Study of the colloidal stability of an amphoteric latex

Undoubtedly, the DLVO theory has been and it is still very useful for explaining the stability of colloidal dispersions. This theory was independently developed by Derjaguin and Landau [1] and by Verwey and Overbeek [2] in the forties. According to this theory, the total interaction potential (VT) between two colloidal particles is the sum of the repulsive electrostatic interaction energy (VE) and the attractive London)van der Waals (dispersion) energy (VA). The total interaction energy as a function of the distance between the particles presents a minimum (the primary minimum) close to a maximum at small separations. The maximum represents the energy barrier (Vmax) opposing coagulation. If particles approach each other with sufficient kinetic energies to overcome Vmax, coagulation will occur in the primary minimum and the suspension will be destabilized. It is possible that a second minimum appears at larger separations as well. The Vmax value depends on the surface electric potential of the particles, electrolyte concentration in the medium, valence of the counterions, particle size and Hamaker constant. In particular, an increase in the electrolyte concentration causes a decrease in Vmax because the ions diminish the repulsive electrostatic interactions between the particles. Thus, there will be an electrolyte concentration (the so-called critical coagulation concentration, c.c.c.) at which the energy barrier vanishes (Vmax=0). The colloidal dispersion is then completely J.J. Valle-Delgado J.A. Molina-Bolı́var F. Galisteo-González M.J. Gálvez-Ruiz Study of the colloidal stability of an amphoteric latex