STERIC STABILIZATION IN WORSE THAN THETA-SOLVENTS

The stabilization of colloidal particles by nonionic polymers that exhibit loopy adsorption is considered in terms of an exponentially decaying segment density distribution function. It is shown that the steric interaction, whether repulsive or attractive, in the interpenetrational domain is drastically reduced for an exponential function, compared with that for a constant or a Gaussian distribution function. This reduction originates in the small segment densities that occur in the outer regions of steric layers exhibiting loopy adsorption. The net effect is that incipient instability in such systems can only be generated by significant penetration into the worse than 8-solvent domain. Any correlation between the critical flocculation point and the θ-point is thus weakened and stable dispersions can be prepared in worse than θ-solvents for the stabilizing chains in free solution. Both phenomena have been observed experimentally. It is predicted that, in general, the penetration into the worse than B-solvent domain will be greater for nonaqueous than for aqueous dispersion media. The conformational effects are reinforced by any changes in the thermodynamic parameters due to loopy adsorption. © 1979 Dr. Dietrich Steinkopff Verlag.