Contents. Preface XIII

Transcription

1 V Contents Preface XIII 1 General Introduction Fundamental Knowledge Required for Successful Dispersion of Powders into Liquids Wetting of Powder into Liquid Breaking of Aggregates and Agglomerates into Individual Units Wet Milling or Comminution Stabilization of the Resulting Dispersion Prevention of Ostwald Ripening (Crystal Growth) Prevention of Sedimentation and Formation of Compact Sediments (Clays) Particle Dimensions in Suspensions Concentration Range of Suspensions Outline of the Book 12 References 16 2 Fundamentals of Wetting and Spreading Introduction The Concept of the Contact Angle The Contact Angle Wetting Line Three-Phase Line (Solid/Liquid/Vapor) Thermodynamic Treatment Young s Equation Adhesion Tension Work of Adhesion W a Work of Cohesion Calculation of Surface Tension and Contact Angle Good and Girifalco Approach Fowkes Treatment The Spreading of Liquids on Surfaces The Spreading Coefficient S Contact Angle Hysteresis 26

2 VI Contents Reasons for Hysteresis Wenzel s Equation 28 References 29 3 The Critical Surface Tension of Wetting and the Role of Surfactants in Powder Wetting The Critical Surface Tension of Wetting Theoretical Basis of the Critical Surface Tension Effect of Surfactant Adsorption Dynamic Processes of Adsorption and Wetting General Theory of Adsorption Kinetics Adsorption Kinetics from Micellar Solutions Experimental Techniques for Studying Adsorption Kinetics The Drop Volume Technique Maximum Bubble Pressure Technique Wetting of Powders by Liquids Rate of Penetration of Liquids: The Rideal Washburn Equation Measurement of Contact Angles of Liquids and Surfactant Solutions on Powders Assessment of Wettability of Powders Sinking Time, Submersion, or Immersion Test List of Wetting Agents for Hydrophobic Solids in Water 45 References 46 4 Structure of the Solid Liquid Interface and Electrostatic Stabilization Structure of the Solid Liquid Interface Origin of Charge on Surfaces Surface Ions Isomorphic Substitution Structure of the Electrical Double Layer Diffuse Double Layer (Gouy and Chapman) Stern Grahame Model of the Double Layer Distinction between Specific and Nonspecific Adsorbed Ions Electrical Double-Layer Repulsion van der Waals Attraction Total Energy of Interaction Deryaguin Landau Verwey Overbeek Theory Flocculation of Suspensions Criteria for Stabilization of Dispersions with Double-Layer Interaction 62 References 62 5 Electrokinetic Phenomena and Zeta Potential Stern Grahame Model of the Double Layer 67

3 5.2 Calculation of Zeta Potential from Particle Mobility von Smoluchowski (Classical) Treatment The Huckel Equation Henry s Treatment Measurement of Electrophoretic Mobility and Zeta Potential Ultramicroscopic Technique (Microelectrophoresis) Laser Velocimetry Technique Electroacoustic Methods 78 References 83 6 General Classification of Dispersing Agents and Adsorption of Surfactants at the Solid/Liquid Interface Classification of Dispersing Agents Surfactants Anionic Surfactants Cationic Surfactants Amphoteric (Zwitterionic) Surfactants Nonionic Surfactants Alcohol Ethoxylates Alkyl Phenol Ethoxylates Fatty Acid Ethoxylates Sorbitan Esters and Their Ethoxylated Derivatives (Spans and Tweens) Ethoxylated Fats and Oils Amine Ethoxylates Polymeric Surfactants Polyelectrolytes Adsorption of Surfactants at the Solid Liquid Interface Adsorption of Ionic Surfactants on Hydrophobic Surfaces Adsorption of Ionic Surfactants on Polar Surfaces Adsorption of Nonionic Surfactants Theoretical Treatment of Surfactant Adsorption Examples of Typical Adsorption Isotherms of Model Nonionic Surfactants on Hydrophobic Solids 103 References Adsorption and Conformation of Polymeric Surfactants at the Solid Liquid Interface Theories of Polymer Adsorption Experimental Techniques for Studying Polymeric Surfactant Adsorption Measurement of the Adsorption Isotherm Measurement of the Fraction of Segments p Determination of the Segment Density Distribution ρ(z) and Adsorbed Layer Thickness δ h 119 Contents VII

4 VIII Contents 7.6 Examples of the Adsorption Isotherms of Nonionic Polymeric Surfactants Adsorbed Layer Thickness Results Kinetics of Polymer Adsorption 128 References Stabilization and Destabilization of Suspensions Using Polymeric Surfactants and the Theory of Steric Stabilization Introduction Interaction between Particles Containing Adsorbed Polymeric Surfactant Layers (Steric Stabilization) Mixing Interaction G mix Elastic Interaction G el Total Energy of Interaction Criteria for Effective Steric Stabilization Flocculation of Sterically Stabilized Dispersions Weak Flocculation Incipient Flocculation Depletion Flocculation Bridging Flocculation by Polymers and Polyelectrolytes Examples for Suspension Stabilization Using Polymeric Surfactants Polymeric Surfactants for Stabilization of Preformed Latex Dispersions 146 References Properties of Concentrated Suspensions Interparticle Interactions and Their Combination Hard-Sphere Interaction Soft or Electrostatic Interaction: Figure 9.1b Steric Interaction: Figure 9.1c van der Waals Attraction: Figure 9.1d Combination of Interaction Forces Definition of Dilute, Concentrated, and Solid Suspensions States of Suspension on Standing 164 References Sedimentation of Suspensions and Prevention of Formation of Dilatant Sediments Sedimentation Rate of Suspensions Prevention of Sedimentation and Formation of Dilatant Sediments Balance of the Density of the Disperse Phase and Medium 178

5 Contents IX Reduction of the Particle Size Use of High Molecular Weight Thickeners Use of Inert Fine Particles Use of Mixtures of Polymers and Finely Divided Particulate Solids Controlled Flocculation ( Self-Structured Systems) Depletion Flocculation Use of Liquid Crystalline Phases 190 References Characterization of Suspensions and Assessment of Their Stability Introduction Assessment of the Structure of the Solid/Liquid Interface Double-Layer Investigation Analytical Determination of Surface Charge Electrokinetic and Zeta Potential Measurements Measurement of Surfactant and Polymer Adsorption Assessment of Sedimentation of Suspensions Assessment of Flocculation and Ostwald Ripening (Crystal Growth) Optical Microscopy Sample Preparation for Optical Microscopy Particle Size Measurements Using Optical Microscopy Electron Microscopy Transmission Electron Microscopy (TEM) Scanning Electron Microscopy (SEM) Confocal Laser Scanning Microscopy (CLSM) Scanning Probe Microscopy (SPM) Scanning Tunneling Microscopy (STM) Atomic Force Microscopy (AFM) Scattering Techniques Light Scattering Techniques Time-Average Light Scattering Turbidity Measurements Light Diffraction Techniques Dynamic Light Scattering Photon Correlation Spectroscopy (PCS) Backscattering Techniques Measurement of Rate of Flocculation Measurement of Incipient Flocculation Measurement of Crystal Growth (Ostwald Ripening) Bulk Properties of Suspensions: Equilibrium Sediment Volume (or Height) and Redispersion 216 References 217

6 X Contents 12 Rheological Techniques for Assessment of Stability of Suspensions Introduction Steady-State Shear Stress σ Shear Rate γ Measurements Constant Stress (Creep) Measurements Dynamic (Oscillatory) Measurements Steady-State Measurements Rheological Models for Analysis of Flow Curves Newtonian Systems Bingham Plastic Systems Pseudoplastic (Shear Thinning) System Dilatant (Shear Thickening) System Herschel Bulkley General Model The Casson Model The Cross Equation Time Effects during Flow Thixotropy and Negative (or anti-) Thixotropy Constant Stress (Creep) Measurements Analysis of Creep Curves Viscous Fluid Elastic Solid Viscoelastic Response Viscoelastic Liquid Viscoelastic Solid Creep Procedure Dynamic (Oscillatory) Measurements Analysis of Oscillatory Response for a Viscoelastic System Vector Analysis of the Complex Modulus Dynamic Viscosity η Note that η η(0) as ω Strain Sweep Oscillatory Sweep The Cohesive Energy Density E c Application of Rheological Techniques for the Assessment and Prediction of the Physical Stability of Suspensions Rheological Techniques for Prediction of Sedimentation and Syneresis Role of Thickeners Assessment and Prediction of Flocculation Using Rheological Techniques Strain Sweep Measurements Oscillatory Sweep Measurements Examples of Application of Rheology for Assessment and Prediction of Flocculation 240

7 Contents XI Flocculation and Restabilization of Clays Using Cationic Surfactants Flocculation of Sterically Stabilized Dispersions 240 References Rheology of Concentrated Suspensions Introduction The Einstein Equation The Batchelor Equation Rheology of Concentrated Suspensions Rheology of Hard-Sphere Suspensions Rheology of Systems with Soft or Electrostatic Interaction Rheology of Sterically Stabilized Dispersions Rheology of Flocculated Suspensions Analysis of the Flow Curve Impulse Theory: Goodeve and Gillespie Elastic Floc Model: Hunter and Coworkers Fractal Concept for Flocculation Examples of Strongly Flocculated (Coagulated) Suspension Coagulation of Electrostatically Stabilized Suspensions by Addition of Electrolyte Strongly Flocculated Sterically Stabilized Systems Influence of the Addition of Electrolyte Influence of Increase of Temperature Models for Interpretation of Rheological Results Dublet Floc Structure Model Elastic Floc Model 268 References 270 Index 271