Time Evolution of Domain Structure in First-Order Transition

一阶跃迁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区域。研究了聚合物晶体生长过程中畴的时间演化规律。等规聚丙烯玻璃在加热过程中依次形成选择性相和单斜相。电镜观察发现该晶体为直径约几十纳米的球形结核。在小角度x射线散射中，随着加热过程的增加，散射强度增大，最大强度的散射角减小；该域的增长得到了证实。结构域的边界是光滑的还是粗糙的是结构域生长机制中的一个重要问题。我们在覆盖Porod区域的大范围散射角范围内进行了小角度的x射线散射。聚丙烯的球状结构具有分形特征。此外，发现折叠链晶体和延伸链晶体具有分形表面。分形的概念给聚合物晶体生长理论带来了新的启示。我们还对过冷熔体中形成的球晶结构进行了光散射。结果表明，在数nm尺度上，球晶呈单轴向径向发育的球形。因此我们可以应用Avrami方程和Sekimoto理论。研究了聚苯乙烯在高过冷溶液中的结晶过程。基于粗糙表面生长理论，分析了晶化速率与层状晶体厚度的分子量依赖性。

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.