Issue
EPL
Volume 87, Number 3, August 2009
Article Number 34001
Number of page(s) 6
Section Electromagnetism, Optics, Acoustics, Heat Transfer, Classical Mechanics, and Fluid Dynamics
DOI http://dx.doi.org/10.1209/0295-5075/87/34001
Published online 26 August 2009
EPL, 87 (2009) 34001
DOI: 10.1209/0295-5075/87/34001

Buckling and layering transitions in confined colloids

D. K. Satapathy1, K. Nygård1, O. Bunk1, K. Jefimovs2, E. Perret1, A. Diaz3, F. Pfeiffer1, 4, C. David1 and J. F. van der Veen1, 5

1   Research Department of Synchrotron Radiation and Nanotechnology, Paul Scherrer Institut CH-5232, Villigen PSI, Switzerland
2   EMPA - Überlandstrasse 129, CH-8600 Dübendorf, Switzerland
3   European Synchrotron Radiation Facility - B.P. 220, F-38042 Grenoble, Cedex 9, France, EU
4   École Polytechnique Fédérale de Lausanne - CH-1015 Lausanne, Switzerland
5   ETH Zürich - CH-8093 Zürich, Switzerland

dillip.satapathy@psi.ch

received 9 April 2009; accepted in final form 20 July 2009; published August 2009
published online 26 August 2009

Abstract
We report layering transitions within a charged silica colloidal dispersion confined by two opposite like-charged dielectric walls. The ensemble-averaged concentration profiles of the colloids (radius 60$\pm$2 nm) along the confinement direction have been determined using synchrotron X-ray diffraction from microfluidic arrays of channels of different widths. For small channel widths up to a critical value of 300 nm, the channel can accommodate just one layer of colloids which is stabilized against buckling by the confining charged walls. For channel widths larger than this critical value, a buckling of the single layer is observed. These phenomena are explained using a theoretical analysis of buckling instabilities due to Chou and Nelson, and a value for the charge density on the stabilizing charged walls is derived. At still larger channel widths a sequence of complex layering transitions is observed which involve the splitting and merging of individual layers.

PACS
47.57.-s - Complex fluids and colloidal systems.
61.05.C- - X-ray diffraction and scattering.
68.08.-p - Liquid-solid interfaces.

© EPLA 2009