Book contents
- Frontmatter
- Contents
- Preface to the third edition
- Preface to the first edition
- Preface to the second edition
- Introduction
- 1 Atoms, molecules and the forces between them
- 2 Temperature, heat and the laws of thermodynamics
- 3 Perfect gases – bulk properties and simple theory
- 4 Further theory of perfect gases
- 5 Imperfect gases
- 6 The solid state
- 7 The elastic properties of solids
- 8 The strength properties of solids
- 9 Thermal and electrical properties of solids
- 10 The liquid state
- 11 Liquids: their flow properties
- 12 The colloidal state of matter
- 13 Some physical properties of polymers
- 14 Dielectric properties of matter
- 15 Magnetic properties of matter
- Appendix: Values of some physical constants
- Index
12 - The colloidal state of matter
Published online by Cambridge University Press: 05 June 2012
- Frontmatter
- Contents
- Preface to the third edition
- Preface to the first edition
- Preface to the second edition
- Introduction
- 1 Atoms, molecules and the forces between them
- 2 Temperature, heat and the laws of thermodynamics
- 3 Perfect gases – bulk properties and simple theory
- 4 Further theory of perfect gases
- 5 Imperfect gases
- 6 The solid state
- 7 The elastic properties of solids
- 8 The strength properties of solids
- 9 Thermal and electrical properties of solids
- 10 The liquid state
- 11 Liquids: their flow properties
- 12 The colloidal state of matter
- 13 Some physical properties of polymers
- 14 Dielectric properties of matter
- 15 Magnetic properties of matter
- Appendix: Values of some physical constants
- Index
Summary
In this chapter we describe briefly some of the main features of the colloidal state. The colloidal state is very widespread in biological systems and in many practical situations. Basically a colloid consists of two distinct phases, a continuous phase (the dispersion medium) and a particulate phase, where the particles generally have dimensions ranging between 20 and 2000 Å (2 and 200 nm). The two phases can be liquidin- liquid (milk), solid-in-liquid (paint), liquid-in-gas (aerosol) and other combinations. The basic problem with colloidal systems is their stability. Clearly the particles must not be too large otherwise gravity will produce ready sedimentation. However, if the density of the two phases is similar this tendency will be reduced. The other important factor is the attractive force between the particles: if this is too large the particles will cling together and separate as a cluster from the dispersion. To prevent this, various techniques are employed to reduce the attractive forces or to introduce repulsive forces.
van der Waals forces between macroscopic bodies
Before we approach the problem of colloid stability we need to know the van der Waals forces between the particles and how these are affected by the presence of a continuous phase (e.g. a liquid) between them.
The van der Waals force between macroscopic materials was quoted in Chapter 1 (equations (1.21) and (1.22)) in order to demonstrate the difference between normal and retarded forces. Here we indicate a simple derivation.
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- Gases, Liquids and SolidsAnd Other States of Matter, pp. 312 - 331Publisher: Cambridge University PressPrint publication year: 1991