Determination of the distance of nearest approach of coagulated particles in haematite and latex dispersions

Previous investigations [H. Lichtenfeld, L. Knapschinsky, H. Sontag, V. Shi lov, Colloids Surfaces A: Physicochem. Eng. Aspects 104 (1995) 113; H. Lich tenfeld, H. Sonntag, C. Durr, Colloids Surfaces 54 (1991) 267] and the work presented here on the kinetics of the rapid coagulation process by means o f our single-particle light scattering photometer led to the conclusion tha t the deaggregation constants for haematite and latex suspensions are finit e values. From this finding, we can conclude that the approach of two parti cles resulting in aggregation does not lead to contact of the surfaces; it can be prevented by a structural barrier of the dispersion medium. A new wa y to determine this layer thickness is a quantitative determination of the decay of aggregates (measurement of the velocity constants of deaggregation ) together with the determination of the aggregation constants at the aggre gation proccess, which are connected to the second virial coefficient. (C) 1998 Elsevier Science B.V. All rights reserved.