networks at the interface between oil and water. We have systematically studied rubber-elastic. glass-like and transient membranes which are stabilized and crosslinked by physical or chemical contacts. The adsorption process of the monomeric diesters was investigated by measuring the interfacial tension at the boundary between oil and water. The experimental results can be interpreted on the basis of the '' Szyskowski ''- equation which holds for monomolecular films under ideal conditions. From the measured values of the interfacial tension it is possible to determine the surface concentration. The polymerization process occurs through radical-reactions which can be initiated by UV-irradiation. We have systematically studied the kinetics of surface gelation by measuring the two-dimensional shear modulus as a function of the reaction time. The experimental results can be interpreted in the framework of simple reaction mechanisms. The quantitative analysis of the experimental data allows to evaluate many details, of the photo-reaction as the free radical concentration, the number of linear chains and the rale constant of the cross-linking process. The two-dimensional sol-gel transition can easily be described in the framework of percolation theories which were proposed by Stauffer and de Gennes. According to these models, one expects to find a steep increase in the elastic modulus alter passing the gel point. The two-dimensional percolation exponent, determined in our experiments, agrees very well with the calculated result of 4/3. This holds for rubber-elastic and glass-like membranes. Rubber-elastic, cross-linked films exhibit interesting features, which can be explained by simple models. The shear modulus depends upon the surface concentration of elastically effective chains. The interfacial polymerization is not restricted to flat surfaces, and the corresponding films can be used for the stabilization of different types of emulsions. Oil droplets which are surrounded by cross-linked membranes. form simple systems which exhibit interesting properties of biological cells. The microcapsules can, for instance, be used in order to simulate blood flow in living vessels. We have measured the deformation process and the aggregation behavior of these microcapsules in Couette flow under a microscope, and we have investigated the influence of the membrane elasticity on the flow behavior of these emulsions. The data. thus obtained. can be compared with the particle behavior of rigid spheres and deformable liquid drops. The rheological properties of these artificial cells are useful to get a clearer picture of the complicated flow processes which occur in biological systems.