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...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-to- faceted 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/tool 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.展开更多
基金financially supported by the National Science Foundation of China(No.20874053)
文摘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-to- faceted 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/tool 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.
