Melting of Colloidal Crystals

POSTER

Abstract

We experimentally studied the melting and freezing behaviors of colloidal crystals composed of diameter tunable poly-N-isopropylacrylamide (NIPA or pNIPAM) microgel spheres by bright-field and confocal video microscopies. The melting behaviors of three-dimensional (3D), two-dimensional (2D) and multilayer thin films of both single crystals and polycrystals were systematically studied with single-particle dynamics. Thick films ($>$4 layers) melt heterogeneously, while thin films ($<$5 layers) melt homogeneously even in polycrystals. A novel heterogeneous melting at dislocation is discovered in 5- to 12-layer films. The equilibrium phase behaviors are different in three thickness regimes: thick films have a liquid-solid coexistence regime which decreases with the film thickness and vanishes at 4 layers, thin films melt into the liquid phase in one step, while monolayers melt in two steps with an intermediate hexatic phase. These results provide new challenges in theory.

*GRF grants 601208 and 601911

Authors

  • Yi Peng

    • Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
    • Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong

  • Ziren Wang

    • Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
    • Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong

  • Ahmed Alsayed

    • Complex Assemblies of Soft Matter, CNRS/UPENN/Rhodia UMI 3254, Bristol, Pennslyvania 19007, USA

  • Arjun Yodh

    • Department of Physics and Astronomy, University of Pennsylvania
    • Department of Physics \& Astronomy, University of Pennsylvania
    • University of Pennsylvania
    • Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, Pennsylvania 19104, USA

  • Yilong Han

    • Hong Kong University of Science and Technology
    • Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
    • Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong