Layering transitions in confined colloidal crystals: The hcp-like phase

F. Ramiro-Manzano; E. Bonet; I. Rodriguez; F. Meseguer

doi:10.1103/PhysRevE.76.050401

Research · Publication & note

Layering transitions in confined colloidal crystals: The hcp-like phase

Rapid Communication

F. Ramiro-Manzano, E. Bonet, I. Rodriguez and F. Meseguer

Phys. Rev. E Volume 76 050401(R) 2007

Abstract

This paper investigates the sequence of morphological transitions in a nearly hard sphere arrangement confined in a wedge cell. A model that shows smooth transitions between the different particle orderings for a small range of confinement is proposed. The hcp-like phase appears as a general adaptive structure in the transitions between two and six layers.

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Article access and reuse

APS author rights permit authors to use all or part of an APS-published article, including APS-prepared figures, on the author's or employer's website without charging a fee. The four complete figures below were extracted from the local PDF at 300 dpi and are reproduced without modification.

Figures

Complete Figure 1 composition from the original article PDF, with all panels, axes and units — **Figure 1.** Reflectance spectra and SEM images for the transition between two and three layers.

Complete Figure 2 composition from the original article PDF, with all panels, axes and units — **Figure 2.** Filling fraction as a function of reduced cell thickness with ordering models showing the phase evolution.

Complete Figure 3 composition from the original article PDF, with all panels, axes and units — **Figure 3.** Reflectance spectra and SEM images for the transition between three and four layers.

Complete Figure 4 composition from the original article PDF, with all panels, axes and units — **Figure 4.** SEM images of hcp-like phases with four, five and six monolayers.

Research fields

Bottom-up

Spheres confined in a wedge cell assemble into layer-dependent colloidal crystals as the plate separation changes. Between conventional triangular and square packings they form an hcp-like arrangement that continuously adapts its distortion to the available gap.

Simulations & fits

Filling-fraction calculations model buckling and hcp(100) order as limiting cases of one continuous family. This provides a geometrical pathway through the transition and predicts where each intermediate arrangement should be stable.

Characterization

Position-resolved infrared reflectance and SEM imaging follow the same thickness gradient. Spectral discontinuities locate phase boundaries, while surface and edge micrographs identify the particle stacking responsible for each optical change.

RESEARCH TOPICS

MaterialsA wedge cell forces a nearly hard-sphere colloid to accommodate a continuously changing gap with an integer number of layers. The paper identifies an hcp-like family that connects the usual buckled, rhombic and HCP(100) arrangements through smooth changes in interlayer spacing rather than abrupt replacement of one ideal lattice by another. Optical reflectance and SEM determine facet orientation, spacing and monolayer count, allowing hcp-like order up to six layers and the complete two-to-four-layer sequence to be reconstructed. The result explains how finite crystals remain commensurate with confinement without requiring discontinuous density jumps at every transition.