The research group Soft Matter at Interfaces is located in building S2|04 on Campus Stadtmitte.
For solid interface characterisation we use a variety of methods, such as scanning force microscopy, ellipsometry and QCM. Liquid interfaces and thin liquid films are investigated using e.g. thin film pressure balance technique, AFM and tensiometric methods.
We operate specialized laboratories providing scanning forces techniques for surface imaging and force measurements in different environments and the characterization of foams and thin liquid films.
Atomic Force Microscope (AFM) is a type of scanning probe microscopy with a high three dimensional resolution in the order of nanometres. The technique can be used in vacuum, gaseous or liquid environments and temperature can be controlled if a control unit exists. It is one of the most widely used instruments to study the interactions between two surfaces and for surface imaging in nanoscale. In principle, it can measure every surface with a force measurement range of 10-12 to 10-4 N and a lateral resolution up to 10-12 m .
The central unit of an AFM is a flexible cantilever with a probe at its end. In the scanning probe AFM, the probe is a sharp tip with a radius of curvature around 5 – 50 nm. Force measurements are mostly performed with a micron scale spherical colloidal probe attached on the cantilever . The flexible cantilever is bent depending on the interactions between the probe and the surface. The principle of the AFM exactly lies behind monitoring this bending. It is done by collecting the deflection of a laser beam reflected from the top of the cantilever.
Our lab specialises both on force measurements and scanning in air and liquid medium. We operate two Asylum Research MFP3Ds (one with a coupled fluorescence microscope), an Asylum Research Cypher and a JPK NanoWizard II.
Light scattering laboratory
The light scattering instrument consists of an ALV-goniometer setup with a Nd:YAG laser (l = 532 nm; 70 mW) and a Argon laser (l = 458 nm, 488 nm, 514 nm; tunable laser power) as switchable light sources.
The setup can be used for dynamic and static light scattering in an angle range at each angle between 30° and 110°. According to the used type of light scattering, information about particle shapes and sizes, polydispersity, the interaction between colloidal particles and the molecular weight can be achieved. In the field of polymer synthesis and microemulsions light scattering is an important method to characterize the samples. Thus, the diameter of microemulsion as well as the diameter and molecular weight of spherical shaped polymer particles can be measured.
- Berne, B.J. Pecora R., Dynamic light scattering, Dover Publication, 2000, Toronto
- Pusey, P. N. Dynamic Light Scattering, in: Neutrons, X-rays and Light: Scattering Methods Applied to Soft Condensed Matter, eds. P. Lindner, T. Zemb, Elsevier, 2002
- Glatter, O. Static Light Scattering of large Systems, in: Neutrons, X-rays and Light: Scattering Methods Applied to Soft Condensed Matter, eds. P. Lindner, T. Zemb, Elsevier, 2002
Foam films laboratory
The stability and the interactions between film surfaces can be determined in a so-called thin film pressure balance (TFPB). Both, equilibrium measurements of a disjoining pressure isotherm (disjoining pressure vs. film thickness) and dynamic film thinning experiments (film thickness vs. time) can be measured by this method. The disjoining pressure isotherms give information about the forces acting between the approaching interfaces while the dynamic measurements permit inference on kinetic parameters: thinning velocity, elasticity and stability. Usually, this apparatus is used for disjoining pressure measurements at free-standing foam films (air/liquid/air) and wetting films (air/liquid/solid) .
The disjoining pressure isotherms can be measured with the popular porous plate technique . In this case the film holder consists of a porous glass disc which is connected to a glass tube in such away that the surfactant solution is free to move. The film is formed in a small hole of diameter 1 – 2 mm drilled through the disc. The film holder is placed in a chamber where a constant gas pressure can be adjusted. The controlled variation of the applied external pressure allows a wide-range adjustment of the film thickness. The films thickness is measured interferometrically by using white light incident normal to the flat portion of the film. The film is monitored with video microscopy through a quartz window in the top of the cell.
In our group, thin films of mixtures of oppositely charged polyelectrolytes / surfactants and catanionic surfactant systems as well as the effect of electrolytes on foam and wetting films are investigated.
Physical chemistry labs
Our laboratories are fully equipped and used for hydro- and microgel synthesis and surface and interface preparation and characterisation. Additionally, tensiometric measurements and surface preparations and modifications can be performed under clean room conditions.
Synthesis & Coating
Emulsion polymerization (polymer microgels)
Atom transfer radical polymerization (polymer brushes)
Coating of solid substrates:
Spin coater (particle and polymer deposition)
Dip robot (polyelectrolyte multilayers)
Characterization of thin films & surfaces:Ellipsometry:
Quartz crystal microbalance (QCM-D)
Scanning electron microscopy (SEM)
Fluorescence recovery after photobleaching (FRAP)
Transmission electron microscopy (TEM)