活性三嵌段共聚物的凝胶化转变

Gel transition of active triblock copolymers

活性物质的自推进特征引发了许多非平衡自组织现象,而聚合物链的构象自由度可以使链产生独特的平衡自组装行为,这激发了活性物质与聚合物物理的交叉研究.本文通过分子动力学模拟,研究了自驱动活性对ABA型三嵌段共聚物凝胶化转变的调控.研究结果表明活性嵌段共聚物凝胶的塌缩源于自驱动活性引起的网络链运动,活性越大则凝胶网络越容易产生大直径空洞.在凝胶网络的拓扑缺陷方面,当A嵌段之间吸引强度较大时,环链比例随活性力增强而增大,吸引强度较小时情况则相反.交联点的分支数随活性的变化除了受到吸引强度的影响,还与链刚性有关.在动力学方面,活性聚合物的定向运动会引发稳定聚合物凝胶整体的反常扩散.本文的研究有助于增进对活性聚合物集体行为的认识,为高分子活性材料的设计和应用提供了新的思路.

The self-propulsion of active matter leads to many non-equilibrium self-organization phenomena,and the conformational freedom of polymer chains can produce unique equilibrium self-assembly behaviors,which stimulates cross-disciplinary research between active matter and polymer physics.In this work,we use molecular dynamics simulations to investigate the modulation of self-propulsion activity on the gel transition of ABA triblock copolymers.The research results indicate that under different active forces and attractive strengths,the gel states formed by ABA copolymers can be divided into three types:stable polymer gels with stable percolation paths and uniform spatial distribution,dynamic polymer gels with constantly changing percolation path and strand conformation,and collapsed polymer gels aggregating into large percolating clusters.The spatial uniformity of active gels is related not only to the concentration fluctuation during the formation of the network,but also to the inconsistent movement of the network chains caused by the activity,which is manifested in the rotation of crosslinking points in the flexible system and the directional movement of the bundles along their contour directions in the semi-flexible and rigid systems.In terms of topological conformation of polymer networks,when the attractive strength between A blocks is strong,the proportion of loop increases with the active force increasing.When attractive strength is weak,inter-and intra-chain binding are unstable,and the conformation is easily changed by the activity drive,noise and other chain collisions,so the proportion of loop decreases with the active force increasing.The branching number of crosslinking points varies with active force,which is not only affected by the attraction strength,but also related to the rigidity of the network chain.Generally,the branch number of crosslinking points in semi-flexible networks is larger than that in flexible and rigid networks.In addition,the directional motion of active polymers induces anomalous diffusion in stable polymer gels.This study contributes to the understanding of the collective behavior of active polymers and serves as a guide for designing and implementing active polymeric materials.