本文選題：分子動(dòng)力學(xué) + 聚電解質(zhì)刷　； 參考：《中國(guó)民航大學(xué)》2017年碩士論文

【摘要】：作為一種極具發(fā)展?jié)摿Φ母叻肿芋w系,聚電解質(zhì)刷被廣泛應(yīng)用在生物和材料科學(xué)等領(lǐng)域。對(duì)聚電解質(zhì)刷的研究具有重要的科學(xué)意義與應(yīng)用前景。本文采用分子動(dòng)力學(xué)方法,對(duì)接枝在兩相對(duì)平板上的有限尺寸聚電解質(zhì)刷在良溶劑中的靜態(tài)和動(dòng)態(tài)行為進(jìn)行了研究。主要內(nèi)容及研究結(jié)果如下:(1)聚電解質(zhì)刷的靜態(tài)行為板間距固定時(shí),研究了抗衡離子價(jià)態(tài)、聚電解質(zhì)鏈的接枝密度和帶電分?jǐn)?shù)對(duì)聚電解質(zhì)刷靜態(tài)行為的影響。研究表明,抗衡離子價(jià)態(tài)的增加能夠引起聚電解質(zhì)刷的塌縮轉(zhuǎn)變。相對(duì)于單價(jià)抗衡離子,多價(jià)抗衡離子與聚電解質(zhì)鏈的關(guān)聯(lián)作用更強(qiáng),多價(jià)抗衡離子的這種關(guān)聯(lián)作用是聚電解質(zhì)刷塌縮的驅(qū)動(dòng)力。接枝密度的增加會(huì)引起刷高度的線性增加,且三價(jià)抗衡離子情況中刷高增加得更快。此外,在三價(jià)抗衡離子體系中,當(dāng)鏈帶電分?jǐn)?shù)較小時(shí),聚電解質(zhì)刷隨帶電分?jǐn)?shù)的增加而伸展。當(dāng)帶電分?jǐn)?shù)繼續(xù)增加時(shí),刷轉(zhuǎn)而開(kāi)始塌縮。(2)聚電解質(zhì)刷的動(dòng)態(tài)行為通過(guò)改變板間距D,研究了三價(jià)抗衡離子情況中聚電解質(zhì)刷的動(dòng)態(tài)行為。研究表明,靜電相互作用和體積排斥作用之間的相互競(jìng)爭(zhēng)決定了聚電解質(zhì)刷的動(dòng)態(tài)行為。多價(jià)抗衡離子與接枝在不同板上的聚電解質(zhì)鏈之間的橋接作用對(duì)刷高和壓強(qiáng)有著重要影響。板間距較大時(shí)(32D/σ44),隨著板間距的減小,刷高輕微降低,壓強(qiáng)輕微增加。此時(shí)兩刷沒(méi)有交疊,刷的性質(zhì)由兩刷之間的長(zhǎng)程靜電排斥作用決定。隨著兩刷進(jìn)一步靠近(28D/σ32),刷高增加,壓強(qiáng)減小。此時(shí)兩刷開(kāi)始交疊,刷的性質(zhì)由抗衡離子與帶電刷之間的橋接作用決定。當(dāng)板間距較小時(shí)(10D/σ28),刷高顯著降低,壓強(qiáng)劇烈增加。此時(shí)兩刷交疊程度很大,體積排斥作用成為主導(dǎo)。相對(duì)于無(wú)限大的平板刷,有限尺寸聚電解質(zhì)刷的自由度更大,導(dǎo)致其末端單體密度分布,刷高,橋接系數(shù)和壓強(qiáng)隨板間距的變化與無(wú)限尺寸體系不同。有限尺寸聚電解質(zhì)平板刷體系與實(shí)驗(yàn)中的真實(shí)體系更相似,所得結(jié)論將對(duì)以后的實(shí)驗(yàn)研究具有一定的指導(dǎo)意義。
[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.
【學(xué)位授予單位】：中國(guó)民航大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：O631

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本文編號(hào)：1774968