Physical Chemistry Chemical Physics

Mahltig, Boris; Walter, Harald; Harrats, Charef; Müller-Buschbaum, Peter; Je′rôme, Robert; Stamm, Manfred

doi: 10.1039/a903395epmid: N/A

Polyampholytes are macromolecules that contain oppositely charged groups. We have studied the adsorption of the polyampholyte diblock copolymer poly(methacrylic acid)--poly((dimethylamino)ethyl methacrylate), PMAA--PDMAEMA, on oxidized silicon surfaces. The amount of polymer adsorbed from aqueous solution of different pH and salt concentration was measured by ellipsometry. The influence of the added salts NaCl, NaSO and CaCl was determined. In every case adsorption took place, although the polyampholyte and the substrate exhibit the same sign of net charge. For all types of salt, the adsorbed amount shows two maxima close to the isoelectric point (IEP) of the polymer as a function of pH. Directly at the IEP of the polyampholyte, no adsorption was found. The measured dependences can be explained by the adsorption of one or the other of the two blocks depending on acidity and ionic strength. Furthermore, the lateral structure of the dried films was investigated by scanning force microscopy (SFM).

Müller-Buschbaum, P.; S. Gutmann, J.; Stamm, M.

doi: 10.1039/a903012cpmid: N/A

The dewetting behavior of thin, deuterated polystyrene (dPS) layers on silicon surfaces is investigated. The surface topographics thus produced are investigated with scanning force microscopy and with grazing incidence small angle scattering. Neutrons and X-rays interact differently with this system, producing a reverse of the scattering contrast in the investigated system dPS–Si. For samples annealed above their glass transition temperature a difference in the evolved surface structures is detected as compared with samples stored under toluene vapor. Confined thin films, with a thickness below one-third of the radius of gyration of the unperturbed molecule </3, dewet irrespective of the applied sample treatment. Thin, but non-confined samples stay stable during annealing, whereas they dewet in a toluene vapor atmosphere.

Frank, Jochen; Simon, Frank; Schmitt, Franz-Josef

doi: 10.1039/a903285apmid: N/A

The interfacial properties of a rubber blended polypropylene were investigated by the combination of complementary techniques in order to characterize the effects of different surface treatments. The wettability was investigated by contact angle measurements with water, streaming potential measurements indicated the Brønsted acidity/basicity of the surfaces, and X-ray photoelectron spectroscopy (XPS) identified the chemical elements, which were incorporated by the various treatments. The topography and the roughness of the samples were quantitatively analyzed by scanning force microscopy (SFM). Direct force measurements showed the possibility of changing the sign of the surface charge by choosing suitable buffer solutions, leading to attraction and repulsion to the SiN tip, respectively. In the case of technical-type polymer samples used in this study, direct force measurements are in exact agreement with the streaming potential measurements and offer a valuable tool for interface characterization.

DuChesne, Alexander; Bojkova, Albena; Rottstegge, Jörg; Glasser, Gunnar; Neher, Dieter; Krieger, Stefan

doi: 10.1039/a903095fpmid: N/A

The influence of latex morphology, composition and drying conditions on film formation and film properties is investigated for heterogeneous poly(acrylate) latex model systems. For blends of small latex particles water evaporation is the rate limiting process of film formation and the critical hard phase content reaches theoretical predictions. Upon increasing the size of the particles, their deformation becomes rate limiting which results in lower critical hard phase content, which significantly depends on film thickness. Film forming properties of blends are compared with that of heterogeneous lattices possessing different morphology. According to conventional measurements of the minimum film forming temperature, core-shell lattices with a glassy (high ) shell are non-film forming. A more thorough investigation reveals significant differences depending on latex composition and even film formation. It is demonstrated that this film formation is rate limited by particle deformation. Electron microscopy, turbidity measurements, electromechanical testing and interferometrical thickness determination are used to investigate film densification and particle deformation. Solid state NMR spin diffusion measurements are applied to characterize morphological changes during film formation and interdiffusion.

Pasch, Harald

doi: 10.1039/a902365hpmid: N/A

Complex polymers are distributed in more than one way in terms of molecular heterogeneity. In addition to the molar mass distribution, they are frequently distributed with respect to chemical composition, functionality, and molecular architecture. For the characterization of the different types of molecular heterogeneity it is necessary to use a wide range of analytical techniques. Preferably, these techniques should be selective towards a specific type of heterogeneity. The combination of two selective analytical techniques is assumed to yield two-dimensional information on the molecular heterogeneity.The present article discusses the principles of combining different analytical techniques in multidimensional analysis schemes. The most promising protocols for coupled techniques are the combination of two different chromatographic methods and the combination of chromatography and spectroscopy. This article reviews the basic principles of two-dimensional chromatography combining interaction chromatography and size exclusion chromatography. In the use of liquid chromatography with selective detectors, the coupling of different chromatographic techniques with Fourier-transform infrared and nuclear magnetic resonance spectroscopies and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry is highlighted.

Hädicke, Erich; Rieger, Jens; Ursula Rau, Iris; Boeckh, Dieter

doi: 10.1039/a903949jpmid: N/A

The precipitation of CaCO during washing treatments can be reduced by polymeric additives. This process of incrustation inhibition could be described by modeling the effects upon crystal growth. Molecular dynamics calculations were used. Different conformations of the additives on the substrates developed during the time course of these simulations. The interaction energies of the additives with the substrates and the deformation energies of the additives on the main growth faces of calcite enabled conclusions to be drawn on the efficiency of the additives for incrustation inhibition. In addition, information on the mode of action was derived from the dynamics of the additives on the calcite faces. Although no quantitative results were obtained with the simplified models, trends in efficacy could be uncovered from the differences in the results. An acrylate/maleate copolymer and an oligomaleate were investigated as model systems. The interaction of the two studied additives with the positively charged calcite {1 1̄0} face are significantly stronger than with the neutral calcite {1 0 4} face. Both additives are more mobile on the {1 0 4} face than on the {1 1̄0} face. The dynamics of different polymer chain segments during the course of the molecular dynamics runs show different features. Whereas the carboxy groups at the ends of the chain are very mobile the groups in the middle of the chain are more firmly adsorbed to the crystal surface. Chain segments in the middle of the chain will therefore hinder the crystal growth more effectively than end segments. The additives are deformed during their adsorption to both faces of calcite. The respective deformation energies of the additives are much smaller than the adsorption energies of the additives to the calcite faces. The acrylate–maleate copolymer adsorbs significantly stronger to the calcite faces than oligomaleate. This is due to the higher additive/substrate interaction energies and the larger number of contacts between the carboxy groups of the additives and the Ca atoms of the substrate in the case of the acrylate–maleate copolymer, in comparison with oligomaleate. The studied additives can disperse different amounts of CaCO in water. The measured calcium carbonate dispersion capacity is higher for the acrylate–maleate copolymer than the oligomaleate.

Wulf, M.; Michel, S.; Jenschke, W.; Uhlmann, P.; Grundke, K.

doi: 10.1039/a903282gpmid: N/A

By employing a new strategy presented recently by Wulf ., axisymmetric drop shape analysis (ADSA) can be used to determine simultaneously the surface tension and the density of polymer melts from sessile drops at elevated temperatures. This required the modification of the ADSA algorithm to replace the density by the mass of the drop as input parameter and the development of a closed high temperature chamber whose temperature can be precisely controlled. In addition, special sample holders for the formation of pendant and sessile drops at elevated temperatures were needed. Recently, their design has been improved, which is described in this paper. For a commercial epoxy resin (DER 664 UE), it is shown that measurements with sessile drops yield essentially the same surface tension values and temperature coefficients as with pendant drops. The densities determined with ADSA are comparable to independent results.

Zipfel, Johannes; Berghausen, Jörg; Schmidt, Gudrun; Lindner, Peter; Alexandridis, Paschalis; Tsianou, Marina; Richtering, Walter

doi: 10.1039/a904014epmid: N/A

The influence of shear on the mesoscopic structure in the lamellar region of ternary poly(ethylene oxide)–b-poly(propylene oxide)–b-poly(ethylene oxide) block copolymers PEO–b-PPO–b-PEO and PEO–b-PPO–b-PEO (Pluronic P123 and F127)/water/butanol systems was investigated by different techniques namely: small angle neutron and light scattering (SANS, SALS), as well as birefringence. A transition from parallel to perpendicular alignment of lamellae, with a corresponding decrease in the viscosity, was found with increasing shear rate at high block copolymer concentrations. However, a shear-induced formation of multilamellar vesicles (“onions’') was observed when the polymer concentration was reduced.

Urban, Claus; Schurtenberger, Peter

doi: 10.1039/a903906fpmid: N/A

Colloidal systems are a subject of great interest in soft condensed matter research as well as in industry. But the ability to characterize colloidal systems with dynamic light scattering (DLS) is in general limited to systems with negligible contributions from multiple scattering of light. Therefore a variety of systems is excluded from investigations with DLS at high concentration and therefore increased turbidity. Often these samples were investigated under high dilution with, at least for some systems, a high probability of measuring artefacts. A promising solution to this problem consists of suppressing multiple scattering in a DLS experiment with a cross-correlation technique. Therefore we developed a so-called 3d cross-correlation instrument which enables us to characterize extremely turbid suspensions. After having found that the instrument works very well with model systems, we now demonstrate that complex ‘real world’ systems can successfully be characterized using this technique. An investigation of milk shows a strong dependence of the measured particle size distribution upon dilution. With the 3d instrument, however, the undiluted milk can be measured and artificial changes of the sample properties can be excluded.

B. Aberle, L.; Staude, W.; Hennemann, O.-D.

doi: 10.1039/a903167gpmid: N/A

The correct interpretation of light scattering data requires knowledge of the extent to which multiple scattering contributes to the measured signal. Generally, this information cannot easily be obtained in conventional light scattering experiments. We demonstrate the difficulties which arise with this problem by experiments with scatterers where the differential scattering cross section does not exhibit scattering minima. We investigate the influence of multiple scattering by performing combined static and dynamic light scattering experiments using the 3D cross correlation technique. We discuss that, despite the increase of the intensity ratio of multiply to singly scattered light with increasing scattering angle, the dynamic properties are more strongly affected for small scattering angles.