The stability of thin film nanocomposites on silicon substrates, formed from mixtures of a symmetric diblock copolymer blended with layered silicate nanocomposites, was investigated using a combination of optical microscopy, atomic force microscopy (AFM), and X-ray diffraction (XRD). Two cases examined are polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) blended with montmorillonite, modified with stoichiometric amounts of alkylammonium surfactant chains, OLS(S), and PS-b-PMMA blended with montmorillonite, modified with excess alkylammonium, OLS(E). While the phase behavior of the OLS(S)/copolymer is similar to that observed in bulk studies, that bf the OLS(E)/copolymer system is different. We show that an exchange occurs between surfactant molecules in the OLS(E) system with copolymer chains and that the surfactant molecules form a separate layer on the substrate, resulting in a destabilization of the film.