Dresden 2009 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 24: Colloids

CPP 24.2: Vortrag

Mittwoch, 25. März 2009, 14:15–14:30, ZEU 160

Testing geometrical aspects in the particle insertion free energy and depletion interaction between colloids — Martin Oettel, Vitalie Boţan, and •Florian Pesth — University of Mainz, Institute of Physics / KOMET 331, Germany

Morphological measures appear to be a useful tool to calculate the insertion free energies of particles in a solution, which is otherwise a difficult task to calculate in the case of large, irregularly shaped objects. A morphological theorem introduced by Mecke et al. states [1], that if some physical restrictions are imposed on the solute, the insertion free energy depends on only four geometric quantities. The corresponding coefficients can be obtained for the same type of particle but with a more regular shape (spheres, cylinders...) thus simplifying the calculation of the insertion energy. Dumbbell shaped objects are the first non trivial objects for studying the validity of the theorem. The dumbbell insertion free energy is also related to the depletion interaction between two hard spheres or a sphere and a wall immersed in a solvent. For such systems, it has been shown recently that standard techniques such as bulk integral equations and the Derjaguin approximation fail to describe the depletion interaction [2,3]. The morphometric approach is a natural extension of the Derjaguin approximation, is superior to it for intermediate size ratios between solute and solvent particles and compares well to explicit DFT results.

[1] P.-M. König, R. Roth, and K. R. Mecke, PRL 93, 160601 (2004) [2] M. Oettel, PRE 69, 041404 (2004) [3] A. R. Herring and J. R. Henderson, PRL 97, 148302 (2006)