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Crystal patterns in ultrathin films of six poly(ethylene oxide) fractions with molecular weights from 25000 to 932000 g/mol were characterized within crystallization temperature range from 20 ℃ to 60 ℃.Labyrinthine,dendritic and faceted crystal patterns were observed in different temperature ranges,and then labyrinthine-to-dendritic and dendritic-tofaceted transition temperatures T L-D and T D-F were quantitatively identified.Their molecular weight dependences are T L-D(M w) = T L-D(∞) K L-D /M w,where T L-D(∞) = 38.2 ℃ and K L-D = 253000 ℃.g/mol and T D-F(M w) = T D-F(∞) K D-F /M w,where T D-F(∞) = 54.7 ℃ and K D-F = 27000 ℃.g/mol.Quasi two-dimensional blob models were proposed to provide empirical explanations of the molecular weight dependences.The labyrinthine-to-dendritic transition is attributed to a molecular diffusion process change from a local-diffusion to diffusion-limited-aggregation(DLA) and a polymer chain with M w ≈ 253000 g/mol within a blob can join crystals independently.The dendritic-to-faceted transition is attributed to a turnover of the pattern formation mechanism from DLA to crystallization control,and a polymer chain with a M w ≈ 27000 g/mol as an independent blob crosses to a depletion zone to join crystals.These molecular weight dependences reveal a macromolecular effect on the crystal pattern formation and selection of crystalline polymers.
Crystal patterns in ultrathin films of six poly (ethylene oxide) fractions with molecular weights from 25000 to 932000 g / mol were characterized by crystallization temperature range from 20 ° C. to 60 ° C. Labyrinthine, dendritic and faceted crystal patterns were observed in different temperature ranges, and then labyrinthine-to-dendritic and dendritic-tofaceted transition temperatures T LD and T DF were quantitatively identified. Their molecular weight dependences are T LD (M w) = T LD (∞) K LD / M w, where T LD ) = 38.2 ° C and K LD = 253000 ° C .g / mol and T DF (M w) = T DF (∞) K DF / M w where T DF (∞) = 54.7 ° C and K DF = / mol.Quasi two-dimensional blob models were proposed to provide an empirical explanations of the molecular weight dependences.The labyrinthine-to-dendritic transition is attributed to a molecular diffusion process change from a local-diffusion to diffusion-limited-aggregation (DLA) and a polymer chain with M w ≈ 253000 g / mol within a blob can jo in crystals independently. The dendritic-to-faceted transition is attributed to a turnover of the pattern formation mechanism from DLA to crystallization control, and a polymer chain with a Mw w≈ 27000 g / mol as an independent blob crosses to a depletion zone to join crystals.These molecular weight dependences reveal a macromolecular effect on the crystal pattern formation and selection of crystalline polymers.