title: Melting of multilayer colloidal crystals confined between two walls.
abstract: Video microscopy is employed to study the melting behaviors of multilayer colloidal crystals composed of diameter-tunable microgel spheres confined between two walls. We systematically explore film thickness effects on the melting process and on the phase behaviors of single crystal and polycrystalline films. Thick films (>4 layers) are observed to melt heterogeneously, while thin films (≤4 layers) melt homogeneously, even for polycrystalline films. Grain-boundary melting dominates other types of melting processes in polycrystalline films thicker than 12 layers. The heterogeneous melting from dislocations is found to coexist with grain-boundary melting in films between 5- and 12-layers. In dislocation melting, liquid nucleates at dislocations and forms lakelike domains embedded in the larger crystalline matrix; the "lakes" are observed to diffuse, interact, merge with each other, and eventually merge with large strips of liquid melted from grain boundaries. Thin film melting is qualitatively different: thin films homogeneously melt by generating many small defects which need not nucleate at grain boundaries or dislocations. For three- and four-layer thin films, different layers are observed to have the same melting point, but surface layers melt faster than bulk layers. Within our resolution, two- to four-layer films appear to melt in one step, while monolayers melt in two steps with an intermediate hexatic phase.
authors.affiliation: Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.
authors.forename: Y
authors.initials: Y
authors.lastname: Peng
authors.forename: Z-R
authors.initials: ZR
authors.lastname: Wang
authors.forename: A M
authors.initials: AM
authors.lastname: Alsayed
authors.forename: A G
authors.initials: AG
authors.lastname: Yodh
authors.forename: Y
authors.initials: Y
authors.lastname: Han