Confinement-induced orientational alignment of quasi-2D fluids

¹  Research Department of Synchrotron Radiation and Nanotechnology, Paul Scherrer Institut CH-5232 Villigen PSI, Switzerland
²  Institute of Solid State Research, Forschungszentrum Jülich - D-52425 Jülich, Germany, EU
³  ETH Zürich - CH-8093 Zürich, Switzerland

Corresponding author: kim.nygard@psi.ch

Received: 8 May 2009
Accepted: 3 June 2009

Abstract

We have developed a unique approach for studying the ensemble-averaged nearest-neighbor coordination of confined fluids by combining small-angle X-ray scattering and phase-retrieval–based X-ray diffraction from fluid-filled nanofluidic channel arrays. We apply the method to a charge-stabilized quasi–two-dimensional colloidal fluid (particle diameter 48 nm), focusing on the structural transition from a monolayer to a bilayer with increasing fluid film thickness. In contrast to theoretical work on the paradigmatic hard-sphere fluid, we find unambiguous experimental evidence for orientational alignment of fluids in extreme confinement.