聚电解质单链在盐溶液中构象转变的并行回火蒙特卡罗研究  

A Parallel Tempering Monte-Carlo Study of Conformation Transitions of a Single Polyelectrolyte Chain in Solutions with Added Salt

作　　者：王朗[1] 王铮[1] 尹玉华[1] 蒋润[1] 李宝会[1] 

机构地区：[1]南开大学物理科学学院,天津300071

出　　处：《高分子学报》2017年第12期1984-1992,共9页Acta Polymerica Sinica

基　　金：国家自然科学基金(基金号21574071;21528401;20925414;91227121);教育部创新团队发展计划(项目号IRT1257);高等学校学科创新引智计划(项目号B16027)资助

摘　　要：采用并行回火蒙特卡罗方法,研究了聚电解质单链在盐溶液中的构象转变以及离子的凝聚行为.对不同盐浓度以及不同价态的情况,得到了链均方回转半径(<Rg2>)随Bjerrum长度lB的变化曲线.模拟结果表明,在不同浓度与价态的盐溶液中,随着lB的增加,链先伸展,然后收缩,最终形成塌缩态.链尺寸受盐浓度与价态的影响,在中等lB范围内,随着单价盐的加入,<Rg2>逐渐减小.而加入少量的高价盐则会引起<Rg2>更加显着得减小,这主要是由于高价反离子的凝聚造成的.对于高价盐,在一定的lB范围内,随着盐浓度的增加,存在<Rg2>先减小后增大的现象.在高价(如二价或三价)盐溶液中,当高价反离子的总电量大于链电量时,高价反离子和共离子(与链带同种电荷的离子)都发生凝聚,而单价反离子几乎不发生凝聚;并且存在高价离子过度补偿引起的链有效电荷反转.The conformational change of polyelectrolyte chains under external stimuli such as temperature, solvent quality, pulling force, or salt, is of critical importance to numerous biological and synthetic processes, as well as to their potential applications. The conformation transition and ion condensation of a strongly charged polyelectrolyte chain in solvent with added salt are studied using parallel tempering Monte-Carlo simulation on a lattice model, focusing on the effects of salt concentration and valence. The variation of the mean-square radius of gyration （〈Rg2〉） with Bjerrum length （lB） is obtained in different salt concentrations and for salts of different valence. It is shown that the chain expands first with increased lB, and then it shrinks and finally the chain assumes a collapse globule conformation. The chain size is related to both the concentration and the valence of the salt. In intermediate range of lB, upon addition of monovalent salt, 〈Rg^2〉 gradually decreases. By contrast, the addition of a multivalent salt leads to a more pronounced decrease in 〈Rg^2〉 and a relatively low lB value for the chain collapse transition. When lB is appropriate, the chain re-expansion is observed with increased concentration of the multivalent salt. In the high multivalent salt solution, condensation of both multivalent counterions and co- ions happens when the charge of total multivalent counterions is greater than that of the chain segments, whereas the univalent counterions hardly condense. For the monovalent salt, the effective charge of chain decreases with increased salt concentration at a given lB. For the multivalent salt, overcompensation of multivalent counterions is observed in appropriate range of lB when salt concentration exceeds a specific value, leading to inversion of effective charge of the chain. The overcompensation of multivalent counterions also leads to condensation of the co-ions. The charge reversal and condensation of co-ions lead to the re-expansion of the chain at a hi

关 键 词：聚电解质 塌缩 高价盐 并行回火 蒙特卡罗 

分 类 号：O631[理学—高分子化学]