The use of block copolymer stabilizers for controlling dispersion stability T. COSGROVE School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, UK Received 1 May 1997 Keywords: block copolymers; emulsions; colloid stability; neutron scattering Synopsis The role of block copolymers in stabilizing colloidal dispersions against flocculation or coalescence is discussed in terms of the detailed structure of the interface. Both particulate dispersions and liquid/liquid interfaces are used as examples. Two novel experimental methods are introduced, small-angle neutron scattering and neutron reflection. Comparison with the Scheutjens Fleer theory for block copolymers is also presented. Strategies for the optimum design of the stabilizing polymer are introduced. R´ esum´ e Le rˆ ole de copolym` eres blocs dans la stabilisation de dispersions collo¨ ıdales contre la flocculation ou la coalescence est comment´ e en fonction de la structure pre´ cise de l’interface. On utilise comme exemples ` a la fois des dispersions particulaires et des interfaces liquide/liquide. Deux nouvelles m´ ethodes exp´ erimentales sont introduites, la diffusion de neutrons ` a angle faible et la r´ eflexion de neutrons. On pr´ esente aussi une comparaison avec la th´ eorie des copolym` eres blocs de Scheutjens Fleer. On introduit des orientations strat´ egiques pour la conception optimale du polym` ere stabilisateur. Introduction The stability of colloid particles in water is determined by a balance between attractive van der Waals forces and electrostatic repulsion [1]. For spherical particles of radius a, separated by a distance h in a vacuum, the van der Waals force for the case when h  2a is given by V A (h) =- Aa 12h (1) where A is the Hamaker constant that depends on the optical properties of the particle. For polystyrene latex, A has a value of 6.5  10 20 J. In a medium, rather than a vacuum, an ‘effective’ Hamaker constant, which is the geometric mean of the two phases, must be used. For example A water = 3.7  10 20 J so the effective value for a latex in water is given by (A 0.5 water - A 0.5 latex ) 2 = 0.39  10 20 J. For a polymer colloid, the electrostatic interaction is often a result of surface charge originating from an initiator, for example a polystyrene latex particle may be covered by sulphonic acid groups leading to a surface charge of several C cm -2 . For a small overlap of the potentials between two particles the repulsive interaction is given by V R = 2ea 2 d exp(-h) (2) 0142–5463 © 1997 International Journal of Cosmetic Science International Journal of Cosmetic Science 19, 157–166 (1997)