Thermodynamics, Kinetics and Rheology of Interfacial Layers
1. Thermodynamics of Surfactant and Protein Adsorption Layers
Thermodynamic models are developed to describe the equilibrium state of adsorption layers. The starting point is the principle of Braun-Le Chatelier. Different states of surfactant or protein molecules in an adsorption layer are assumed, controlled by the surface pressure.
Isotherms for surfactants are derived which take into consideration
- ideal and non-ideal entropy of mixing in the adsorption layer
- coexisting adsorption states of different molecular area
- aggregation in the adsorption layer
For protein adsorption layers isotherms have been derived which
- allow for different molecular surface area of an adsorbed molecule
- yield a distribution of molecular conformation
- give information on the adsorption layer thickness
For mixtures of surfactants first quantitative models have been published recently. These models give a very good description of experimental data, mainly in form of surface tension isotherms.
Main targets of research on this topic are
- experiments for selected mixed surfactant systems
- analysis of protein adsorption data at water/air and water/oil interfaces
- performance of experiments for mixed surfactant / protein systems
- understanding of parallels between adsorbed proteins and nano-particles
This work is performed in direct collaboration with the groups of Valentin B. Fainerman from Donetsk, Emmi Lucassen-Reynders from Vlaardingen, Eugene Aksenenko and Vladimir Kovalchuk from Kiev, Martin Leser from Lausanne.
Link to useful software tools for the analysis and prediction of the behaviour of adsorbed monolayers.
2. Adsorption Kinetics of Surfactants, Proteins and their Mixtures
Experimental technique has been developed and modified such that the adsorption kinetics can be studied in a wide time interval
- maximum bubble pressure method (0.0001 s to 100 s)
- drop volume method (0.5 s to 600 s)
- pendent drop technique (1 s to 100000 s)
- ellipsometry (10 s to 10000s).
Theoretical models developed recently allow to take into consideration new features obtained from the equilibrium adsorption state: orientational changes, interfacial aggregation, phase transitions. The combination of dynamic surface tensions with ellipsometry creates a new situation for a quantitative understanding of adsorption mechanisms in particular for proteins and mixed protein-surfactant systems. Moreover, the adsorption dynamics data together with the thermodynamic behaviour of the respective adsorption layers must complement with the parameters of dilational rheology.
Main targets of research on this topic are
- performance of new experiments for mixed surfactant systems
- performance of new experiments for mixed surfactant protein systems
- development of quantitative models for mixed surfactant systems
- development of new protein adsorption kinetics models
- models for adsorption of nano-particles at liquid interfaces
This work is performed in close collaboration with the groups of Valentin B. Fainerman from Donetsk, Vladimir Kovalchuk and Eugene Aksenenko from Kiev, Martin Leser from Lausanne, Libero Liggieri from Genoa and Giuseppe Loglio from Florence.
Link to useful software tools for the analysis and prediction of the behaviour of adsorbed monolayers.
3. Surface Rheology of Adsorption Layers
The work to this topic is focused on shear and dilational rheology of two-dimensional layers at liquid interfaces and on interfacial relaxation processes.
The shear rheology studies with a torsion shear rheometer are performed with
- adsorbed and spread protein layers
- adsorbed mixed protein-surfactant layers
- spread surfactant layers
- mixed protein-lipid layers (model lung surfactants)
- layers formed by nano-particles and surfactants
The studies of the dilational rheology is based on different techniques
- transient relaxations (pendent drop methods)
- oscillating barrier method (0.01 to 1 Hz)
- longitudinal wave damping (0.1 to 15 Hz)
- capillary wave damping (10 to 500 Hz)
- oscillating drop and bubble method (0.01 to 200 Hz)
Systems studied with these techniques are
- surfactant and protein adsorption layers
- mixed protein-surfactant systems
- micellar surfactant solutions
- lung surfactant dispersions
- biologically relevant liquids (blood, urine)
Main targets of research on this topic are
- performance of new experiments for mixed surfactant systems
- performance of new experiments for mixed surfactant protein systems
- development of new theoretical models for viscoelastic interfacial layers
This work is performed in close collaboration with the groups of Giuseppe Loglio from Florence, Boris Noskov from St. Petersburg, Valentin B. Fainerman from Donetsk, James Ferri from Lafayette, Libero Liggieri from Genoa, and Martin Leser from Lausanne.
4. Characterisation of Emulsion and Foam Systems
Beside the characterisation of adsorption layers at liquid interfaces also complex liquid systems, such as foams and emulsions are studied. Especially the correlation between the properties of single layers with those of liquid films and further of liquid disperse systems are in the centre of interest.
Techniques used are
- Confocal microscopy to study processes in diluted emulsions
- Foam Analyser to determine foams properties
- Liquid film balances
Systems under study are
- soluble surfactant systems
- protein layers
- mixed surfactant - protein layers
- nano-particle layers
Main targets of research on this topic are
- foam stability experiments for surfactants and mixtures
- develop a method for dilational rheology of free liquid films
- development of models to correlate emulsion and emulsion film properties with characteristic parameters of adsorption layers
- development of models to correlate film and foam properties with characteristic parameters of adsorption layers
- elaborate new models for emulsion stability
This work is performed in close collaboration with the groups of Cosima Stubenrauch from Stuttgart, Dotchi Exerowa and Khristo Kristov from Sofia, Regine von Klitzing from Berlin, Stanislaw Dukhin from New York, Natasha Mishchuk from Kiev, Annie Steinchen and Mickael Antoni from Marseille.