  The interactions between spherical colloids covered with end-grafted polymers
(brushes) immersed in a polymer melt are studied theoretically. We show that
attractive enthalpic interactions between the two polymer species,
characterized by a negative Flory parameter (chi<0), can stabilize the
colloidal dispersion. The stabilizing mechanism is a result of a structural
change from a dry brush, where the melt chains do not penetrate deeply into the
brush, to a wet brush, where the free chains penetrate the brush and force the
grafted chains to extend into the melt.
