半刚性高分子链塌缩相变的蒙特卡洛模拟

THE MONTE CARLO SIMULATION OF THE COLLAPSE TRANSITION OF A SEMI-STIFF POLYMER CHAIN

本文主要研究半刚性高分子链在不同温度下的形态变化,特别是在低温下的塌缩相变。我们对半刚性高分子链在三维简立方点阵上进行蒙特卡洛数值模拟。计算模型中考虑了链段间的排斥势、近邻间的吸引势和局域刚性势。链的刚性程度由刚性势与吸引势的比值确定。计算证明在温度逐步下降时,柔性链的形态由高温下的无规线团逐渐收缩为低温下的无规紧缩线团;但刚性程度较高的链则首先扩展,然后再收缩为具有一定有序度的紧缩态。同时我们也证明半刚性高分子链的塌缩相变是与柔性链的形态转变相同,它们的热力学行为都符合二级相变的特征。

The configurations and the collapsed polymer state of a semi-stiff chain under various temperatures, especially below the theta point ,are presented in this paper. The Monte Carlo method is used to simulation the behavior of a semi-stiff polymer chain in simple cubic lattice. In our model the inter-segmental interactions included the hard core volume effect, longer ranged attractive part and the local stiffness potential. The stiffness of a chain is determined by the ratio of stiffness potential and attractive effect. Our results have been obtained showing a shrinkage of the coil dimension of a polymer chain with decrease temperature. But there has some differences between a flexible chain and a semi-stiff polymer chain. At first the soil demintion of a semi-stiff chain is expanded due stiffness potential, then it shrinkage with decrease temperature. From the behaviou of the specific heat we concluded that the collapsed transitions of a polymer chain is a second-order phase transitions.