THEORETICAL AND EXPERIMENTAL COMPARISON OF THE COLLOID STABILITY OF 2POLYSTYRENE LATEXES WITH DIFFERENT SIGN AND VALUE OF THE SURFACE-CHARGE

The purpose of this paper is to apply the classical DLVO theory to exp lain the colloid stability of two model colloids with similar size and different sign and value of the surface charge. For this comparison t he hydrodynamic interaction and the presence of hydration forces (exte nded DLVO theory) have been taken into account. The experimental stabi lity factor and the experimental doublet rate constant in diffusion co nditions were compared with those evaluated theoretically. The mathema tical treatment permits an easy evaluation and interpretation of the d ifferent adjustable parameters such as the Hamaker constant, diffuse l ayer potential and the hydration layer thickness. The theoretical and experimental comparison shows that the ''extended DLVO theory'' only p ermits to explain the stability curves Log[W]/Log[KBr] in a semiquanti tative way by using, for the evaluation of the total interaction poten tial VT: a Value of the Hamaker constant (A) similar to the classical theoretical one for polystyrene particles dispersed in water. In the c ase of the anionic latex, it was necessary to admit the presence of a hydration layer of a thickness similar to the radius of the hydrated/ dehydrated counterion. On the other hand, by using the experimental do ublet rate constant in diffusion conditions, we obtain a lower value o f the Hamaker constant (A), but within the range of the ii Values usua lly found in previous studies.