Time Evolution of Domain Structure in First-Order Transition

一级相变伴随着序参量的不连续变化，例如，密度在两相边界处突然变化。被边界包围的区域称为域。研究了聚合物晶体生长过程中电畴随时间的演化。等规聚丙烯玻璃在升温过程中先后形成了近晶相和单斜相。电子显微镜观察表明，微晶为直径几十nm的球形结节。在小角X射线散射中，随着加热过程的进行，散射强度增加，强度最大值的散射角减小，证实了畴的生长。畴界是光滑的还是粗糙的是畴生长机制中的一个重要问题。我们进行了小角X射线散射在一个广泛的散射角覆盖Porod的区域。发现聚丙烯颗粒是分形的。此外，还发现折叠链晶体和伸展链晶体具有分形表面.分形的概念为聚合物晶体生长理论提供了新的视角。我们还进行了光散射在过冷熔体中发展的球晶结构。结果表明，在几个纳米尺度范围内，球晶为球形，单轴微晶呈放射状发育。因此，我们可以应用Avrami方程和Sekimoto理论。本文研究了聚苯乙烯在过冷溶液中的结晶行为，并基于粗糙表面生长理论分析了结晶速率和层状晶体厚度与分子量的关系。

First-order transition accompanies the discontinuous change in order parameters; for example, density changes abruptly at the boundary of two phases. The region surrounded by the boundary is called domain. The time evolution of the domain was studied on the crystal growth of polymers. The glass of isotactic polypropylene was warmed to form seectic phase and monoclinic phase successively on heating . Electron microscopy revealed that the crystallite was spherical nodule of a few tens nm in diameter. In small angle X-ray scattering , the scattered intensity increases and the scattering angle of the intensity maximum decreases on heating process; the growth of the domain was confirmed. Whether the boundary of the domains is smooth or rough is an important issue in growth mechanism of the domains. We performed small angle X-ray scattering in a wide range of scattering angle covering Porod's region. The nodular polypropylene was found to be fractal. Furthermore, the folded chain crystals and the extended chain crystalswere found to have the fractal surface. The concept of fractals has thrown a new light on the theory of crystal growth of polymers. We also performed light scattering on spherulite structure developed in supercooled melt. The result showed that in the dimension of several nm the spherulite was a sphere in which uni-axial crystallites developed radially. Therefore we can apply Avrami's equation and the theory of Sekimoto.Crystallization from highly supercooled solution was studied on polystyrene; molecular weight dependence of crystallization rate and thickness of lamellar crystals was analyzed on a theory based on rough-surface growth.