Inhalt des Dokuments
Interactions in thin liquid films
- 1. Foam films
- 2. Wetting films
- 3. Films between two solid surfaces
1. Foam films
- Transition from "common black film" to "Newton black film" as observed in a "thin film pressure balance".
- © AG v. Klitzing
Mixtures of cationic and anionic surfactants are investigated focusing on the adsorption at aqueous surfaces. Especially the synergistic effect (also due to a variation in chain length), their aggregation behavior and the effect on foam films, foam film stability and foam lifetime are of main interest. Anther project addresses ion specific effects (Hofmeister series) and the effect of polyelectrolytes as additives.
Methods to identify are mainly surface tension (dynamic/static), thin film pressure balance and neutron scattering.
Contact: Martin Uhlig
Kristen, N.; Simulescu, V.; Vuellings, A.; Laschewsky, A.; Miller, R. & von Klitzing, R. No Charge Reversal at Foam Film Surfaces after Addition of Oppositely Charged Polyelectrolytes? J. Phys. Chem. B, 2009, 113, 7986-7990
Kristen, N.; Vuellings, A.; Laschewsky, A.; Miller, R. & von Klitzing, R. Foam Films from Oppositely Charged Polyelectolyte/Surfactant Mixtures: Effect of Polyelectrolyte and Surfactant Hydrophobicity on Film Stability. Langmuir, 2010, 26, 9321-9327
Schelero, N.; Hedicke, G.; Linse, P. & Klitzing, R. v. Effects of Counterions and Co-ions on Foam Films Stabilized by Anionic Dodecyl Sulfate. J. Phys. Chem. B, 2010, 114, 15523-15529
Kristen-Hochrein, N.; Laschewsky, A.; Miller, R. & von Klitzing, R. Stability of Foam Films of Oppositely Charged Polyelectrolyte/Surfactant Mixtures: Effect of Isoelectric Point. J. Phys. Chem. B, 2011, 115, 14475-14483
Kristen-Hochrein, N.; Schelero, N. & von Klitzing, R. Effects of oppositely charged surfactants on the stability of foam films. Colloids Surf., A, 2011, 382, 165-173
Schelero, N. & von Klitzing, R. Correlation between specific ion adsorption at the air/water interface and long-range interactions in colloidal systems. Soft Matter, 2011, 7, 2936-2942
2. Wetting films
- © AG v. Klitzing
During flotation solid particles are attached to air bubbles. In order to adsorb at the air bubble the particle is hydrophobized by the adsorption of a suitable surfactant (collector). At the same time the collector adsorbs at the air/ solution interface. Therefore, it affects both lifetime of the thin liquid film and the contact line around the particle. Up to now the correlation between the properties of the collector and its effect on the floatation mechanism are not fully understood and the choice of the collector is more or less empirical. The main problems deal with the stability of wetting films related to the adsorption of surfactant and/ or amphiphilic polymers at the solid/ liquid and air/ liquid interface.
To get a better understanding of the correlation between the simultaneous adsorption of surface active compound at a solid and a fluid interface and the stability of a wetting film formed between these two interfaces, planar wetting films as a suitable model system are studied by TFPB, ellipsometry and tensiometric methods.
Contact: Adrian Carl
Haenni-Ciunel, K.; Schelero, N. & von Klitzing, R. Negative charges at the air/water interface and their consequences for aqueous wetting films containing surfactants. Faraday Discuss., 2009, 141, 41-53
3. Films between two solid surfaces
- © AG v. Klitzing
The origin of the
oscillatory force is due to the entropic excluded volume effect in
confined thin films. The confinement induces a layered ordering of
colloidal particles or polyelectrolyte chains in the vicinity of the
confining surfaces. Therefore, studying the oscillatory force is a
direct way to understand the interaction between colloidal particles
or polyelectrolyte chains and control the stability and other
properties of the system.
We perform force measurements by using CP-AFM, in which the colloidal probe on the cantilever and the subtract act as the confining surfaces. The characteristic lengths obtained from the oscillatory force in the confined thin film are in good agreement with those obtained from the corresponding free volume (bulk) case using SAXS.
Contact: Sebastian Schön, Martin Uhlig
Zeng, Y. & von Klitzing, R. Structuring of colloidal suspensions confined between a silica microsphere and an air bubble. Soft Matter, 2011, 7, 5329-5338
Üzüm, C.; Christau, S. & von Klitzing, R. Structuring of Polyelectrolyte (NaPSS) Solutions in Bulk and under Confinement as a Function of Concentration and Molecular Weight. Macromolecules, 2011, 44, 7782-7791
Üzüm, C.; Makuska, R. & von Klitzing, R. Effect of molecular architecture on the polyelectrolyte structuring under confinement. Macromolecules, 2012, 45, 3168-3176