Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455-0132, USA.
Department of Chemistry, University of Minnesota, Minneapolis, MN 55455-0431, USA.
Science. 2017 May 5;356(6337):520-523. doi: 10.1126/science.aam7212.
Small-angle x-ray scattering experiments conducted with compositionally asymmetric low molar mass poly(isoprene)--poly(lactide) diblock copolymers reveal an extraordinary thermal history dependence. The development of distinct periodic crystalline or aperiodic quasicrystalline states depends on how specimens are cooled from the disordered state to temperatures below the order-disorder transition temperature. Whereas direct cooling leads to the formation of documented morphologies, rapidly quenched samples that are then heated from low temperature form the hexagonal C14 and cubic C15 Laves phases commonly found in metal alloys. Self-consistent mean-field theory calculations show that these, and other associated Frank-Kasper phases, have nearly degenerate free energies, suggesting that processing history drives the material into long-lived metastable states defined by self-assembled particles with discrete populations of volumes and polyhedral shapes.
小角 X 射线散射实验表明，组成不对称的低摩尔质量聚异戊二烯-聚（乳酸）嵌段共聚物具有特殊的热历史依赖性。从无序状态冷却到低于有序-无序转变温度的温度时，独特的周期性晶体或非周期性准晶态的发展取决于样品的冷却方式。直接冷却会导致形成已记录的形态，而从低温快速淬火的样品在加热时会形成通常在金属合金中发现的六方 C14 和立方 C15 拉弗斯相。自洽平均场理论计算表明，这些相以及其他相关的弗兰克-卡珀相具有几乎简并的自由能，这表明加工历史将材料驱动到由具有离散体积和多面体形状的粒子自组装而成的长寿命亚稳状态。
