期刊
PHYSICAL REVIEW E
卷 83, 期 1, 页码 -出版社
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevE.83.011404
关键词
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资金
- RGC [601208]
- NSF [DMR-080488]
- MRSEC [DMR-0520020]
- NASA [NAG-2939]
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 ofmelting processes in polycrystalline films thicker than 12 layers. The heterogeneous melting from dislocations is found to coexist with grain-boundary melting in films bewteen 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.
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