流体动力学作用对粒子聚集影响的布朗动力学模拟

采用布朗动力学模拟方法, 研究了流体动力学作用对稀溶液中悬浮粒子聚集过程的影响. 模拟中忽略了一个粒子同时与多个粒子碰撞聚集的可能, 引入了前人有关两粒子间流体动力学作用影响的研究成果. 模拟结果证实了流体动力学的作用在比较大的幅度上减缓了粒子的聚集过程, 是导致粒子聚集速率的实验值低于Smoluchowski理论值的重要原因之一. 另外, 在分别加入和排除重力作用, 以及考虑和忽略粒子间流体动力学作用在内的各种条件下模拟了粒子的聚集过程, 得到了两种因素相互耦合作用时各因素对粒子聚集过程影响的结果, 并从动力学的角度对这些因素的影响机制进行了相应的讨论.     

纳米粒子填充聚合物体系中凝聚结构和渗流转变的分子动力学模拟

通过粗粒化模型,采用分子动力学模拟的方法研究了纳米粒子填充聚合物体系中粒子的凝聚过程.结果表明:纳米粒子和基体粒子间的相互作用决定了团聚体的结构,且作用力越大则团聚体的分形维数越高,当粒子的相互作用强度(εNP)为1.0时,模拟体系中团聚体的分形维数为2.05,与聚酰亚胺炭黑体系透射电镜照片结果一致.对渗流过程的模拟结果表明,相互作用力的增大会导致渗流时间的增加,渗流转变速率减慢,与动态电渗流实验的实测结果相符合.     

范德华作用和静电作用下的二元粒子自组装

采用简单粗粒化粒子模型,通过郎之万动力学模拟研究了具有范德华作用和静电作用的二元粒子自组装．研究发现,通过改变粒子尺寸和粒子间作用强度,二元粒子能够自发形成各种聚集结构,如球形、堆叠层状与管状结构．利用两亲性分子或两嵌段聚合物自组装理论,解释了二元粒子聚集结构的形成规律．当向溶液中加入反电荷离子时,模拟表明粒了聚集结构在相图中的分布出现了明显偏移．     

受限于平行板中高分子刷/磁性纳米粒子体系的构象性质研究

采用蒙特卡洛模拟方法研究了在外磁场作用下磁性纳米粒子/高分子刷组成的共混体系的统计构象性质.共混体系受限于两平行板之间,高分子刷—端随机嫁接在乎行板上,另一端自由生长,高分子刷与高分子刷之间以及磁性纳米粒子与磁性纳米粒子之间存在相互排斥作用,而高分子刷和磁性纳米粒子之间存在相互吸引作用,所施加的磁场方向与两平行板垂直....     

Lennard-Jones流体气液相图的粒子交换分子动力学模拟研究

利用粒子交换分子动力学模拟方法(Particle exchange molecular dynamics,PEMD)研究了Lennard-Jones流体的气液相图．模拟中,用两个耦合箱分别代表液相和气相．通过直接比较两箱的粒子化学势来控制交换粒子,从而达到两相平衡．采用Widom方法计算化学势．两模拟箱平衡时具有相同的温度、压强和粒子化学势．模拟的气液相图结果与利用其它方法得到的Lennard-Jones流体气液相图符合得很好．     

在平行板受限条件下AB两嵌段共聚物/纳米粒子复合物自组装行为的Monte Carlo模拟

采用Monte Carlo模拟方法研究了在平行板受限条件下A_(15)B_5非对称两嵌段共聚物与纳米粒子复合物的自组装行为,其中平行板对多组分嵌段A具有吸引相互作用.模拟结果表明,纳米粒子在两嵌段共聚物/纳米粒子复合物中的体积分数、嵌段共聚物不同嵌段与纳米粒子间的相互作用均对体系在平行板受限条件下的形貌结构及纳米粒子在体系中的分布有重要影响.当平行板间距一定时,未添加纳米粒子的A_(15)B_5非对称两嵌段共聚物中的A嵌段被吸附在平行板上形成层状相,而B嵌段则在平行板中形成六角堆积穿孔层状结构.加入与A嵌段不相容而与B嵌段相容的纳米粒子后,增加了纳米粒子与B嵌段的相容性,有利于保持B嵌段所形成的穿孔结构及孔洞尺寸,同时纳米粒子能够均匀地分散在B相区中.当引入的纳米粒子与A和B两嵌段均不相容时,降低纳米粒子与嵌段共聚物的不相容性同样有利于维持体系的穿孔结构.当纳米粒子与AB两嵌段共聚物间的排斥作用微弱时,即使含量较高,纳米粒子也不聚集,并且均匀分布在A相区与B相区的交界处.     

梳型嵌段共聚物微观相分离的耗散粒子动力学模拟

利用耗散粒子动力学(Dissipative particle dynamics, DPD)模拟方法研究了二维梳型嵌段共聚物的微观相分离, 得到了相形貌与侧链长度及链段间相互作用的依赖关系, 进一步与线型和星型嵌段共聚物微观相分离进行了对比. 模拟结果揭示了本体中影响梳形嵌段共聚物微观相分离的主要因素, 包括嵌段共聚物的组成\, 拓扑结构以及不同粒子间的排斥力.     

纳米粒子/共聚物混合体系结构的Monte Carlo模拟

基于简立方格点模型,对纳米粒子/共聚物混合体系进行了动力学Monte Carlo模拟研究. 每一共聚物链均由一个A珠子和三个B珠子组成,表示为A1B3. A1B3链的两亲性体现为B-B之间的相互吸引作用,同时憎水性的纳米粒子之间也存在相互吸引. 通过适当选取纳米粒子与B珠子之间的吸引作用势,观察到两种结构:纳米粒子/A1B3链的核-壳结构和纳米粒子分散在憎水壳层中的A1B3囊泡结构. 还研究了这两种结构的动力学演化过程,模拟结果表明在纳米粒子分散于囊泡壳层的过程中A1B3囊泡起模板作用.     

耗散粒子动力学和纳维边界条件在微米纳米流体力学模拟中的应用

耗散粒子动力学是一种粗粒化的计算模拟方法,在微米和纳米流体力学中有着广泛的应用.由于界面在微小体积流体中的重要性,边界条件的选取在微米和纳米流体的研究中起到了关键性的作用.我们简单地介绍了耗散粒子动力学的模拟方法,并以此为基础,介绍了能够实现纳维边界条件的可调滑移长度的边界条件模拟方法.通过条纹状图案修饰的超疏水表面的流体力学行为研究,和高分子链在微米纳米流体器件中的运动研究2个例子,耗散粒子动力学结合纳维边界条件的模拟方法的实用性和可靠性得到了证实.     

磷脂微滴囊泡化的介观模拟

发展了一种非显示溶剂的粗粒化三粒子磷脂模型,该模型明确反映磷脂分子的双尾结构．模型分别采用变形的MIE作用势和Harmonic作用势描述分子间非成键和分子内成键相互作用,粗粒化力场参数通过拟合DPPC双分子层的结构和力学性质获得．该粗粒化模型成功重现了磷脂分子从随机初始态到双分子层和从盘状结构到囊泡的形成过程．应用该模型系统研究了球形和柱形磷脂微滴囊泡化的过程,结果表明此模型能有效地模拟介观尺度下复杂磷脂囊泡的形成及演化．     

COMPUTER SIMULATION OF POLYMER SOLUTION THERMODYNAMICS

The statistical counting method for the computer simulation of the ther-modynamic quantities of polymer solution has been reviewed. The calculating results fora single athermal chain confirm the theory of the renormalization group. The results forthe athermal solution are consistent with the scaling law of the osmotic pressure with theexponent 2.25. The results for a single chain with the segmental interaction are in a goodagreement with the exact results obtained by the direct counting method. The results forthe polymer solution show us that the Flory-Huggins parameter is strongly dependent onboth the polymer concentration and the interaction energy between segments. Monte carlo simulation; Polymer solution; Thermodynamic quantities;Translational entropy; Conformational entropy; Scaling law     

柔性高分子/小分子液晶混合物的自洽场理论

发展了柔性高分子/小分子液晶混合物连续自洽场理论，将小分子液晶模型化 为取向与位置无关的单体分子，小分子液晶间存在各向异性的Maier-Saupe相互作 用，该理论可还原成高分子和各向同性小分子组成的Flory-Huggins溶液理论和纯 液晶的Maier-Squpe液晶理论，通过数值解自洽场方程组，还将理论用于研究柔性 高分子/小分子液晶混合物相分离开界面性质，得到的结果与用Helfand格子界面理 论和MOnte Carlo模拟的结果一致。     

Interactions between nanocolloidal particles in polymer solutions: effect of attractive interactions

We present a density-functional theory study of nanoparticle interactions in a concentrated polymer solution. The polymers are modeled as freely jointed tangent chains; all nonbonded interactions between polymer segments and nanoparticles are described by Lennard-Jones potentials. We test several recently proposed methods of treating attractive interactions within the density-functional theory framework by comparing theoretical results with recent simulation data. We find that the simple van der Waals approach provides the most accurate results for the polymer-mediated potential of mean force between two dilute nanoparticles. We employ this approach to study nanoparticle interactions as a function of nanoparticle-segment interaction strength and polymer solution density and temperature.     

Effect of large deformation and material nonlinearity on the JKR (Johnson–Kendall–Roberts) test of soft elastic materials

We study in detail the effect of large deformation and material nonlinearity on the JKR (Johnson–Kendall–Roberts) theory of adhesive contact for two systems. The first is a Neo‐Hookean hemisphere in adhesive contact with a smooth rigid substrate. The second is a smooth rigid spherical indenter in adhesive contact with a Neo‐Hookean half space. We show that our results are special cases of a general theory that models large deformation adhesive contact of spherical lenses. This theory shows that the solution of any large deformation JKR (LDJKR) problem can be obtained from the solution of a corresponding large deformation Hertz (LDH) problem. Using this theory, we extend the small strain JKR theory to the large deformation regime, the only restriction being that the materials are nonlinear elastic or hyperelastic. The adhesive contact problem for the two systems is solved using two methods. In method one, the LDJKR theory is obtained using finite element simulation results for a corresponding LDH problem; in method two, we solve the adhesive contact problems directly using a cohesive zone model to quantify adhesive interaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2912–2922, 2006     

Potential energy surfaces and dynamics of Ni2+ ion aqueous solution: molecular dynamics simulation of the electronic absorption spectrum

We develop a model effective Hamiltonian for describing the electronic structures of first-row transition metals in aqueous solutions using a quasidegenerate perturbation theory. All the states consisting of 3d(n) electronic configurations are determined by diagonalizing a small effective Hamiltonian matrix, where various intermolecular interaction terms such as the electrostatic, polarization, exchange, charge transfer, and three-body interactions are effectively incorporated. This model Hamiltonian is applied to constructing the ground and triplet excited states potential energy functions of Ni(2+) in aqueous solution, based on the ab initio multiconfiguration quasidegenerate perturbation theory calculations. We perform molecular dynamics simulation calculations for the ground state of Ni(2+) aqueous solution to calculate the electronic absorption spectral shape as well as the ground state properties. Agreement between the simulation and experimental spectra is satisfactory, indicating that the present model can well describe the Ni(2+) excited state potential surfaces in aqueous solution.     

N-(1-萘基)琥珀酰亚胺分子间相互作用的计算机模拟

对分子间相互作用比较复杂的N-(1-萘基)琥珀酰亚胺进行理论计算时, 提出了将溶液构建和随机构象搜索相结合的多分子相互作用体系构建方法, 可以简单而准确地得到二聚体和三聚体结构, 其中二聚体结构和采用分子对接方法得到的结果完全一致. 经密度泛函理论计算, 得到了在真空条件下二聚体结构的最低能量构象. 对较大体系的三聚体结构采用高精度分子力学进行了理论计算. 通过分子间相互作用对分子构象的影响讨论了溶液结晶过程中N-(1-萘基)琥珀酰亚胺分子构象变化, 为该化合物结晶机理的深入研究提供重要依据.     

电解质溶液的分子热力学模型研究进展

"本文从经典溶液理论及半经验模型、近代统计力学理论和分子模拟三大方面阐述了近年来国内外电解质溶液热力学的研究进展。指出电解质溶液的研究已逐渐从经典的溶液理论和半经验模型转向用统计力学理论进行研究, 从电解质的原始模型转向非原始模型。从分子和离子的微观参数出发建立高水平的热力学理论模型, 以预测电解质溶液体系的宏观热力学性质, 是发展的必然趋势。     

Solvent size effect on the depletion layer of a polymer solution near an interface

By varying polymer concentration phi0p and Flory-Huggins parameter chi, the effect of solvent size on the depletion interaction between polymer coils and a hard wall was investigated by the real-space version of self-consistent field theory (SCFT). The depletion profiles and depletion thickness indicated that the depletion effect is strong in less good solvent with large molecular volume. Through the analysis of the respective free energies of polymer coils and solvent molecules, we found that the increment in the translation entropy of the solvent is the key to strengthening the depletion interaction. On the basis of the SCFT results, we define a solvent with volume about one to six times that of the polymer segment as a "middle-sized solvent". The density oscillations previously studied by Van der Gucht et al. and Maassen et al. were also observed in our simulation, and the addition of middle-sized solvent will magnify the amplitude of the oscillations. The solvent-size-dependent depletion interaction may be an explanation for the reduced entanglement and promoted crystallization behavior of polymer coils prepared from the solution with middle-sized solvent.     

The role of local structure on formic acid decomposition in supercritical water: A hybrid quantum mechanics/Monte Carlo study

We explored water-assisted decompositions of formic acid in supercritical water in terms of local structure near reactant. A hybrid quantum mechanics/molecular mechanics (QM/MM) simulation used in this paper includes QM part as first solvation shell members around the reactant. A present QM/MM approach can simulate supercritical water solution with a reasonable computational load while keeping the simulation preciseness because a density functional theory of B3LYP/6-31+G(d) level was iterated at every 1000 Monte Carlo solute moves. The formic acid converts mainly decarboxylation by water-assisted mechanism, and the coordinated water molecules play an important role for understanding supercritical water density dependence of the reaction. We analyzed a contour map based on the solute–solvent interaction energy along with the reaction pathway. Coordinated water molecule restricted the dehydration pathway by means of hydrogen bond with formic acid, however, the coordinated water promotes the decarboxylation pathway by means of stabilization of the transition state structure with one catalytic water molecule. The contour map of the pair interaction energy along the reaction path elucidates the role of local structure on reactions in supercritical water.