Abstract
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.