Confinement-induced orientational alignment of quasi-2D fluids

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. Copyright (C) EPLA, 2009