Chapter List

1 Introduction

In a famous lecture series on colloids delivered at the Massachusetts Institute of Technology,1 Overbeek discussed the properties of lyophilic and lyophobic colloids. Lyophobic or 'solvent-fearing' colloids are thermodynamically unstable, but are kinetically stable because of a high energy barrier that prevents flocculation in an energy minimum. The classical example is the so-called DLVO colloid or charge-stabilized colloid, where the kinetic stability derives from a strong electrostatic repulsion.2 Destroying the repulsion, by adding salt, makes the particles flocculate. Lyophilic or 'solvent-loving' colloids are thermodynamically stable. Unlike lyophobic colloids, they form or redisperse spontaneously. Examples are microemulsions, soap micelles and many colloids stabilized with a steric (or polymeric) layer on the surface. In food products we would call casein micelles from milk a typical example of a lyophilic colloid. The solvency of the colloid derives from a free energy gain in 'dissolving' the steric stabilizing polymer in the solvent. Thus, the continuous phase must be a good solvent for the polymer chains. A clear example here is the case of silica particles (radius 10 1000 nm), which can be stabilized with octadecyl chains (C18) grafted to their surface.3 In a good solvent such as cyclohexane, these particles redisperse spontaneously after drying, for instance. In...