Benetzung einzelner kolloidaler Teilchen durch adaptive Grenzflächen

• Applicant: Dr. Karlheinz Graf
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2002 to 2005
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 5365098

We intend to investigate with a new method the interaction of a solid surface with an adaptive interface, which reacts on the approach of a solid micro-particle. This can be achieved in a modified Langmuir trough, which allows for simply adjusting the molecular coverage of a monolayer of insoluble, amphiphilic molecules. We plan to measure force-distance curves (force curves) from below the monolayer by means of a modified atomic force microscope (AFM) and simultaneously observe molecular changes within the monolayer by means of fluorescence microscopy from above. To measure the force curves, we attach a microparticle to the AFM cantilever instead of the tip which has been shown to work properly in the particle interaction apparatus (PIA). There, the micro-particle measures the forces on a liquid-gas interface formed by a gas bubble sitting on a solid substrate. Thus, the influence of surfactants like SDS or DTAB on the force curves was investigated and a pronounced dependence of the acting forces on the tenside concentration has been found. The results could only be be understood when taking into account a partial but unknown adsorption of the tensides on the tip. This disadvantage can be overcome by the new method, which basically is a combination of PIA and a Langmuir trough. For differently charged lipids we expect pronounced differences in the hysteresis during an approach-retraction cycle. From the velocity dependence of the hysteresis we hope to derive the molecular interaction energy between the film and the solid surface of the micro-particle.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1052: Benetzung und Strukturbildung an Grenzflächen
• Major Instrumentation: System zur Kraftmessung, Komponenten für den Eigenbau
• Instrumentation Group: 8970 Kraftmeßgeräte (einschl. elektronischem Anzeigegerät)
• Participating Person: Dr. Michael Kappl