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Alan Denton: „Polymer Shapes: A Random Walk from Depletion to Demixing in Colloid-Polymer Mixtures”
Department of Physics, North Dakota State University, Fargo, USA

Physical properties and stability of colloidal suspensions (paints, clays, foods, pharmaceuticals) often hinge on effective interactions between colloids induced by depletion of nonadsorbing polymers from a confined space.
The strength and range of depletion-induced forces vary with polymer geometry. Conformational entropy favours a random-walk coil for a linear polymer (e.g., hydrocarbon chain) on length scales much exceeding the persistence length of the coil. Even non-self-avoiding polymer coils, however, are quite aspherical and fluctuate in size (radius of gyration) and shape. Moreover, polymer coils -- like coastlines, clouds, and galaxies -- are tenuous objects with fractal structure, the density of chain segments decaying away from the centre. Modeling polymer coils as penetrable ellipsoids with fluctuating principal radii, we apply free-volume theory and Monte Carlo simulation to explore depletion and demixing phase behaviour in colloid-polymer mixtures.