Inhalt des Dokuments
Surface induced ordering of colloidal particles
- © AG v. Klitzing
When dealing with structures or particles on the nanoscale, forces that are relevant in the macroscopic world like gravity lose their importance when compared to electrostatic or surface forces. The latter ones usually are stronger than their, for example gravitational, counterpart by orders of magnitude. A decrease of the feature size goes along with an increase of the surface to volume ratio. Therefore, chemistry and physics on the nanoscale are closely related to the surface properties of the materials studied. The research is aimed at understanding how nanoparticles interact at interfaces which is relevant for material science (e.g. foams and surface patterning) as well as subject of fundamental research.
Contact: Adrian Carl, Züleyha Yenice
Carl, A. & von Klitzing, R. Smart Foams: New Perspectives Towards Responsive Composite Materials. Angew. Chem. Int. Ed., 2011, 50, 11290-11292
Complex fluids as decontamination media for hydrophobic solid surfaces
The implementation of new and biocompatible decontamination media is desired to efficiently decontaminate urban and natural environment in case of intentional or accidental release of highly toxic compounds. These decontamination media have to extract the contaminant out of sorptive surfaces, solubilize and convert the contaminant into non-toxic products. At the same time, these decontamination media must be non-corrosive and environmentally compatible.
- © AG v. Klitzing
Figure 1: a) Phase diagram (fish-cut) of a microemulsion system measured as a variation of surfactant content and temperature or cosurfactant at constant oil to water ratio. b) Schematic representation of microemulsion structures. c) Cryo-SEM image of a bicontinuous microemulsion structure. This microemulsion structure is observable in the one phase region close tot he „X“ point.
In this context, biodegradable and biocompatible microemulsions based on alkyl polyglucoside surfactants and food grade oils have attracted increasing interest (Figure1). Such microemulsions are promising liquid decontamination media due to their structural stability in a wide temperature range and their “green” and mild performance. The main advantage of microemulsions is their ability to extract and solubilize lipophilic contaminants in the oil phase, and simultaneously degraded the contaminant into non-toxic products across the amphiphilic interface by means of active agents solubilized in the water phase (Figure2). For example, it has been demonstrated that the enzyme Diisopropyl fluorophosphatase can efficiently detoxify highly toxic organophosphate compounds solubilized in bicontinuous microemulsions. Beside the kinetics of the contaminant degradation, the overall efficiency of the decontamination process is determined by the ability of the microemulsion to wet and penetrate the treated surface, as well as to extract out the contaminant.
- © AG v. Klitzing
Figure 2: a) general decontamination scheme. b) Decontamination by a microemulsion. The oil phase is the reservoir for extracted lipophilic contaminants, while the aqueous phase is the host medium for active agents. Across the amphiphilic interface of the microemulsion, the chemical decomposition to non-toxic products takes place.
Wetting properties and the microscopic structure of the microemulsions in the vicinity of solid surfaces play a crucial role in the transfer of the contaminant into the microemulsions. Therefore, we investigate the wetting properties and the near surface ordering of microemulsions (droplet and bicontinuous structures) on model and realistic surfaces with smooth and porous texture by contact angle measurements and neutron scattering techniques.
The second part of the project is directed to evaluate the extraction properties of the microemulsions in relation to different microscopic structures and their thermodynamic properties. The extraction properties are measured on porous surfaces contaminated with dyes and test molecules with similar physico-chemical properties as the chemical toxic agents. The extraction processes are monitored by means of spectroscopic and chromatographic techniques.
Salomé Vargas Ruiz
DFG: „Enzym katalysierte Reaktionen in Mikroemulsionen in der Volumenphase und an Grenzflächen“ (with: T. Hellweg (Uni Bielefeld), A. Richardt (WIS Munster))
Wellert, S., Karg, M., Imhof, H., Steppin, A., Altmann, H.-J., Dolle, M., Richardt, A., Tiersch, B., Koetz, J., Lapp, A., & Hellweg, T. ‘Structure of biodiesel based bicontinuous microemulsions for environmentally compatible decontamination: A small angle neutron scattering and freeze fracture electron microscopy study ’ J. Colloid Interf. Sci., 325, 250-258 , 2008.
Wellert, S., Tiersch, B., Koetz, J. Richardt, A., Lapp, A., Gäb, J. Holderer, O., Blum, M.-M., Schulreich, C., Stehle, R.,& Hellweg, T.‘ The DFPase from loligo vulgaris in sugar surfactant based bicontinuous microemulsions: Structure, dynamics and enzyme activity’ Europ. Biophys. J. , 40, 761-774, 2011