2009讲稿(第13章)-dzx.ppt

Chapter 13. Electrostatic and polymer-induced colloid stability 13.1 Introduction 1. Colloid stability Colloid stability: The ability of a dispersion to resist coagulation. Kinetic stability(动力稳定性): Evaluated（评价） by kinetics. Thermodynamic stability(热力学稳定性): Evaluated by thermodynamics. Van der Waals force: attractive and is strong at short interparticle separation. The protection against van der Waals force is usually provided in one of two ways: Electrostatic force→electrical double layer. electrostatic stability(电稳定作用)。 Polymer repulsive force: The adsorbed polymer layer on dispersed particles masks(屏蔽、对抗) the attraction force of van der Waals force. Polymer-induced stability(聚合物稳定作用) or steric stability(空间稳定作用). 2. Focus of this chapter The stability and the structure of dispersions; Structure: spatial(空间的) organization（构造、架构） of the colloidal particles. How interparticle forces influence the structure of a dispersion; How the influence of interparticle interaction energies on dispersion stability; How polymer influence the stability of dispersions. 13.2 Interparticle forces, structure and stability of dispersions To know the relation between interparticle forces and the microstructure of dispersions and the factors that determine such a relation. Interplay between interpartcle forces and structure Dominated by strong repulsion; Dominated by strong attraction; Intermediate situations. 13.3 Interaction energy curves and their dependence on the properties of the dispersion The Interaction energy curves are useful for developing quantitative measure of kinetic stability of dispersions. Such a study of stability is known as the DLVO theory (Derjaguin-Landau-Verwey-Overbeek, 1940). ΦT＝ΦR+ΦA （13-1） ΦT –Total interaction energy ΦR – Repulsion energy, ΦA -Attraction energy 第二极小值处： 较大粒子（a10-8m），发生聚沉、絮凝（flocculation） 但粒子间距较大，吸引作用不大，外界条件改变，粒子可再分开。 称为“可逆聚沉”或“临时聚沉”，体系较稳定。 第一极小值处： 较小粒子越过势垒，粒子间距离小，形成沉淀，称为“不可逆聚沉”或“永久聚沉”，体系失去稳定性