Basic Principles of Formulation Types

Tharwat F. Tadros

• Publisher: De Gruyter
• Year: 2018
• eBook ISBN: 9783110587579
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Chemistry
• Index: Chemistry

Volume 2 of Formulation Science and Technology is a survey of the different types of formulations used in the chemical industry and offers numerous real-world examples of foams, gels, latexes etc. It offers in-depth explanations for research scientists, universities, and industry practitioners looking for a complete understanding of which type formulation works best for a certain application and why.

1Formulation of solid/liquid dispersions (suspensions)

1.1Introduction

Many chemicals are formulated as solid/liquid dispersions (to be referred to as suspensions), e.g. paints, dyestuffs, paper coatings, printing inks, agrochemicals, pharmaceuticals, cosmetics, food products, detergents, ceramics, etc. The powder particles can be hydrophobic, e.g. organic pigments, agrochemicals, ceramics or hydrophilic, e.g. silica, titania, clays [1–5]. The liquid can be aqueous or nonaqueous. The average particle size of the suspension can be within the colloid range (1 nm–1 μm) or outside the colloid range (> 1 μm). Suspensions with dimension within the colloid range are referred to as colloidal suspensions. In contrast, suspensions with dimensions outside the colloid range are generally referred to as coarse suspensions. They are to be distinguished from colloidal suspensions in the sense that the particles of coarse suspensions settle to the bottom of the container (as a result of the gravitational field on the particles) whereas with colloidal suspensions, with particle density not significantly larger than that of the medium, the very mild mixing produced by ambient thermal fluctuations and/or Brownian motion can keep the particles uniformly dispersed in the continuous medium [1]. The formulation of suspensions and maintenance of their physical stability over long periods of time under various conditions, e.g. temperature variation, transport, etc. still remains a challenging problem to the formulation scientist or chemical engineer. This requires understanding of the various interfacial phenomena involved in their preparation and stabilization [6, 7].

The concentration of a suspension is described by its volume fraction ϕ, namely the ratio between the total volume of particles to the volume of the suspension. The value of ϕ above which a suspension may be considered “dilute”, “concentrated” or “solid” can be defined from a consideration of the balance between the particle translational motion (Brownian diffusion) and interparticle interaction [2, 8]. If Brownian diffusion predominates over the imposed interparticle interaction, the suspension may be described as “dilute”. In this case the particle translational motion is large and only occasional contacts may occur between the particles which are then separated by the Brownian force. The particle interactions can be represented by two-body collisions. This “dilute” suspension has generally time-independent properties and if the particle size is within the colloid range and the density difference between the particles is very small, no gravitational sedimentation of particles occurs and the system maintains its properties over long periods of time. These “dilute” suspensions show Newtonian flow, i.e. their viscosity is independent of the applied shear rate [9]. In contrast, if interparticle interaction predominates over Brownian diffusion, i.e. the interparticle distance h becomes much smaller than the particle radius, the system may be described as a “solid” suspension. In this case the particles may vibrate with a distance h that is much smaller than the particle radius. The interaction produces a specific order between the particles and a highly developed structure is reached. The resulting “solid” suspension becomes predominantly elastic with very little energy dissipation during flow [9]. Again, the properties of these elastic systems are time-independent. In between the two extremes one ma...

Table of contents

• Cover
• Title Page
• Copyright
• Preface
• Contents
• 1 Formulation of solid/liquid dispersions (suspensions)
• 2 Formulation of liquid/liquid dispersions (emulsions)
• 3 Formulation of foams
• 4 Formulation of gels
• 5 Formulation of polymer colloids (latexes)
• 6 Formulation of microemulsions
• 7 Controlled-release formulations
• 8 Solid dosage formulations
• 9 Assessments of the stability of formulations
• Index