有限尺寸聚电解质平板刷的模拟研究

发布时间：2018-04-19 22:14

本文选题：分子动力学 + 聚电解质刷　；参考：《中国民航大学》2017年硕士论文

【摘要】：作为一种极具发展潜力的高分子体系,聚电解质刷被广泛应用在生物和材料科学等领域。对聚电解质刷的研究具有重要的科学意义与应用前景。本文采用分子动力学方法,对接枝在两相对平板上的有限尺寸聚电解质刷在良溶剂中的静态和动态行为进行了研究。主要内容及研究结果如下:(1)聚电解质刷的静态行为板间距固定时,研究了抗衡离子价态、聚电解质链的接枝密度和带电分数对聚电解质刷静态行为的影响。研究表明,抗衡离子价态的增加能够引起聚电解质刷的塌缩转变。相对于单价抗衡离子,多价抗衡离子与聚电解质链的关联作用更强,多价抗衡离子的这种关联作用是聚电解质刷塌缩的驱动力。接枝密度的增加会引起刷高度的线性增加,且三价抗衡离子情况中刷高增加得更快。此外,在三价抗衡离子体系中,当链带电分数较小时,聚电解质刷随带电分数的增加而伸展。当带电分数继续增加时,刷转而开始塌缩。(2)聚电解质刷的动态行为通过改变板间距D,研究了三价抗衡离子情况中聚电解质刷的动态行为。研究表明,静电相互作用和体积排斥作用之间的相互竞争决定了聚电解质刷的动态行为。多价抗衡离子与接枝在不同板上的聚电解质链之间的桥接作用对刷高和压强有着重要影响。板间距较大时(32D/σ44),随着板间距的减小,刷高轻微降低,压强轻微增加。此时两刷没有交叠,刷的性质由两刷之间的长程静电排斥作用决定。随着两刷进一步靠近(28D/σ32),刷高增加,压强减小。此时两刷开始交叠,刷的性质由抗衡离子与带电刷之间的桥接作用决定。当板间距较小时(10D/σ28),刷高显著降低,压强剧烈增加。此时两刷交叠程度很大,体积排斥作用成为主导。相对于无限大的平板刷,有限尺寸聚电解质刷的自由度更大,导致其末端单体密度分布,刷高,桥接系数和压强随板间距的变化与无限尺寸体系不同。有限尺寸聚电解质平板刷体系与实验中的真实体系更相似,所得结论将对以后的实验研究具有一定的指导意义。
[Abstract]:As a potential polymer system, polyelectrolyte brushes are widely used in biology and material science. The study of polyelectrolyte brushes has important scientific significance and application prospect. In this paper, the static and dynamic behaviors of a finite size polyelectrolyte brush grafted on two relative plates in a good solvent were investigated by molecular dynamics method. The main contents and results are as follows: (1) when the static behavior plate spacing of the polyelectrolyte brush is fixed, the effects of ion valence state, graft density of the polyelectrolyte chain and charged fraction on the static behavior of the polyelectrolyte brush are studied. The results show that the increase of valence state of counterweight ions can cause collapse transition of polyelectrolyte brushes. Compared with univalent countervailing ions, polyvalent countervailing ions have stronger correlation with polyelectrolyte chains, which is the driving force of the collapse of polyelectrolyte brushes. The increase of grafting density leads to a linear increase in brush height and a faster increase in brush height in the case of trivalent countervailing ions. In addition, when the charge fraction of the chain is small, the polyelectrolyte brush is extended with the increase of the charged fraction in the trivalent countervailing ion system. When the charged fraction continues to increase, the dynamic behavior of the polyelectrolyte brush begins to collapse. The dynamic behavior of the polyelectrolyte brush in the case of trivalent countervailing ions is studied by changing the plate spacing. It is shown that the dynamic behavior of polyelectrolyte brushes is determined by the competition between electrostatic interactions and volume repulsions. The bridging action between polyvalent countervailing ions and polyelectrolyte chains grafted on different plates has an important effect on brush height and pressure. When the plate spacing is larger, the brush height decreases slightly and the pressure increases slightly with the decrease of the plate spacing. There is no overlap between the two brushes. The nature of the brushes is determined by the long-range electrostatic repulsion between the two brushes. With the two brushes closer to 28D / 蟽 32, the brush height increases and the pressure decreases. At this time, the two brushes begin to overlap, the nature of the brush is determined by the bridging action between the counterbalance ion and the brush. When the plate spacing is smaller than 10 D / 蟽 28, the brush height decreases significantly and the pressure increases sharply. At this time, the overlap between the two brushes is very large, and the volume repellent effect becomes dominant. Compared with the infinite plate brushes, the finite polyelectrolyte brushes have greater degrees of freedom, which leads to the difference between the terminal monomer density distribution, the brush height, the bridging coefficient and the pressure with the plate spacing. The finite size polyelectrolyte plate brush system is more similar to the real system in the experiment.
【学位授予单位】：中国民航大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O631

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