# Regensburg 2002 – wissenschaftliches Programm

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# DY: Dynamik und Statistische Physik

## DY 46: Poster

### DY 46.19: Poster

### Donnerstag, 14. März 2002, 15:30–18:00, D

**Experimental determination of colloidal effective charges** — •Thomas Palberg, Hans Joachim Schöpe, Patrick Wette, and Martin Medebach — Universität Mainz, Inst. f. Physik, KOMET336, Staudinger Weg 7, D - 55099 Mainz

Charged colloidal spheres in aqueous suspension are known to form fluid and solid phases, if the strength and range of their mutual interaction is large enough. Their structural, elastic and diffusive properties have been measured quite comprehensively and are most often well described using a screened Coulomb potential with an effective charge Z* as only fitting parameter. On the theoretical side calculations and simulations on different levels of approximation also agree, that at large particle distances the pair interaction is of screened Coulomb type. However, concerning the value of Z* theoretical calculations and determinations from different experiments often disagree with each other. We here present a comparison of effective charges from several different experiments performed on the same set of samples. Within each experiment we find the effective charges to be independent of particle concentration. Further, for isolated particles, Z* is given by the ratio between the diameter and the Bjerrum length. For interacting particles we observe the values of Z* to differ significantly for conductivity and elasticity experiments, but with approximately constant ratios. Possible explanations are discussed.