柔性界面系统中带电胶体相互作用机制的研究

It is a crucial and complex system with a hybrid of charged colloids and soft interfaces which widely used in daily life, biology field, the preparation of new function materials in industry and so on. The interactions of this system are paid extensive attention in recent years. However, the mechanism of these interactions is still not clear. In this project, the interactions of charged colloids on an organic or inorganic soft interface consist of fluid-fluid interface, biomembrane, polymer brush and so on, will be deeply investigated. The project is composed of three parts. (1)We will take the redistribution of the surface charges on the colloids as an entry point, and calculate the electrostatic interaction of the colloids confined on the interface of inorganic soft interfaces, such as fluid-fluid interfaces. From this study, we hope to make clear of the quality (attraction or repulsion) of the electrostatic interaction between like-charged colloids on the soft interafaces, wich is widely concerned in the internation.(2)The near-field electrostatic interactions of the system of charged colloids on a soft deformable membrane are studied by a combiding method with the boundary integral equation technique and multipole collaction method. In this study, Green functions will be used and various boundary conditions will be concerned.(3)The real-space self-consistent field theory (SCFT) will be developed to fit a charged colloid-polymer system. Using this developed SCFT, we will investigate the competition mechanism of the interactions of the charged colloids on polymer brush surfaces and analyse the influences of various system parameters on these interactions,such as the ion's density and valence, the sizes and distribution of surface charges of the colloids and polymer steric effect. From this investigation, we hope that it will provid a new idea or method for the stablization of the colloid solutions, the preparation of the colloid crystals, the understanding of the interactions of the biomolecules and so on.

柔性界面系统中的带电胶体体系广泛地存在于日常生活、生物领域、新材料领域等。该体系的相互作用问题是软物质物理研究的热点，但目前其作用机制的研究仍不深入。本项目将对液-液等无机柔性界面和生物膜、高分子刷等有机柔性界面上带电胶体颗粒相互作用机制作深入研究。本项目以胶体颗粒表面电荷重整化为切入点，分析液-液等无机流动界面上带电胶体的静电作用，以期理清国际上令人关注的"同性相吸或相斥"机理；联合运用边界积分法和多极子配点法，借助Green函数，充分考虑各类边界条件，对可形变光滑柔性界面上带电胶体颗粒的近场静电作用作全面计算；发展实空间自洽场动力学模型以适应带电体系，运用该模型分析高分子刷界面上带电胶体体系各类相互作用的竞争机制，分析溶液离子浓度和种类、胶体尺寸和电荷分布、高分子空间位阻效应等对体系相互作用的影响，以期为胶体体系的稳定性、胶体晶体的制备、生物体内大分子相互作用的认识等提供新的思路和指导

本项目现对液-气界面及生物膜（有机高分子刷）等柔性界面上带电胶体颗粒的有效相互作用做了详细的计算。分析了体系有效相互作用随电解质特征参数如，带电特性、聚合度等，和外在因素如溶剂性质等，及胶体分子的尺寸、带电特性等因素的变化规律, 阐明静电作用、反离子的熵效应和高分子链弹性等因素对胶体相互作用的影响机理。在对液-气界面-胶体体系的研究过程中，我们发展了一套半解析的方法来求解此体系中带电胶体颗粒的静电作用，并进一步将此方法推广到具有任意规则形状的胶体和规则形状边界的有限体系。计算结果表明，体系静电相互作用势能对胶体表面的电荷分布十分敏感，它会随着表面电荷分布的变化发生量的甚至质的变化。经过分析发现这种现象主要原因是胶体表面电荷分布的各向异性及体系界面电介常数的不对称性导致胶体附近离子云分布的不对称从而使得体系产生有效偶极矩。当两个胶体球附近电子云有效偶极矩达到一定大小且它们之间的夹角小于某个临界角度，体系将出现反常的“同性相吸”的现象。在对高分子刷体系胶体颗粒的相互作用问题的研究中，我们分别从体系静电作用、两体非静电作用、高分子的熵、溶剂熵及离子熵等几个方便入手，全面的分析了胶体分子相互作用的竞争机制。在中性体系中，在溶剂和高分子的熵与体系体积排斥作用相互竞争下，溶剂的性质对胶体的行为有着质的影响。这个现象启发我们在实验室中我们可以通过改变溶剂的亲水性使得胶体溶液在分散相和凝聚相两种状态中进行可逆转变，这将为我们的智能材料的设计提供很好的思路。当往体系中加入离子并使胶体和高分子刷带相反电荷时，胶体分子之间的有效相互作用势在不良溶剂中出现非常有意思的震荡行为，即胶体之间随着距离的增大出现“排斥-吸附-排斥-吸附”周期反复的行为。这个行为出现的主要原因是高分子-溶剂界面双电层随胶体分子距离增大周期性的变化的结果。此现象表明，带电胶体颗粒在聚电解质刷表面可能会形成多结构的自组装形式。这将为实验室带电体系的胶体自主装提供很好的思路。