聚乙烯型尾形链构象统计的Monte Carlo研究

以聚乙烯型尾形链为例 ,根据链的实际键长、键角和Θ条件下每一链段处于不同旋转异构态的条件概率 ,用MonteCarlo模拟方法生成样本链分子 ,计算了尾形链的均方末端矩及其分量、构象数 ,并与完全计算法及理论推导值作了比较 ,讨论了尾形链构象数和沿边界方向及法线方向均方末端矩分量随链段数n及键角Φ的变化 .

MONTE CARLO STUDY ON CONFORMATIONAL STATISTICS FOR POLYETHYLENE TAIL CHAIN

The sample chains of polyethylene were set up by Monte Carlo simulation according to the real bond length and bond angle of PE and the conditional probabilities of a certain segment staying in one or another rotational isomeric state under θ conditions. The conformational number, the mean square end-to-end distance and its components of tail chains were calculated and compared with those from exact enumeration and theoretical deduction. The results indicated that:1) the method of Monte Carlo simulation is more accurate and converges much faster, 2) the ratio of 〈R\+2∥〉/〈R\+2-⊥〉 approaches 1/2 when the number of segments is large. It is in accordance with the theoretical deduction of half-space lattice model. The variation of conformational numbers and components of mean square end-to-end distance with number of chain segments and bond angle was also discussed. With the increase of bond angle, the number of conformation also increases, but the ratio of 〈R\+2\-\-\-∥〉/〈R\+2-⊥〉 does not change much.