ABSTRACT
I. Introduction ................................................................ 137 II. Interaction Energies and Forces................................ 138
A. van der Waals Interaction Energies and Forces................................................................... 140 1. Macroscopic Particle Interactions ................ 141 2. The Hamaker Constant ................................ 143 3. The Macroscopic Approach — Lifshitz
Theory ........................................................... 144 4. Retardation of van der Waals Forces ........... 144
B. Electrical Double Layer Interaction Energies and Forces............................................ 145 1. The Electrical Double Layer......................... 146 2. The Thickness of the Electrical
Double Layer................................................. 149
3. Electrical Double Layer Interactions ........... 150 4. DLVO Interactions of Colloidal
Particles......................................................... 152 C. Non-DLVO Interaction Energies and
Forces................................................................... 154 1. Hydrophobic Forces ...................................... 155 2. Hydration Forces .......................................... 156 3. Oscillatory Forces ......................................... 156 4. Structural Forces .......................................... 157 5. Steric and Electrosteric Forces .................... 158 6. Hydrodynamic Forces ................................... 159
III. Characterization of Structures .................................. 160 A. Scattering, Optical, and Settling Approaches.... 161 B. Mechanical Characterization of Structure......... 167
1. Rheological Behavior and Rheological Parameters ................................ 168
2. Suspension Rheology and Particle Interaction....................................... 173
3. Compressive flow .......................................... 176 C. Interaction Forces on Individual particles......... 177
IV. Structure Formation and Control Through Interfacial Chemistry ................................................. 180 A. Introduction......................................................... 180 B. Coagulation ......................................................... 183
1. Hydrolyzable Metal Ions............................... 187 C. Structure Formation Due to Polymer
Action (Flocculation) ........................................... 192 1 Bridging Flocculation .................................... 194 2. Charge Neutralization .................................. 194 3. Electrostatic Patch Mechanism.................... 195 4. Depletion Flocculation .................................. 195
D. Flocculation ......................................................... 198 1. Synergistic Effect of Coagulants
(Metal Ions) and Flocculants........................ 200 2. Influence of pH and Temperature ................ 205 3. Effect of pH on Dewatering Behavior .......... 206 4. Effect of Temperature on
Dispersion Behavior...................................... 207 References............................................................................ 210
I. INTRODUCTION
Dispersed systems form a major part of our natural and engineering environment and are frequently encountered in many industrial processes (e.g., crystallization, flotation, coagulation, and flocculation) and materials involving solidfluid systems (aerosol, emulsions, paints, cosmetics, detergents, etc.). The dispersion may comprise colloidal size (largest dimension <3mm) particulate matter (dispersed phase) such as a solid, liquid, or gas surrounded by a continuous medium (dispersion phase) in a fluid, liquid, or gas. Different classes of dispersions may arise depending upon the selection of the dispersed and dispersion phases. A sol is a dispersion of a solid in a liquid while an aerosol is a dispersion of a liquid or a solid in a gas. Suspensions and pastes are examples of solid sols. Other common dispersions are solid-gas (solid aerosols), liquid-gas (liquid aerosol), liquid-liquid (emulsions) and gasliquid (foam).
