【作者】 胡义钰；

【导师】 曹达鹏；

【作者基本信息】 北京化工大学 ， 化学工程， 2009， 硕士

【摘要】 聚电解质—胶体络合物由于其在很多领域内的重要应用,如胶体稳定性,电动力学性质、悬浊液粘性以及生物体系络合物等,已经成为国际上的一个研究热点。本文研究工作包括两个部分:聚电解质的桥链结构对胶体颗粒静态和动态行为的影响和水溶液中非均匀带电的类富勒烯结构的纳米颗粒在平板聚电解质刷上的吸附的布朗动力学(BD)研究。首先基于粗粒度模型我们用布朗动力学模拟的方法考察了以两端带电的聚电解质为媒介的桥链结构对水溶液中胶体的径向分布函数(RDF)和扩散行为的影响。为便于比较,我们还考察了由一端带电的聚电解质与胶体形成的体系的各种相对应的性质。模拟结果显示,当体系浓度较小时两端带电的聚电解质会引起胶体的聚集。这是由于在低浓度的情况下,聚电解质的回转半径小于体系胶体间的平均距离。当两端带电的聚电解质同时吸附在两个不同的胶体上时,聚电解质的桥链作用将主导胶体的RDF及其扩散行为。随着体系浓度的增大,聚电解质的回转半径将大于体系中胶体间的平均距离,这时聚电解质的桥链作用就可以忽略了。通过考察两端带电的聚电解质对胶体静态和动态行为的影响,有助于我们进一步的合成胶体溶液的稳定剂或聚沉剂。另外,随着高分子合成技术的发展,很多具有新结构的聚电解质被合成出来,其中包括一些聚电解质刷子系统。基于粗粒度模型,我们用BD的模拟方法在水溶液中考察了类富勒烯结构的纳米颗粒在平板聚电解质刷上的吸附。模拟发现,整体为电中性的纳米颗粒能够吸附在聚电解质刷上。这是由聚电解质刷对纳米颗粒表面正电区域的吸引和对其负电区域的排斥而引起的静电非对称作用力所导致的。模拟结果显示,当纳米颗粒的偶极矩非常大时,纳米颗粒在主体相中容易发生团聚形成纳米团簇,它的形成不利于纳米颗粒在分子刷上的吸附。当纳米颗粒偶极矩较小时,其吸附量随分子刷嫁接密度的增加而单调递减;但纳米颗粒的偶极矩较大时,其吸附量与分子刷嫁接密度的关系表现为非单调性。另外我们还发现分子刷的嫁接密度是影响分子刷厚度和体系渗透压的一个重要因素。更多还原

【Abstract】 Due to important applications of polyelectrolyte (PE)-colloid system in many fields, such as colloidal stability, electrokinetics, viscosity of suspension and the complexations of biological system, the investigations on PE-colloids systems gain a lot of scientific attention in the last decades. This work contains two sections. One is Brownian dynamics (BD) simulation of the effect of bridging conformation of PEs on static and dynamic behavior of colloids. The other is adsorption of nonuniformly charged fullerene-like nanoparticles on planar PE brushes in an aqueous solution.BD simulation is performed to investigate the effect of the bridging conformation of the PE with two charged heads (two-heads PE) on the radial distribution function (RDF) and diffusion behavior of colloids on the basis of the coarse grained model. For comparison, the system containing colloids and the PE with only one charged head (one-head PE) is also investigated. The simulation results indicate that, at low concentrations, the bridging effect of the two-heads PE chain leads to correlation of colloids. The reason is that at low concentration the gyration radius of the PE chain is less than the average distance between two colloids. When the two-heads PE chains are adsorbed on different colloids, the bridging effect of the PE chain dominates the RDF and diffusion behavior of the colloids. With the increase of the concentration of the system, when the gyration radius of the PE chain is greater than the average distance between two colloids, the bridging effect of the PE chain becomes trivial. By investigating the mechanism of the two-heads PE chain affecting the static and dynamic properties of the colloids, we can provide useful information for the synthesis of stabilizers and destabilizers of colloidal particles.In addition, with the development of the synthesis technology of polymers, a great range of PEs with "vagarious" structures appear, including the PE brush systems. On the basis of the coarse grained model, we investigated the adsorption of nonuniformly charged fullerene-like nanoparticle on planar PE brushes in an aqueous solution by using BD simulation. It is found that the electroneutral nanoparticle can be adsorbed by the PE brush, which is attributed to the asymmetrical electrostatic interactions of the PEB with the positively charged sites and negatively charged sites of the fullerene-like nanoparticle. The simulation results indicated that the adsorption amount exhibits non-monotonic behavior with the dipole moment of nanoparticle. First, the adsorption amount increases with the dipole moment; and then reaches the maximum at the dipole moment ofμ=10.45. Finally the adsorption falls at the dipole moment ofμ=14.39. The reason may be that at the extremely large dipole moment ofμ=14.39, the fullerene-like nanoparticles aggregate together to form a big cluster in the bulk phase. This observation is confirmed by the extremely high peak in the RDF between nanoparticles. Accordingly, it is difficult for nanoparticles to enter into the PE brush at the dipole moment ofμ=14.39. In addition, it is also found that the brush grafting density is an important factor affecting the brush thickness and the osmotic pressure.更多还原