Fluid structure in colloid-polymer mixtures: the competition between electrostatics and depletion

Conference item

We studied the structure of a colloid-polymer mixture, in the one-phase region, as a function of polymer concentration. Using confocal microscopy, and Fourier transformation of the image data, we accessed the system in real and reciprocal space simultaneously, at the single particle level. We found no change in the colloidal fluid structure as a function of polymer concentration. The fluid phase persisted to higher concentrations of polymer than expected, before an abrupt gelation transition. Furthermore, we found a dramatic change in the local structure around each particle at the onset of gelation. We attribute these phenomena to a screened electrostatic repulsion between the colloids, which, although weak, suppressed the depletion attraction due to the polymer. The repulsive and attractive interactions have a similar range, which results in behaviour distinct both from pure depletion and the recently observed cluster phase formed in the presence of long-ranged electrostatic repulsions. Instead, these results are qualitatively similar to the competition between van der Waals and electrostatic interactions in the Derjaguin-Landau-Verwey-Overbeek theory. We compare our experiments with Monte Carlo simulation and find agreement with a combination of the Asakura-Oosawa-Vrij and Yukawa potentials. © 2005 IOP Publishing Ltd.

Authors: Royall, C; Aarts, D; Tanaka, H

• Publication status: Published
• Host title: JOURNAL OF PHYSICS-CONDENSED MATTER
• Volume: 17
• Issue: 45
• Pages: S3401-S3408
• Publication date: 2005-11-16
• DOI: 10.1088/0953-8984/17/45/028
• EISSN: 1361-648X
• ISSN: 0953-8984