Stability of diblock copolymer/layered silicate nanocomposite thin films

The stability of thin film nanocomposites on silicon substrates, formed fro m mixtures of a symmetric diblock copolymer blended with layered silicate n anocomposites, was investigated using a combination of optical microscopy, atomic force microscopy (AFM), and X-ray diffraction (XRD). Two cases exami ned are polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) blended with mo ntmorillonite, modified with stoichiometric amounts of alkylammonium surfac tant chains, OLS(S), and PS-b-PMMA blended with montmorillonite, modified w ith excess alkylammonium, OLS(E). While the phase behavior of the OLS(S)/co polymer is similar to that observed in bulk studies, that bf the OLS(E)/cop olymer system is different. We show that an exchange occurs between surfact ant molecules in the OLS(E) system with copolymer chains and that the surfa ctant molecules form a separate layer on the substrate, resulting in a dest abilization of the film.