两平行嵌段共聚物刷自组装的Monte Carlo模拟

Monte Carlo simulation of self-assembly of the parallel diblock copolymer brush

本文运用蒙特卡洛模拟方法研究了嫁接有嵌段共聚物的两表面接近时的共聚物刷的自组装结构.对于这样一个聚合物刷体系,其体系相互作用能包括键连接部分的键能和非键连接部分的非键能,其中的键能用弹性能来表示,非键能是通过粒子表象到场表象转化的密度场来描述.对于聚合物刷体系组分之间的相互作用势,用ζ来表示,ζ<0表示两组分相吸引,ζ>0表示两组分相排斥.然后运用蒙特卡洛模拟方法对聚合物刷体系进行计算模拟.模拟结果表明:当AB两嵌段聚合物中不同组分相排斥时,则不同组分会发生相分离;当AB两嵌段聚合物中不同组分相排斥以及相同组分相吸引时,则不同组分会发生相分离,相同组分会相融合;当各组分的相互作用不变时,两平行聚合物刷的自组装随着相隔距离的增宽而相对独立进行.除此之外,还对体系势能的变化进行计算和分析,从模拟结果可以看出,随着蒙特卡洛模拟步数的进行其体系能在逐步减少,最终达到最小值,即体系将达到稳定态.同时体系体系能随着相同组分吸引作用的增强,其达到平衡态时的体系势能越低.

By using Monte Carlo simulations, we have studied the self-assembling structures of AB diblock copolyrner chains grafted on two parallel plates. The polymer chain is described by bead spring model which accounts for the boned in teractions. The non-bonded interactions between segments are expressed in terms of densities as in the field theory of polymers. In our model, we introduce parameters, ~, representing the affinity between segments, and I^p the strength of excluded volume interaction. These are two crucial quantities in determining the selLassembling morphologies of the confined dibloek copolymer brushes. We found that if the A and B segments are repulsive（~0）to each other, the brushes would separate into A and B phases with the B segments（free end）concentrating in the middle of two plates. If there is strong affinity between A segments（B segments）, the A（B）phase would collapse into clusters. With the increase of the space between two plates, the connection between brushes becomes less and less and eventually separate into two independent ones. Along with the Monte Carlo steps~ the potential energy deceases gradually and approaches a plateau at the steady state. The equilibrium structure of the system is mostly determined by the minimization of the potential energy.