2008讲稿(第4章)胶体化学概述.ppt

Chapter 4 The Rheology of Dispersions 4.1 Introduction 1. What is Rheology Rheology(流变学): The study of flow and deformation of materials. Material: solid, liquid, gas, dispersions, and so on. Why? (1) Scientifically In order to understand fully the flow behavior of materials, some of the basic physical laws or rules that materials follow when subjected to external forces so that we can formulate the theories to predict the deformation and flow of matter under a given condition. （2）Engineering Materials in a colloidal state are frequently preferred in industrial processing operations. The large surface areas per unit volume of colloid enhance chemical reactivity, adsorptive capacity, heat transfer rate, and so on. (3) Technically Colloids display a wide range of rheological behavior (elastic（弹性的） like solids, viscous behavior like liquid). It becomes important to understand how the interaction forces and fluid mechanics of the dispersions affect the flow behavior of dispersions. 2. Focus on this chapter Objective(目标，任务): To discuss the flow behavior of fluids and dispersions and introduce some of the basic ideas and theories that are essential for understanding the structure and flow properties of colloids. Newton’s law of viscosity; The Einstein’s theory of viscosity of dispersions; (3) Examining some major conditions under which Einstein’s theory break down; (4) Non-Newtonian behavior of dispersions. Based on the analysis of thermodynamics(热力学) and fluid-dynamics(流体动力学) viscosity of fluid can be defined as Eq.3 shows that the rate of energy dissipation is proportional to the square of the velocity gradient, with the viscosity of the fluid as the factor of proportionality. 4.3 The Einstein’s theory of viscosity of dispersions The effect of particles on the viscosity of dispersions The presence of a colloidal size particle in the liquid increases the viscosity because of the effect it has on the flow pattern. The viscosity is depend on the con