The research interests of this area include the forces stabilizing foam films, forces between solid colloid particles, oscillatory structural forces, and wetting and transport phenomena at the nanoscale.

Research topics

Picture: AG von Klitzing

Foam Films

Foam films are thin liquid films separating air bubbles in a macroscopic foam. They are considered as building blocks of the foam. Our research interests are the forces stabilizing foam films described as disjoining pressure inside the foam film.

The main method to investigate foam films is the Thin Film Pressure Balance for measuring the disjoining pressure isotherms and optical observation of foam films. However, also surface-sensitive methods are used such as tensiometry (dynamic/static) and neutron scattering to study a single air/water interface. Surfactants, mixtures of polyelectrolytes and surfactants as well as proteins are investigated. We are interested in synergistic effects, the impact of additives (different polyelectrolytes, salt) and ion-specific effects.

Contact person:

Larissa Braun
Kevin Gräff

Selected publications:

  • Martin Uhlig, Oliver Löhmann, Salomé Vargas Ruiz, Imre Varga, Regine von Klitzing and Richard A. Campbell, New structural approach to rationalize the foam film stability of oppositely charged polyelectrolyte/surfactant mixtures, Chem. Commun., 2020, 56, 952-955.
  • Martin Uhlig, Reinhard Miller and Regine von Klitzing, Surface adsorption of sulfonated poly(phenylene sulfone)/C14TAB mixtures and its correlation with foam film stability, Phys. Chem. Chem. Phys., 2016, 18, 18414-18423.
  • Heiko Fauser, Regine von Klitzing and Richard A. Campbell, Surface Adsorption of Oppositely Charged C14TAB-PAMPS Mixtures at the Air/Water Interface and the Impact on Foam Film Stability, J. Phys. Chem. B 2015, 119, 1, 348-358.
Picture: AG von Klitzing

Forces between (cement) particles

Forces between solid colloidal particles across liquid media are of interest in fundamental science as well as in applications, such as the fabrication of cement pastes. These forces are typically described as superposition of two major contributions – the van der Waals (dispersion) and diffuse double layer (electrostatic) interactions – within the so-called DLVO theory.

We map these forces using colloidal probe atomic force microscopy (CP-AFM). In this setup, a colloidal particle is glued to a cantilever which is then used as probe for force measurements. The second surface is a flat substrate or another colloidal particle. Interaction forces are investigated at various pH, ion concentrations, concentration of polymeric additives and surfaces.

The precise knowledge of the inter-particle forces can be compared to macroscopic physical properties, such as in the rheology of cement pastes. We aim for a better understanding of these complex systems with respect to the influence of polymer additives as well as variation in pH and added salt on the particle interaction.

Contact person:

Simon Becker

Picture: AG von Klitzing

Oscillatory structural forces

Interactions between two (solid) surfaces across a liquid medium are of fundamental interest in colloid and interface science. These interactions are typically described within the so called DLVO-theory.

This theory models the liquid medium between the surfaces as continuous medium and therefore fails, once this assumption ceases to be valid. Interactions across complex fluids, such as dispersions containing nanoparticles or surfactant micelles, show interesting behaviour. The interaction force between two surfaces across these complex media can oscillate between attractive and repulsive in dependence of surface separation. These forces are caused by the liquid’s nano-structuring and are therefore often called oscillatory structural forces.

In our labs, we measure this type of forces directly by using colloidal-probe atomic force microscopy (CP-AFM) along with various supplementary measurements for the characterisation of the liquid’s properties and structure.

Contact person:

Thomas Tilger

Selected publications:

  • Michael Ludwig, and Regine von Klitzing, Recent progress in measurements of oscillatory forces and liquid properties under confinement, Current Opinion in Colloid and Interface Science, 2020, https://doi:10.1016/j.cocis.2020.02.002
  • Yan Zeng, Sebastian Schön, and Regine von Klitzing, Silica nanoparticle suspensions under confinement of thin liquid films, Journal of Colloid and Interface Science, 2015, 449, 522-529, https://doi:10.1016/j.jcis.2015.02.019
Picture: AG von Klitzing

Wetting and transport phenomena

Wetting phenomena are described on the macroscopic scale by the Young equation. A high resolution of the TPCL on a nanometer scale is required for a deeper understanding of the phenomena.

Wetting phenomena are described on the macroscopic scale by the Young equation. Close to the three-phase contact line (TPCL), the geometry dramatically changes and the interface deforms at small length scales. Another important problem are moving contact lines that are out of equilibrium considered down to molecular scales. In all these examples a high resolution of the TPCL on a nanometer scale is required for a deeper understanding of the phenomena.

The aim of our research is the understanding and control of the wetting and imbibition of mesoporous thin films on a nanoscale. Therefore, we study the TPCL at nanometer resolution. For this, we use AFM for scanning the three-phase contact line with a resolution in the order of 10-30 nm. Additionally, the surface tension of a droplet is measured with a nano Wilhelmy balance. These results are compared to outcomes from optical measurements on the macroscopic scale.

Contact person:

Mohammad Ali Hormoz

Selected publications:

  • Lüderitz, L. A. C., Klitzing, R. von: Scanning of silicon wafers in contact with aqueous CTAB solutions below the CMC. Langmuir 28 (7), 3360–3368,, 2012.
  • Hänni‐Ciunel, K., Findenegg, G. H., Klitzing, R. von: Water contact angle on polyelectrolyte‐coated surfaces: Effects of film swelling and droplet evaporation. Soft Materials 5 (2-3), 61–73,, 2007.
  • Löhmann, O., Zerball, M., Klitzing, R. von: Water uptake of polyelectrolyte multilayers including water condensation in voids. Langmuir 34 (38), 11518–11525,, 2018.