【作者】 杨洋；

【导师】 左春柽；

【作者基本信息】 吉林大学 ， 机械设计及理论， 2014， 博士

【摘要】 聚合物刷是指通过物理吸附或者化学键的方式附着在特定表面并呈现一定形貌的一层聚合物。聚合物刷的物理化学性质及构象决定了其润湿特性、腐蚀特性、胶体稳定性、表面智能及生物传感特性，聚合物刷也凭借这些特性被广泛应用于日常生活中。二嵌段共聚物刷在纳米表面的图案控制领域也具有广阔的应用前景。与实验和理论相对比，计算机模拟能够对这些系统的物理吸附过程进行可视化研究，从而帮助理解这类吸附过程中所发生现象的本质。因此研究二嵌段共聚物在金属表面的吸附具有重要的科学意义和应用前景。本文基于分子模拟方法重点研究了不同性质的二嵌段共聚物（包括中性的二嵌段共聚物、带电的二嵌段共聚物以及不同刚度和温度情况的二嵌段共聚物）在不同金属晶体表面附着的情况，讨论了球形颗粒表面接枝两性聚电解质形成的聚合物刷的构象性质。此外，深入研究电荷序列和接枝密度对两性聚电解质在球形颗粒表面的构象特性。细致地分析了二嵌段共聚物在金属表面吸附的物理机制，并且发现了一些独特的现象。本文主要研究内容如下：（1）从分子尺度阐述了中性二嵌段共聚物在面心立方体表面的吸附性质。研究了A-block和B-block单体数量大小对于吸附特性的影响。本文模拟了二嵌段共聚物链的单体总量固定的情况下，增加A-block单体在聚合物链中的比例；以及A-block单体数量固定，增加B-block单体数量的情况。研究结果表明当二嵌段共聚物链单体数量固定时，聚合物链的吸附率随A-block单体数量的增加而增加，当A-block单体数量占总量的1/2时，吸附率达到最大值，随着A-block单体数量继续增加，吸附率缓慢减小。然而当A-block的单体数量固定时，聚合物链的吸附率将随着B-block单体数量的增加而减小，当B-block单体的数量增加到A-block单体数量的6倍时，继续增加B-block单体的数量其吸附率将保持不变。（2）揭示了带电二嵌段共聚物链在面心立方体表面的吸附机理。研究了带电的二嵌段共聚物链在B-block单体带电量情况下的吸附特性。结果表明带电二嵌段共聚物在表面形成的刷的结构和反离子浓度的分布依都赖于A-block单体的数量。虽然带电二嵌段共聚物链模型中A-block和B-block所占比例与第二章相同，但是在反离子作用情况下，当链中单体总量一定，吸附率将随着A-block的增加而不断升高。反之，当A-block数量固定时，B-block单体数量的增加对吸附率的影响并不显著。这说明系统中的反离子数量对带电二嵌段共聚物链的吸附特性有一定的影响。（3）揭示了不同刚度条件下的A-block和B-block对于整个二嵌段共聚物链在六方紧密堆积体表面的吸附机理。研究了三种不同的二嵌段共聚物链模型条件下的吸附率，其中A-block单体数量与二嵌段共聚物单体数量的比分别是1/2、2/3和1/3。同时也研究了当两种嵌段分别为柔性条件下，另外一种嵌段为柔性链、半柔性、刚性和棒状条件下，吸附率的变化情况。结果表明当A-block占总量的1/2时，二嵌段共聚物的吸附率随A-block刚度的增加先升高后降低。反之随着B-block刚度的增加，吸附率先升高后降低再缓慢升高。当A-block占总量的2/3的时候，A-block刚度增加的过程中吸附率迅速降低，而后随着A-block刚度继续增加而保持不变，B-block刚度增加的过程中吸附率未发生明显变化。当A-block占总量的1/3的时候，A-block的刚度增加，吸附率随之降低，而B-block刚度增加的时候吸附率则是缓慢降低而后又缓慢升高。（4）对比不同势能情况下的吸附机理变化情况，通过势能与温度之间的关系，总结出温度对于二嵌段共聚物链在HCP晶体表面吸附的促进作用。（5）研究了半柔性、柔性和刚性的两性聚电解质球形刷的构象变化及其结构特征。对于其中接枝的两性聚电解质链，分别讨论了其在柔性、半柔性和刚性条件下的平均末端距、净电荷密度还有径向分布函数在多种接枝密度和电荷序列情况下的变化。模拟得到的最终稳定状态下的构象截图，对构象性质的分析发挥了重要的作用。证明了当电荷序列α=1时，接枝密度的变化对末端距不会产生影响。但是当电荷序列α降低的时候，其末端距将会随着接枝密度的增加而相应的降低。同时当α=1/20并且接枝密度为ρg=0.0442-2的时候，末端距降低到最小值，即使接枝密度继续升高末端距也不会再继续降低。而对于gNmPm(r1)和gNmPc(r1)两种径向分布函数在不同接枝密度情况下，可以明显观察出在接枝密度对于径向分布函数的影响并不明显，影响这两种径向分布函数的主要因素是电荷分布序列的变化。同时电荷分布序列也是影响带负电荷单体和带正电荷反离子径向空间分布的主要因素。证明了接枝密度和电荷序列分别对净电荷密度曲线的振荡幅度以及振荡周期产生较大的影响。当两性聚电解质链为柔性的时候，几乎所有接枝在球形颗粒表面的两性聚电解质链都塌缩在球形颗粒表面。而刚性的两性聚电解质链系统中，在较低接枝密度条件下两性聚电解质链的构象几乎不发生变化，随着接枝密度的增加末端单体之间的距离减小，在α=1/20时静电吸引发挥作用使得在球形颗粒表面发生折叠的两性聚电解质链的数量的增加。更多还原

【Abstract】 Polymer brush is a layer of polymers attached with one end to a surface either throughphysical adsorption or chemical bond. The polymer brushes exist in everyday life, much ofthe application polymer brushes originated from their different properties, wetting, corrosion,colloidal stabilization, smart surfaces and biological sensors. In the surfaces with controllablepatterns on a nanometer scale, diblock copolymer brushes have wide application prospects.Compared to experiments and theories, computer simulations can provide a directvisualization on the physical process, and further help us understanding the essence ofphenomena with adsorbing process. Therefore, the investigations of diblock copolymeradsorbed on metal crystal surface have important scientific interest and practical value.In the present work, the case of the surface with different metal crystal attached variousdiblock copolymer (including neutral diblock copolymer, charged diblock copolymer, anddiblock copolymers with various stiffness and temperature) are studied based on molecularsimulation methods, as well as the conformation of polyampholyte chains grafted on thespherical particle is discussed. Additionally, deep investigations into polyampholytes graftedonto spherical particle for interaction between colloids, preventing macromolecules andparticles adsorbing on the surface are of great significance on understanding of the nature oflife activity. In this work, the physics mechanism of diblock copolymer adsorbing on themetal crystal surface were analyzed extensively, and some interest phenomena were found.The main contents are listed as follows:（1）We used molecular dynamics simulations to study the adsorption properties ofneutral diblock copolymer on surface of face centered cubic. The effect of A-block andB-block size of number of monomers for the adsorption characteristics were studied. Whenthe total quantity of monomers of diblock copolymer chains is fixed, an increase in the number of A-block monomer will cause an increase in adsorption rate. When the number ofA-block monomer is fixed, analyze the amount of adsorption with increasing the number ofB-block monomer. It has been found that if the number of monomers in one chain is fixed, theincrease in the number of monomer A-block during adsorption would cause an increase inadsorption rate. And when the A-block monomer amount accounted for1/2of the totalamount, the maximum adsorption rate occurred. However, a further increase in the amount ofA-block monomers would cause slowly decrease in adsorption rate. For the other conditions,a fixed amount of monomer A-block with an increasing amount of B-block would result in anincrease in adsorption rate. Nevertheless, when the number of B-block A-block monomer to6times the number of monomers, the increase in the number of B-block monomer adsorptionrate will remain unchanged.（2）The adsorption mechanism of charged diblock copolymer on the surface of facecentered cubic. The effect of A-block and B-block differently charged for the adsorptioncharacteristics were studied. The result showed that charged diblock copolymer brushesstructure and counterion concentration depends on the number of A-block monomer. Themodel of diblock copolymer chains are the same as the second section, but in the case ofcounterions, at the diblock copolymer chains fixed quantity of monomer, the adsorption rateincreasing as the number of A-block monomers increases. Conversely, the number of A-blockmonomers was fixed, that the adsorption rate does not change significantly with the numberof B-block monomers increase. This shows that the number of counterions is of influence onthe adsorption at the system.（3）Reveals the adsorption mechanism of the diblock copolymer chains on thehexagonal close-packed with different stiffness of A-block or B-block. The adsorption rate ofthree different model diblock copolymers were studied, the ratio of the amount monomer ofA-block and diblock copolymer is1/2,2/3,1/3. Simultaneously, also studied the case ofA-block and B-block as flexible block respectively, the other block as semiflexible, stiff,rod-like the adsorption rate were discussed. The results showed that when the ratio of theamount monomer of A-block and diblock copolymer is1/2, the adsorption rate firstly increased and then decreased with the increasing stiffness. On the contrary, the adsorption ratefluctuated when the stiffness of B-block increases. When the ratio of the amount monomer ofA-block and diblock copolymer is2/3, the adsorption rate decreased with the increasingstiffness of A-block and then the adsorption rate remain unchanged. When the ratio of theamount monomer of A-block and diblock copolymer is1/3, the adsorption rate decreasedwhen the stiffness of A-block increases, and adsorption rate decreased and then slowlyincreased.（4）Comparison of adsorption mechanism with different potential, through therelationship between potential energy and temperature, summed up with the increase intemperature could promote the adsorption of diblock copolymer chains.（5）Study conformation changes and structural features of polyampholyte sphericalbrushes. The polyampholyte chains grafted on the spherical particles, we discussed theaverage distance of end monomers with various grafting density，charge sequence and netcharge density situations. And the final steady state conformation was obtained, the analysisof conformational properties play an important role. Proves the grafting density variations donot affect the distance of end monomers at α=1. However, when the charge sequence αdecreases, the distance of end monomers would decreases as the grafting density increased.When α=1/20and ρg=0.0442-2, the distance of end monomers reduce to minimum, even ifthe grafting density continues to rise, the distance of end monomers would not decrease. Tworadial distribution function at different grafting densities for gNmPm(r1) and gNmPc(r1),respectively. The simulation results can be clearly observed that the impact of the graftingdensity for the radial distribution functions. The impact of two radial distribution functions ofthe main factors was the various charge sequences. The charge sequence is also a major factorfor negatively and positively counterions monomer radial space distribution. Proved thegrafting density and charge sequence impact on the oscillation amplitude and oscillationperiod of net charge density curve. All of the polyampholyte chains collapsed the surface ofspherical particles, when the polyampholyte chains are flexible. However, the polyampholytechains are stiff, the conformational of the polyampholyte chains almost no change, the distance between the start and end monomers decreasing as the grafting densities increasing,at α=1/20the electrostatic attraction play a role, the increase in number of folding of thepolyampholyte chains.更多还原