端基附壁高分子模型链的塌缩转变

COLLAPSE TRANSITION OF A MODEL POLYMER CHAIN TERMINALLY ATTACHED TO A SURFACE

借MonteCarlo和模拟退火方法研究了端基附壁高分子尾形链在不同温度下的形态变化 ,链的模型采用有最近邻相互吸引作用的自避行走 .计算机实验结果表明 ,对于端基附壁的高分子尾形链 ,与自由链一样 ,当温度逐渐降低时高分子链会发生从松散的无规线团到紧密球体的塌缩转变 .计算机模拟得到了端基附壁链的均方末端距及其分量 ,均方回转半径及分布随温度的变化 .由于刚性壁的影响 ,使得有限链长的高分子尾形链与自由链相比 ,其表示链尺寸 温度关系的曲线要稍低 .模拟还发现 ,在高温时壁对链形状的影响比较大 ,壁垂直方向上尺寸明显大于平行方向的尺寸 ,后者接近于自由链的尺寸分量 .然而 ,低于θ温度时 ,尤其是完全塌缩之后 ,壁对链形状的影响已经很小 .

The conformational variation of a polymer chain terminally attached to a surface at different temperatures was studied by using Monte Carlo and simulated annealing methods. The model polymer chain was a self-avoiding walk with non-bonded nearest-neighbor interactions on a simple cubic lattice. It was shown in results of computer simulations that in dilute solutions the tail chain,like the free chain,undergoes the phase transition from a loose coil to a compact globule when the temperature decreases. The,mean square end-to-end distances and their components, as well as the mean square radius of gyration and their distributions were calculated at different temperatures. Due to the existence of the surface, the curves expressing the chain size Versus temperature for the tail chain were slightly lower than those for the free chain. It was also found that the effect of the surface on the shape of the polymer chain was obvious at high temperature,and the perpendicular component of mean square end-to-end distance was significantly larger than the parallel component. However, below the theta temperature, especially after the full collapse of the polymer chain,the effect on the surface on the chain shape becomes small.