THEORY OF STERIC STABILIZATION OF COLLOID DISPERSIONS BY GRAFTED POLYMERS

The structure and stabilizing properties of layers of long polymer chains, grafted at one end onto the surface of colloid particles, are considered. A mean-field analytical theory describing the interaction between two colloid particles covered with densely grafted polymer chains is developed. An analytical expression for the interaction potential of colloid particles, depending on the degree of polymerization, the thermodynamic stiffness of stabilizing chains, the solvent quality and the density of grafting of the chains onto the surface, is obtained. The shape and the parameters of this potential are determined by the value of the universal parameter γ introduced, which depends on the magnitude of interparticle attraction, the total amount of grafted polymer per unit area, and relative deviation from the θ-temperature. In the case of relatively weak interparticle attraction, γ < 1, with solvencies better than or equal to that of the θ-solvent, the potential curves display a single secondary minimum and thermodynamic stability of dispersion can be attained. In the case of strong interparticle attraction, γ > 1, with good solvents, the potential curves display primary and secondary minima separated by a maximum and the stability of dispersion is kinetic in character. © 1990.