An effect of the cation-exchange capacity (CEC) on the formation of polystyrene-clay nanocomposites is reported. Two types of 2:1 layered silicates with different CECs, Wyoming (97 mequiv / 100 g of clay) and bentonite H (BNH; 131 mequiv/100 g of clay) were investigated. The organoclay was prepared through the mixing of purified clay and octaclecyldimethylammonium chloride (ODA) in an aqueous solution. The packing of the intercalated ODA surfactant depended on the CEC and the degree of solvent extraction. Two possible phases of the interlayer packing, solidlike and liquidlike, were detected for the extracted BNH because of the charge heterogeneity of the clay. The liquidlike phase showed a good affinity toward the styrene monomer, which promoted the formation of exfoliated nanocomposites. On the other hand, the solidlike phase showed a restricted dispersion in the styrene monomer. The organoclay interlayer showed limited expansion by the styrene monomer. This led to the formation of intercalated nanocomposites. An increase in the organoclay loading hindered the formation of the exfoliated nanocomposites. (C) 2004 Wiley Periodicals, Inc.