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Surface-bound layers of poly(l-glutamic acid) prepared by a recently described “grafting-from” method¹ were analyzed with respect to electrical charging and structural alterations upon variation of pH and concentration of the background electrolyte in aqueous solutions. The microslit electrokinetic setup (MES)^2,3 was utilized for the combined determination of zeta potential and surface conductivity on the basis of streaming potential and streaming current measurements at polypeptide layers in contact with aqueous electrolyte solutions of varied composition. In situ ellipsometry was applied at similar samples immersed in identical aqueous solutions to investigate the influence of the solution pH on the structure of the polypeptide layers. Zeta potential and Dukhin number versus pH plots revealed the dissociation behavior of the surface-bound polypeptides indicating a significant shift of the pK of their acidic side chains correlating with the concentration of the background electrolyte potassium chloride and the related variation of the Debye screening length. Surface conductivity data pointed at a more expanded structure of the polypeptide layer in the fully dissociated state as an increased ion conductance in this part of the interface was determined. The occurrence of a strong increase of the thickness and a corresponding decrease of the refractive index for the coil state of the layer strongly supports the findings of the electrokinetic measurements. This fully reversible “switching” of the layer structure was attributed to helix−coil transitions within the grafted polypeptides induced by the dissociation of carboxylic acid functions of the polypeptide side chains. The shift of the “switching pH” of the surface-bound poly(l-glutamic acid) layers at varied concentrations of the background electrolyte was interpreted as a result of the pK shift of the carboxylic acid groups of the polypeptide side chains. The observed patterns prove that the electrostatic interactions causing this shift occur within but not between the grafted chains.

The transition of crystal growth is revealed in ultrathin poly(ethylene oxide)/poly(methyl methacrylate) (PEO/PMMA) blend films (film thickness D < 3 nm) as the crystallization condition changes from vacuum to humidity. The PEO crystallizes into a fractal-like branched structure in a vacuum from a state mixed with PMMA, but in humidity into one reminiscent of dense branching morphology (DBM). The crystal lamellae in both conditions orient flat-on, but the DBM-like structure is much thicker and wider, indicating a crystallization more close to equilibrium. Results show that as a PEO/PMMA blend film is exposed to humidity, PEO chains demix with PMMA and segregate on a PMMA layer before or during crystallization. The crystal growth transition is attributed to the change in the factors that dominate the crystal growth at crystal growth fronts, that is, the kinetic and surface tension effects, as a result of changing the polymer states in the blend films. The crystal growth of the demixed PEO on the PMMA layer is dominated by a strong surface tension effect, while crystal growth of PEO in a blend/mixed state is dominated by either a kinetic effect or a weak surface tension effect depending on the film composition. The compositional dependence of the crystal growth in humidity is also elucidated on the basis of the changing of polymer states in the films.

Polymeric/inorganic nanocomposite dishes of hydrolyzed poly(styrene-alt-maleic anhydride) (HSMA) and TiO2 were patterned on substrates by microcontact printing (μCP) of the dispersions of nanosized TiO2 colloidal particles in HSMA solutions; the structure formation with respect to the μCP process was discussed. The orderly arranged HSMA/TiO2 dishes are homogeneous in size. After removal of the polymer in the printed composite dishes by calcination, well-defined nanostructured TiO2 layers are formed in the regions where the composite dishes appear. The printed composite dishes come from the dishlike composite aggregates transferred onto a substrate from a stamp surface. The drying of the dispersion droplets formed in a topographically controlled de-wetting of the dispersion on the stamp surface results in the dishlike aggregates, for which the pinning of the droplet contact line is of key importance. The diameter of the printed dishes is mainly determined by the stamp geometry, and not influenced remarkably by HSMA and/or TiO2 concentrations. The component fractions mainly influence the heights of the dish rim and plate, the width of the dish rim, and the continuity of the plate within the rim.

Defects in Distyrylpyrazine (DSP) monomer crystals haven been investigated by Transmission Electron Microscopy (TEM), light microscopy and synchroton topography. The onset of the photoreaction causes a multiplication of the defects. The course of the photoreaction as well as the product and stress distribution in the crystal are strongly wavelength dependent. Fracture of the crystals can be prevented under special irradiation conditions. A crystal structure analysis of a photoproduct in a four-center-type photopolymerization is available now for the first time. The chemical composition of these crystals has been determined by gelpermeation chromatography (GPC). The results are discussed with respect of the solid state reaction mechanism.