title: Drude-type conductivity of charged sphere colloidal crystals: density and temperature dependence.
abstract: We report on extensive measurements in the low-frequency limit of the ac conductivity of colloidal fluids and crystals formed from charged colloidal spheres suspended in de-ionized water. Temperature was varied in a range of 5 degrees C < Theta < 35 degrees C and the particle number density n between 0.2 and 25 microm(-3) for the larger, respectively, 2.75 and 210 microm(-3) for the smaller of two investigated species. At fixed Theta the conductivity increased linearly with increasing n without any significant change at the fluid-solid phase boundary. At fixed n it increased with increasing Theta and the increase was more pronounced for larger n. Lacking a rigorous electrohydrodynamic treatment for counterion-dominated systems we describe our data with a simple model relating to Drude's theory of metal conductivity. The key parameter is an effectively transported particle charge or valence Z(*). All temperature dependencies other than that of Z(*) were taken from literature. Within experimental resolution Z(*) was found to be independent of n irrespective of the suspension structure. Interestingly, Z(*) decreases with temperature in near quantitative agreement with numerical calculations.
authors.affiliation: Institut fur Physik, Johannes Gutenberg-Universität Mainz, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Medebach
authors.forename: Raquel Chuliá
authors.initials: RC
authors.lastname: Jordán
authors.forename: Holger
authors.initials: H
authors.lastname: Reiber
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Schöpe
authors.forename: Ralf
authors.initials: R
authors.lastname: Biehl
authors.forename: Martin
authors.initials: M
authors.lastname: Evers
authors.forename: Dirk
authors.initials: D
authors.lastname: Hessinger
authors.forename: Julianna
authors.initials: J
authors.lastname: Olah
authors.forename: Thomas
authors.initials: T
authors.lastname: Palberg
authors.forename: Ernest
authors.initials: E
authors.lastname: Schönberger
authors.forename: Patrick
authors.initials: P
authors.lastname: Wette