Untersuchungen zu Wechselwirkungen von Tensiden, Polymeren und Farbstoffen in Lösung und an Grenzflächen

In order to elucidate the influence of surfactants and DTI polymers on dye transfer, the study of the molecular interaction between surfactant, polymer and dye in solution and at interfaces was addressed to evaluate the molecular mechanism of surfactant and DTI polymer in dye transfer inhibition (DTI), especially for critical polyamide dyes. The adsorption structures of single components and of binary mixtures of the dye Acid blue 113, the nonionic surfactant alkyl heptaglycolether (C12-18E7) as well as the anionic surfactant sodium dodecyl sulfate (SDS) and the DTI polymer poly(vinylpyrrolidone-vinylimidazole) (PVPVI) on the model surface graphite were identified by atomic force microscopy (AFM) in liquid for the first time. In addition, the adsorption of the dye and the dye in mixture with SDS at the carbon black-solution interface was analyzed in comparison with AFM studies. In order to present structural models for the systems investigated, the interaction of these components in solution was additionally studied by UV-Vis spectroscopy and dynamic light scattering (DLS) and the interaction at the air-solution interface was determined by surface tension measurements. In summary, AFM proves to be a very powerful tool to characterize the adsorbed layers from binary aqueous mixtures of dye, surfactant and DTI polymer at solid-liquid interfaces. It enables the identification of adsorption structures on the nanometer scale and allows the allocation of individual components. The studies on nonpolar model surfaces reveal that two different mechanisms play a decisive role in the adsorption of dye on surfaces in the presence of surfactants: the competitive adsorption of individual components and the incorporation of dyes into micellar surfactant aggregates on model surfaces. C12-18E7 has a higher adsorption preference than the dye to model surfaces, and on the other hand, the dye can be incorporated into surfactant micelles in solution as well as into surfactant aggregates adsorbed on surface, which can result in additive or adverse effects of the two mechanisms on dye transfer inhibition. In comparison with the anionic surfactant SDS, the nonionic surfactant C12-18E7 shows a greater effect due to its higher affinity for model surfaces and stronger incorporation of the dye into surfactant micelles in solution. The DTI polymer PVPVI forms a dye-polymer complex with the dye on model surfaces above the CAC of the polymer, as also shown in solution. In the presence of surfactants (> CMC), the adsorption of the polymer onto surfaces is inhibited due to the dominant adsorption of surfactants. In this work, adsorption mechanisms were identified to get an in-depth understanding of the influence of surfactant and DTI polymer on dye transfer at a molecular level for a hydrophobic model surface. Based on these fundamental results, further studies on textile or textile-like surfaces would give additional insights in the mode of action of DTI in real washing processes.