Time Evolution of Domain Structure in First-Order Transition

一阶相变伴随着序参数的不连续变化，例如，密度在两相交界处发生突变。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微区随时间的演化规律。等规聚丙烯玻璃在加热过程中依次形成斜晶相和单斜相。电子显微镜观察表明，该微晶为直径几十nm的球形结节。在小角X射线散射中，随着加热过程的进行，散射强度增大，强度最大处的散射角减小，证实了微区的长大。微区边界是光滑还是粗糙，是微区生长机制中的一个重要问题。我们在覆盖波罗德区的大范围散射角范围内进行了小角X射线散射。发现结节状聚丙烯具有分形性。此外，还发现折叠链晶体和延伸链晶体具有分形面。分形学的概念为聚合物晶体生长理论提供了新的思路。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，在几个纳米尺度上，球晶是单轴微晶呈放射状发展的球体。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行为，并基于粗糙面生长理论分析了结晶速率和片晶厚度对分子量的依赖关系。

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.