The lateral stresses that latex dispersions undergo upon forming films have been investigated by an optical lever technique. Dilational lateral stress induced by capillary pressure, tensile stress caused by the uniaxial shrinkage imposed by the substrate, and stress relaxation on longer time scales were observed. Failure of film formation because of cracking events was reflected in irregular substrate deflection. The stress evolution in pigment-filled paints below the critical pigment volume concentration displayed two maxima in tensile stress which we associate with a separation of time scales between the drying of polymeric binder and the particle rearrangement to eliminate voids.

No abstract

A structural concept for nonlinear optical (NLO) polymeric materials optimized for long-term stability of the polar order is presented:  rigid-rod-like main chain polymers furnished with long alkyl side chains with a portion of the side chains being replaced by NLO-active chromophores were synthesized. The chromophores are rigidly attached to the main chains, normal to the direction of the polymer backbone. In this particular geometry the motion of the NLO-active chromophores is restricted to a two-dimensional rotation around the stiff main chain. X-ray diffraction experiments on spin-cast films of the polymers show a lamellar structure with a preferential orientation of the layers parallel to the substrate plane. The incompatibility of polar main chains and nonpolar side chains leads to this microphase segregation. This layered structure improves the long term stability of polar order in the poled polymer film. Dielectric spectroscopy revealed only one relaxation process of large dielectric strength. The Arrhenius-type temperature dependence of relaxation times indicates a locally activated motion of the chromophores.

Various latex dispersions based on poly(vinyl acetate) stabilised by different surfactants and polyelectrolytes were investigated by NMR methods to elucidate the macroscopic and molecular film‐formation process of these latex dispersions. Macroscopically, the inhomogeneous drying in the film‐formation process was investigated by NMR‐imaging techniques. Here the influence of different amounts of surfactant on the homogeneity of the drying process was monitored. The molecular film‐formation process was investigated by 1H, 2H, and 13C solid‐state NMR spectroscopy. For these bulk measurements, films of latex dispersions were homogeneously dried to different defined solid contents. Spectroscopic analysis allows the investigation of the drying process of the water at different solid contents with a pronounced influence on the polymer/water interface and the latex particle core. The film‐formation process is correlated to the drying mechanism of different types of water within the film. External water, water at ionic and non‐ionic groups at surfactants in the polymer/water interface, and water in the swollen and mobilised polymer, could be distinguished during the drying process.