system [177]. In an intercalated composite, the clay sheets are separated at a fixed
separation such that few free polymer chains can penetrate between the sheets. While
in an exfoliated composite, the clay sheets are effectively separated from each other
and well dispersed in the free polymer matrix.
Traditionally, colloidal dispersions are stabilized by grafting polymer chains on
the surface of colloidal particles [178, 179, 180]. In case of colloids in solution, if
the repulsive barrier due to the steric hindrance of the grafted polymer chains com-
pensates the attractive minimum due to the van der Waals interactions between
the colloid particles, then the particles do not aggregate. However, the situation is
more complex for polymer-colloid mixtures. Depending on the quality of the solvent,
grafting density, and the degree of polymerization of the grafted and free polymers,
the inter-colloid interactions can become attractive destabilizing the colloidal disper-
sion. [181, 182, 183, 152].
Similar scenario occurs in polymeric alloys where the constituent homopolymers
are Compatibilized by diblock copolymers [184, 185]. The copolymer molecules act as
amphiphiles forming thin monolayers between the immiscible homopolymer domains,
preventing them from macrophase separation. Hence, block copolymers help produce
a stable blend in which the homopolymer domains do not coarsen [186, 187, 188].
The stability of the blend depends upon the effective interactions between the copoly-
mer monolayers in the presence of the homopolymers [189, 190]. It has been found
that when the homopolymer molecules are large relative to the copolymer molecules,
144
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