Drude-type conductivity of charged sphere colloidal crystals: density and temperature dependence.
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.
Medebach
Martin
M
Institut fur Physik, Johannes Gutenberg-Universität Mainz, Germany.
Jordán
Raquel Chuliá
RC
Reiber
Holger
H
Schöpe
Hans-Joachim
HJ
Biehl
Ralf
R
Evers
Martin
M
Hessinger
Dirk
D
Olah
Julianna
J
Palberg
Thomas
T
Schönberger
Ernest
E
Wette
Patrick
P