Regensburg 2010 – wissenschaftliches Programm
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BP: Fachverband Biologische Physik
BP 28: Focus: Charge Effects in Soft and Biological Matter II (joint CPP, BP, ST)
BP 28.1: Hauptvortrag
Donnerstag, 25. März 2010, 14:00–14:30, H37
Electrostatic effects on depletion forces — •Roberto Piazza1, Stefano Buzzaccaro1, Jader Colombo2, and Alberto Parola2 — 1Dipartimento CMIC, Politecnico di Milano, Milano (Italy) — 2Dipartimento di Fisica e Matematica, Università dell'Insubria, Como (Italy)
Short-ranged depletion forces give rise to a phase behavior which is totally foreign to simple molecular systems, allowing to investigate new scenarios of noticeable interest for condensed matter physics. Yet, so far, most experimental and theoretical efforts have concentrated on depletion effects induced by an ideal agent.
Here, conversely, we focus on systems where strong electrostatic coupling is present. After reviewing some recent results we have obtained by sedimentation measurements on a model system of ``sticky'' hard-spheres, where depletion forces are induced by nonionic surfactants, we shall present novel results pointing out the dramatic effects that the presence of a self-interacting depletant may bring in. In particular, we shall show that electrostatic repulsive forces between the depletant yield a strong increase of depletion effects, scaling with the Debye-Hückel screening length. Conversely, competitive electrostatic forces between the colloidal particles hinder, and may even totally quench depletion-induced phase separation. The observed effects are fairly well accounted for by a theoretical analysis, based on liquid-state theory, of the structural properties of the two-components (colloids + surfactant micelles) fluid.