Li Wang

Chinese Academy of Sciences, Peping, Beijing, China

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Publications (4)18.28 Total impact

  • Li Wang · Jiang Zhao · Charles C. Han
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    ABSTRACT: Phase separation of a triblock copolymer, polystyrene-b-(ethylene-co-butylene)-b-styrene (SEBS) on the thin films of a homopolymer, polystyrene (PS), was studied by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The final morphology after phase separation was found to be greatly dependent on the relation between the molecular weight of the PS block and homo-PS. Dispersed spherical and worm-like micelles of SEBS were observed when the molecular weight of homo-PS is smaller than the PS block in SEBS, while large structures with inner micro-phase separation of SEBS was found when the molecular weight of homo-PS was much higher than that of the PS block. The origin of such a change in morphology is attributed to the difference of structure and interfacial tension at the interface between the matrix homo-PS and the PS block in SEBS triblock copolymer assembly.
    Polymer 04/2008; 49(8):2153-2159. DOI:10.1016/j.polymer.2008.02.037 · 3.56 Impact Factor
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    ABSTRACT: The surface effect of thin films of PEH/PEB in order to interpret the effect of Liquid-liquid phase separation (LLPS) on the nucleation of crystallization process has been discussed. The breakdown of dynamic scaling in thin film binary liquids undergoing phase separation has already been reported. The fluctuation assisted crystallization in PEH/PEB blend films of thickness close to or less than the domain size of the spinodal decomposition was investigated by optical microscopy and scanning electron microscopy. The result show that the effect of LLPS time on nucleation rate of subsequent crystallization strongly dependent on the film thickness. The nucleation rate in thicker films decreases with LLPS time to the minus one-third power, t -1/3, which is similar to that of bulk case. The nucleation rate for the thinner films becomes insensitive to the LLPS time, t, gradually,when the increasing domain size exceeded the film thickness.
    Macromolecules 03/2008; 41(7). DOI:10.1021/ma7025379 · 5.80 Impact Factor
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    ABSTRACT: The dewetting process of an ultrathin film of a triblock copolymer, poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) was studied with an atomic force microscope. The surface morphology of the dewetting process exhibited two distinct dewetting processes of the 5.6 nm thick films: a slower dewetting for the polymer layer at the very vicinity of the substrate's surface, and a faster one for the polymer on top of this layer. The surface-induced difference in the kinetics of these two-step dewetting processes resulted in a special morphology evolution, including the absence of the dewetting rim, and a final unique network-like morphology.
    Langmuir 03/2007; 23(5):2304-7. DOI:10.1021/la063314u · 4.46 Impact Factor
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    ABSTRACT: Based on hydrogen-bonding layer-by-layer (LBL) assembly in aqueous solution, poly(vinylpyrrolidone) (PVPON) and a spherical polymer brush with a poly(methylsilsesquioxane) (PSQ) core and poly(acrylic acid) (PAA) hair chains were used to fabricate composite multilayer thin films. Hydrogen bonding as the driving force was confirmed by FT-IR spectrometry. A simple method (Filmetric F20) was introduced to determine the thickness and refractive index of the films. The film thickness was found to be a linear function of the number of bilayers. The average increase in thickness per bilayer is 28.3 nm. The film morphology was characterized with scanning electron microscopy and atomic force microscopy. The images obtained from the two instruments show a great resemblance. The films were further calcined to get an inorganic film by removing the organic components, or treated with tetrabutylammonium fluoride (TBAF) to remove the PSQ core and get an organic film. The optical properties and morphological changes induced by these treatments were also studied.
    Langmuir 02/2006; 22(1):338-43. DOI:10.1021/la051581e · 4.46 Impact Factor