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1、Chapter 13. Electrostatic and polymer-induced colloid stability,13.1 Introduction 1. Colloid stabilityColloid 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
2、 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 forceelectrical double layer.electrostatic stability(电稳定作用)。 Polymer repulsive force: The adsorbed polymer layer on dispersed particles
3、 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 influenc
4、e 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 microstruc
5、ture 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.,Interparticle forces and the corresponding microstructure of monodisperse colloids,How inter
6、particle forces and the concentration of the particles to determinethe structure of dispersions.,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. S
7、uch a study of stability is known as the DLVO theory (Derjaguin-Landau-Verwey-Overbeek, 1940).TR+A （13-1）T Total interaction energy R Repulsion energy, A -Attraction energy,Boltzman constant，1/kthickness of electrical double layer 0a constant,（13-2）,（13-3）,A- Hamaker constant 与组成质点的参数有关分子间的相互作用有关 D-
8、 Distance between two particles,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。,Effect of theHamaker constant,AThe height ofthe potential energy barrier .,2. Effect of the surface potential（0）,0 The
9、 height of the potential energy barrier .,3. Effect of Electrolyte concentration,k-empirical adjustment (经验调整参数),k is quantity depends on both concentrationand valence of the indifference（不相干）electrolyte.,kThe height ofthe potential energy barrier .,电解质的聚沉作用 1. 老化与聚沉 （1）老化（Ostwald ripening） 由Kelvin公
10、式可知， 质点颗粒越小，溶度越大 老化取决于二质点的溶度差的大小和分子由小质点向大质点扩散的速度 其结果为小质点消失，大质点均匀化，个数减少,（2）聚沉 质点聚并而发生沉降 亲液、缔合、憎液胶体电解质，均会聚沉 而憎液胶体尤为敏感，主要是双电层的破坏,2. 聚沉的实验规律 （1）Schulze -Hardy规则 起聚沉作用的主要是反离子，价数越高，聚沉效率越高 反离子价数，浓度， ，稳定性 聚沉值：指定条件下使溶胶聚沉所需的电解质的最低浓度 反离子聚沉值：一价25150二价0.52三价0.010.1 聚沉值聚沉能力稳定性 此规则仅适用于不相干电解质（电离形成的离子与表面电势（0）无关，可使）。
11、,临界聚沉浓度聚沉值 电解质浓度势垒下降 溶液中电解质使势能曲线 的最高点恰为零，体系为 临界聚沉状态时的浓度离子价数越高（z），聚沉值越小，用量越少；双电层越小，排斥能减弱；介质的介电常数大，聚沉值高,（2）离子大小 一价离子感胶离子序，聚沉能力： 正离子：H+ CS+ Rb+ NH4+ K+ Na+ Li+ 负离子：F- IO3- H2PO4- BrO3- Cl- 水化半径：小大，聚沉值：小大，聚沉能力：大小 反离子水化半径增大，使静电引力减弱，不易被质点吸附。 （3）同号离子的影响 同号，大的有机离子由于质点Van der Waals力的吸引而被吸附，使，稳定性,（4）不规则聚沉大离子或
12、高价离子：少量聚沉c又分散c聚沉使变成反号重新稳定,（5）互沉现象电性相反的胶体混合发生聚沉，与其比例有关 原因：电荷相互中和电中性稳定剂相互作用，失去稳定作用 明矾净水：水中悬浮物带负电明矾水解产物Al(OH)3，带正电,13.4 Polymer-colloid mixture,Polymers(聚合物) can be used to stabilize colloid and the role of polymers on colloid stability is considerably more complicated than electrostatic stability. If
13、the added polymers are polyelectrolyte(聚电解质), then a clearly have a combination of electrostatic effect as well as effects that arise solely(单独地) from the polymeric nature of the additive. This combined effect is referred to as electrosteric stabilization（电空间稳定）.,A simplified representation of the e
14、ffects of polymers on the stability of dispersions,Bridging flocculation （桥联絮凝）,Steric stabilization （空间稳定）,Depletion flocculation （空缺絮凝作用）,Depletion stabilization （空缺稳定作用）,当胶体粒子接近到距离小于高分子在溶液中的尺寸时，粒子之间的空间内的高分子浓度将显著减小，形成所谓空缺区。 由于粒子之间的空间内与体相溶液内的高分子浓度不同而产生的渗透压，在粒子间产生了附加的吸引作用。当溶液中高分子浓度足够高时，这一吸引作用可以导致胶体絮
15、凝，这称为空缺絮凝作用。 另一方面，当粒子接近到粒子之间形成空缺区时，胶体体系必定先经历从高分子均匀分布到不均匀分布的变化。这在热力学上是一个能量升高过程，因此表现为粒子间的排斥作用。在溶液中高分子浓度很高时，这一作用足以使胶体保持稳定，这称为空缺稳定作用(depletion stabilization)。 空缺絮凝和空缺稳定作用都发生在溶液中高分子浓度很高的情形，产生空缺稳定作用所要求的高分子浓度更高。,The structure of polymer chains in bulk solution and near a solid interface,接枝,Segment (链段),Int
16、eraction between polymer-coated particles.,Overlap(重叠) of adsorbed polymer layers on closeapproach of dispersedsolid particles.,Combination of the electrostatic effects and steric stabilization.TRASSEnergy potential of steric stabilization,Effects of particles on the interface between oil drops and water is like the steric effect of polymers.,
