Suspension Concentrates: Preparation, Stability and Industrial Applications

Description

Suspension Concentrates is a survey into the theory of the formulation and stabilization of suspensions, elaborating on the breaking of aggregates and agglomerates and the role of dispersing agents on flocculation and electrostatic and steric stabilization. Practical analysis by rheology is discussed. Suspension Concentrates is ideal for research scientists and Ph.D. students investigating chemistry, chemical engineering and colloidal science. A concise and accessible text on the processes of suspension formation and stability A practical approach to rheology and the use of suspensions in industrial applications The author is a well-known, respected expert on suspensions Preface Contents 1. General introduction 2. Preparation of suspension concentrates by the bottom-up process 2.1 Introduction 2.2 Preparation of suspensions by precipitation 2.2.1 Nucleation and growth 2.2.2 Precipitation kinetics 2.2.3 Seeded nucleation and growth 2.2.4 Surface modification 2.2.5 Other methods for preparation of suspensions by the bottom-up process 2.3 Characterization of suspension particles 2.3.1 Visual observations 2.3.2 Optical microscopy 2.3.3 Electron microscopy 2.3.4 Confocal laser scanning microscopy (CLSM) 2.3.5 Scanning probe microscopy (SPM) 2.3.6 Scanning tunnelling microscopy (STM) 2.3.7 Atomic force microscopy (AFM) 2.3.8 Scattering techniques 2.4 Measurement of charge and zeta potential 3. Preparation of suspensions using the top-down process 3.1 Wetting of the bulk powder 3.2 Breaking of aggregates and agglomerates into individual units 3.3 Wet milling or comminution 3.4 Stabilization of the suspension during dispersion and milling and the resulting nanosuspension 3.5 Prevention of Ostwald ripening (crystal growth) 4. Electrostatic stabilization of suspensions 4.1 Introduction 4.2 Structure of the solid/liquid interface 4.2.1 Origin of charge on surfaces 4.2.2 Specific adsorption of ions 4.3 Structure of the electrical double layer 4.3.1 Diffuse double layer (Gouy and Chapman) 4.3.2 Stern–Grahame model of the double layer 4.4 Electrical double layer repulsion 4.5 Van der Waals Attraction 4.6 Total energy of interaction 4.6.1 Deryaguin–Landau–Verwey–Overbeek (DLVO) theory 4.7 Criteria for stabilization of suspensions with double layer interaction 5. Steric stabilization of suspensions 5.1 Introduction 5.2 Adsorption and orientation of nonionic surfactants at the solid/liquid interface 5.3 Polymeric surfactant adsorption 5.4 Interaction between particles containing adsorbed surfactant layers 6. Flocculation of suspensions 6.1 Introduction 6.2 Kinetics of flocculation of electrostatically stabilized suspensions 6.2.1 Diffusion limited aggregation (fast flocculation kinetics) 6.2.2 Potential limited aggregation (slow flocculation kinetics) 6.2.3 Weak (reversible) flocculation 6.2.4 Orthokinetic flocculation 6.2.5 Aggregate structure 6.3 Flocculation of sterically stabilized dispersions 6.3.1 Weak flocculation 6.3.2 Incipient flocculation 6.3.3 Depletion flocculation 6.3.4 Bridging flocculation by polymers and polyelectrolytes 7. Ostwald ripening in suspensions 7.1 Driving force for Ostwald ripening 7.2 Kinetics of Ostwald ripening 7.3 Thermodynamic theory of crystal growth 7.4 Molecular-kinetic theory of crystal growth 7.5 The influence of dislocations on crystal growth 7.6 Influence of impurities on crystal growth and habit 7.7 Polymorphic changes 7.8 Crystal growth inhibition 8. Sedimentation of suspensions and prevention of formation of dilatant sediments 8.1 Introduction 8.2 Sedimentation rate of suspensions 8.2.1 Very dilute suspensions 8.2.2 Moderately concentrated suspensions 8.2.3 Concentrated suspensions 8.2.4 Sedimentation of flocculated suspensions 8.2.5 Sedimentation in non-Newtonian fluids 8.3 Prevention of sedimentation and formation of dilatant sediments 8.3.1 Balance of the density of the disperse phase and medium 8.3.2 Reduction of particle size 8.3.3 Use of high molecular weight thickeners 8.3.4 Use of “inert” fine particles 8.3.5 Use of mixtures of polymers and finely divided particulate solids 8.3.6 Controlled flocculation (“self-structured” systems) 8.3.7 Depletion flocculation 8.3.8 Use of liquid crystalline phases 9. Rheology of suspensions 9.1 Introduction 9.2 Rheological techniques 9.2.1 Steady state measurements 9.2.2 Rheological models for analysis of flow curves 9.2.3 Time effects during flow – thixotropy and negative (or anti-) thixotropy 9.2.4 Constant stress (creep) measurements 9.2.5 Dynamic (oscillatory) measurements 9.3 Rheology of suspensions 9.3.1 Dilute suspensions (? = 0.01) – the Einstein equation 9.3.2 Moderately concentrated suspensions (0.2 > ? > 0.01) – the Bachelor equation 9.3.3 Rheology of concentrated suspensions 10. Nonaqueous suspension concentrates 10.1 Introduction 10.2 Stability of suspensions in polar media 10.3 stability of suspensions in nonpolar media 10.4 Characterization of the adsorbed polymer layer 10.5 Theory of steric stabilization 10.6 Criteria for effective steric stabilization 10.7 Settling of suspensions and preventing the formation of dilatant sediments 10.8 Examples of suspending agents that can be applied for prevention of settling in nonaqueous suspensions 10.9 Emulsification of oil-based suspensions 10.10 Mechanism of spontaneous emulsification and the role of mixed surfactant film 10.11 Polymeric surfactants for oil-based suspensions and the choice of emulsifiers 10.12 Emulsification into aqueous electrolyte solutions 10.13 Proper choice of the antisettling system 10.14 Rheological characteristics of the oil-based suspensions 11. Characterization, assessment and prediction of stability of suspensions 11.1 Introduction 11.2 Assessment of the structure of the solid/liquid interface 11.2.1 Double layer investigation 11.3 Measurement of surfactant and polymer adsorption 11.4 Assessment of sedimentation of suspensions 11.5 Assessment of flocculation and Ostwald ripening (crystal growth) 11.5.1 Optical microscopy 11.5.2 Sample preparation for optical microscopy 11.5.3 Particle size measurements using optical microscopy 11.5.4 Electron microscopy 11.5.5 Confocal laser scanning microscopy (CLSM) 11.5.6 Scanning probe microscopy (SPM) 11.5.7 Scanning tunnelling microscopy (STM) 11.5.8 Atomic force microscopy (AFM) 11.5.9 Scattering techniques 11.6 Measurement of rate of flocculation 11.7 Measurement of incipient flocculation 11.8 Measurement of crystal growth (Ostwald ripening) 11.9 Bulk properties of suspensions, equilibrium sediment volume (or height) and redispersion 11.10 Application of rheological techniques for the assessment and prediction of the physical stability of suspensions 11.10.1 Rheological techniques for prediction of sedimentation and syneresis 11.10.2 Role of thickeners 11.10.3 Assessment and prediction of flocculation using rheological techniques 11.10.4 Examples of application of rheology for assessment and prediction of flocculation 12. Application of suspensions in pharmacy 12.1 Introduction 12.2 Particle size reduction 12.3 Dispersion and stabilization of the drug suspension 12.4 Colloid stability of pharmaceutical suspensions 12.5 Prevention of Ostwald ripening (crystal growth) 12.6 Prevention of particle settling and suspension separation 12.7 Oral suspensions 12.8 Parenteral suspensions 12.9 Ophthalmic suspensions 12.10 Topical suspensions 12.11 Reconstitutable suspensions 13. Applications of suspensions in cosmetics and personal care 13.1 Introduction 13.2 Suspensions in sunscreens 13.3 Suspensions in colour cosmetics 13.4 Lipsticks and lip balms 13.5 Nail polish 13.6 Antiperspirants and deodorants 13.7 Foundations 13.8 Liquid detergents 14. Application of suspensions in paints and coatings 14.1 Introduction 14.2 The disperse particles 14.3 The dispersion medium and film formers 14.4 Deposition of particles and their adhesion to the substrate 14.5 Flow characteristics (rheology) of paints 15. Application of suspensions in agrochemicals 15.1 Introduction 15.2 Preparation of suspension concentrates and the role of surfactants/dispersing agents 15.3 Control of the physical stability of agrochemical suspension concentrates 15.4 Ostwald ripening (crystal growth) 15.5 Stability against claying or caking Index