AFM based single molecule force spectroscopy was used for the investigation of single polyelectrolyte chains. Namely, the elasticity of polyvinylamine chains and their desorption from solid surfaces was studied as a function of the polymer's charge density and electrolyte concentration. Experimental force−distance profiles were fitted by the wormlike chain model, including elastic contributions arising from the stretching of bond angles and covalent bonds. It was found that, under the high stretching forces which can be applied in the AFM experiments, the bending rigidity of polyelectrolyte chains (as described by the persistence length) is significantly lower than predicted by Odijk−Skolnick−Fixman (OSF) theory. Furthermore, the desorption force of single physisorbed polymer chains from negatively charged silica surfaces was determined. In addition to the electrostatic interaction between polymer and substrate, which depends linearly on the Debye screening length and the polymer's line charge density, a constant nonelectrostatic contribution to the desorption force was observed.

In this study, tapping mode scanning force microscopy was applied to characterize the distribution and adsorption structure of poly(ethylenimine) (PEI) macromolecules adsorbed onto negatively charged polystyrene latexes as colloidal model systems and onto molecularly flat mica surfaces as reference systems. On both surfaces, PEI macromolecules can be reproducibly mapped by tapping mode AFM, yielding molecular resolution without sample degradation despite the only relatively weak noncovalent coupling of the polyelectrolytes to the substrate surface. We are able to quantify their lateral dimensions as a function of the corresponding molecular weight. The lateral dimension of the adsorbed PEI macromolecules (60 down to 20 nm) on both types of substrates are in fair agreement with the diameters as measured by dynamic light scattering for the respective molecules in solution. Their adsorption structure is patch-like flat in the dried state under ambient air. However, mica and polystyrene surfaces result in a large difference in the height of the adsorbed macromolecules, which we interpret as being due to the grossly different surface charge densities of the substrates. Quasi-elastic light scattering (QELS) on PEI-covered polystyrene latexes in solution yields essentially the same heights of the adsorbed macromolecules as found by AFM in the dried state in ambient air. This indicates that there is no appreciable collapse upon drying at ambient conditions and further backs the notion of a dense patchlike adsorption structure in solution. These findings are discussed with respect to implications for the flocculation mechanism relevant for PEI.

Today's shampoo formulations are beyond the stage of pure cleansing of the hair. Additional benefits are expected, e.g. conditioning, smoothing of the hair surface, improvement of combability and lather creaminess. Cationic polymers play an important role in providing many of those features. Therefore, within the last few years their use in shampoos has increased greatly. In the only last two decades, shampoo designation has gradually changed from '2-in-1' to '3-in-1' and then to 'multifunctional', as at present. The consumer demands products which live up to their promises. Modern shampoos contain a wide variety of ingredients such as co-surfactants, vitamins and pro-vitamins, protein derivatives, silicones, natural-based plant extracts and other 'active ingredients', but there is still a need for conditioning polymers. The specific objective of this study is to assess the conditioning efficacy of cationic polymers and to investigate their mechanisms in a shampoo system. The investigations were carried out on formulations that contained sodium lauryl ether sulphate and different cationic polymers, e.g. Polyquaternium 7, 10, 11, cationic guar gum and Luviquat Care (Polyquaternium 44), a new branched copolymer of vinylpyrrolidone (VP) and quaternized vinylimidazolium salts (QVI). We used test methods relevant to the applications in question, such as combing force measurements, the feel of the hair and the creaminess of the lather, to assess the efficacy. Atomic force microscopy and electrokinetics (streaming potential) were used to detect polymer residues on treated hair. All the polymers under investigation improved the overall performance of the shampoo formulations. This was demonstrated by means of combing force measurements, sensorial tests and analytical methods, namely zeta potential measurement and atomic force microscopy. Polyquaternium 44 exhibited the best conditioning properties on wet hair without sacrificing removability or absence of build-up. The latter are the most striking weaknesses of cationic Guar Gum-based polymers. Polyquaternium 10 can also be removed from the hair after rinsing with anionic surfactant but it does not perform as well as Polyquaternium 44 in the fields of wet combability and sensorial criteria such as lather creaminess and feel of the hair. We postulate that the outstanding properties of Polyquaternium 44 as a conditioning agent for shampoos are due to its tailor-made 'branched' structure. There is a clear correlation between the molecular weight and the efficacy of the new copolymers of VP and QVI. Only cationic polymers with a very high molecular weight are effective as conditioners in shampoos based on anionic surfactants. Surprisingly, they do not have to have a high cationic charge. On the basis of all our results, our postulation is that the polymer residue which is responsible for conditioning does not form a flat layer on the hair. Rather, the polymer residue adsorbs with the few cationic moieties, while the uncharged part of the polymer forms loops, which are orient...

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Modern water‐borne paints are applied in different areas ranging from high‐gloss lacquers to flat, scrub‐resistant interior paints. The pigment volume concentration (PVC) is one key‐parameter adjusting the application properties. In this work formulations differing in the type of binder and dispersing agent were investigated by various techniques concerning the distribution of pigments in the liquid paints and films. The structure of the paints was analyzed by Remission Light Spectroscopy (RLS), Disc Centrifugation, Cryo‐Replica Transmission Electron Microscopy (Cryo‐TEM) and Cryo‐Scanning Electron Microscopy (Cryo‐SEM). The pigment distribution in the films was examined by means of Atomic Force Microscopy (AFM), TEM and RLS. The tendency of the pigments to form aggregates was found to depend on both: the type of binder and the dispersing agent. Only by adjusting the properties of the binder in combination with common dispersants it is possible to get well distributed TiO2 particles within the paint. Correlation of application properties e.g. gloss and blocking to the microscopic structure is presented.