【作者】 徐嘉靖；

【导师】 杨玉良；

【作者基本信息】 复旦大学 ， 高分子化学与物理， 2005， 博士

【摘要】 由于在稳定粒子分散体系、改善表面润湿性能、提高材料的生物相容性等方面得到广泛的应用，高分子刷体系一直是理论和实验研究的热点。在高分子刷体系中，当粒子和接枝高分子链的尺寸在同一数量级时，接枝面不能被看成无限大的平面。高分子刷侧向均匀的假设不再合理，接枝点的分布将随着粒子和高分子刷相对位置变化而变化。这种情况，只符合接枝点可以迁移的液体刷体系。实际上，大多数高分子刷的接枝点位置是不能移动的，即固体刷更符合实际情况。因而，用于研究这类体系的理论方法，应该能够同时考虑液体刷和固体刷。我们将接枝点密度分布作为限制条件，引入到自洽场方程中，使得自洽场理论能够处理固体刷和液体刷。用该方法研究了曲率为零的平板刷与有限尺寸的惰性粒子之间、粒子尺寸与接枝高分子链的尺寸相当的球形刷子之间以及星形高分子之间的相互作用。第二章中，我们研究了平板刷和圆柱形粒子之间的相互作用，忽略了体系中可能存在的各种焓的相互作用。考察了粒子形状和尺寸，以及接枝参数对粒子与刷子之间作用的影响。得到了如下一些结果：（1）液体高分子刷与粒子相互作用的力／距离曲线上存在一个最大阻力，而固体刷与粒子相互作用的力／距离曲线上，随着体系参数不同，相应地出现极大值点或拐点。（2）当粒子与接枝面之间的距离较远时，参数相同的液体刷或固体刷与粒子之间的作用没有明显差别。（3）力／距离曲线上出现拐点或极值时阻力大小及对应的粒子位置能够反映粒子和刷子的结构特征：其大小与粒子的体积、接枝密度、链长的倒数线性关系；该点出现时，粒子离接枝面的距离与刷子高度的比值为常数（约为1.1）。第三章中，我们研究了在熔体介质中两个完全相同的球形高分子刷之间的相互作用。我们忽略了体系中可能存在的各种焓相互作用，考察了接枝密度、自由链链长、粒子尺寸对球形固体刷或液体刷之间的相互作用的影响。研究的结果表明：（1）当接枝链和粒子的尺寸相当时，高分子刷的结构对粒子尺寸、接枝密度、自由链长度等参数很敏感，在一定的参数范围内，发生“干一湿”转变。（2）改变自由链长度、粒子尺寸以及接枝密度等参数，球形刷子之间的相互作用会发生从完全排斥到近距离排斥、远距离吸引的转变；吸引作用随接枝密度、自由链长度以及粒子尺寸的增加而增强。（3）球形刷子之间吸引的原因在于自由链从受限的刷子附近的区域到达自由的本体中获得的构象熵。（4）当刷子之间的距离较远时，固体刷或液体刷之间的作用从完全排斥变为近距离排斥、远距离吸引的行为是基本一致的，当刷子之间的距离很近时，液体刷之间的排斥作用比固体刷之间的排斥作用弱。星形高分子作为曲率极高的球形高分子刷，同时具有柔性高分子和硬球粒子的性质，在高分子物理和粒子物理两个领域之间建立了一种自然的桥梁，是很重要的模型体系。因此，在第四章中，我们研究了无热溶剂中规则星形高分子之间的相互作用。得到了星形高分子之间的等效二体作用势，当星形高分子之间的距离小于星形高分子的等效软球尺寸时，该作用势与标度理论推测得到的作用势一致，可以表示为：U（d）∝-f^3/2In（d/R）。此外，我们还研究了共线的三个星形高分子之间的三体作用，发现三体作用为微弱的吸引作用，其作用的强度不及二体相互作用的10％，这一结果支持以二体作用势为基础的基于粒子的模拟方法的合理性。更多还原

【Abstract】 End-grafting polymers onto particle surfaces has always been a spotlight in both experimental and theoretical researches for its extensive applications in stabilizing particle dispersion systems, improving biocompatibility of materials, and modifying wetting properties of surfaces, etc. In the field of polymer brushes, the hypothesis of lateral homogeneity of grafting density, which has perfectly explained the behaviors of liquid brushes with mobile grafting sites, however, fails to apply to systems where the size of particles being of the same order as that of the grafting polymers. It becomes even more debatable for real situations in which the polymer brushes bear closer resemblance to a solid brush, where the grafting sites are immobile. To clarify these issues, we develop self-consistent field theory (SCFT) for polymer brushes to address both the liquid and solid cases.We first explore the interaction between a planar brush and a cylindrical particle by the modified SCFT, and the influences of particle shape, particle size and grafting parameters on the interaction are discussed. In the absence of enthalpy effects, the following results are obtained: (1) At intermediate distance, a maximum appears on the force-distance curve of all the liquid brush/particle system, however, for the solid brush/particle system the presence of the maximum point relies on the parameters chosen; (2) If the particle is far away from the grafting surface, the interactions between the particle and polymer brush are similar in both cases; (3) The inflexion and maximum on the force-distance plots indicate the structural characteristics of these polymer brushes.We also study the interaction between two identical spherical brushes in a polymer melt and investigate the effects of grafting density, particle size, length of melt chains, and the mobility of the grafting sites. The results are shown as follows: (1) The structure of the spherical brushes is so susceptible to particle radius, grafting density, and the length of the melt chains that increasing these parameters will lead to a structure transition from a "wet" to "dry" brush; (2) The pairwise interactions vary from repulsive at short distance to attractive at long distance, according to different particle radius, grafting density, and the length of melt chains; (3) The attractive force between spherical brushes is a consequence of entropy increase when moving the melt chains from limited proximity of brushes to free the bulk space; (4) The differencesbetween solid and liquid brushes are unnoticeable when the two spherical brushes are not closely located. However, as the separation is decreased, the repulsion between solid brushes becomes relatively stronger than that between liquid ones.Due to the bridging role in polymer physics and nano-particle physics played by star polymers, which can be viewed as high-curvatured spherical polymer brushes, we extend our research to the interactions between regular star polymers in athermal solvents, and calculate the effective two-body interaction potential. We find the results in agreement with those of scaling theories and other particle-based simulations. For the triplet potential among three aligned bodies, the weak interaction confirms the rationality of particle-based simulations which only involve pair-wise potentials.更多还原