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    Observation of Surface Ordering of Alkyl Side Chains in Polystyrene/Polyelectrolytes Diblock Copolymer Langmuir Films

    Year: 2001

    Journal: Langmuir 2001, 17, 4955-4961, 20111221

    Authors: K. Shin, M. H. Rafailovich,* J. Sokolov, D. M. Chang, J. K. Cox, R. B. Lennox,* A. Eisenberg, A. Gibaud, J. Huang, S. L. Hsu, S. K. Satija

    Organizations: aNSF-MRSEC, Department of Materials Science and Engineering, State University of New York at Stony Brook, New York 11794-2275, and Elwood/John Glenn High School, 478 Elwood Road, East Northport, New York 11731 bDepartment of Chemistry, McGill University, 801 Sherbrooke Street W., Montreal, Quebec, Canada H3A2K6 cFaculte des Sciences, Universite du Maine, 72017 Le Mans Cedex, France dDepartment of Polymer Science and Engineering, University of Massachusetts, Amherst, Massachusetts dNational Institute of Standards and Technology, Gaithersburg, Maryland 20899-8562

    Block polyelectrolytes P(Sx-b-VP/RXy) composed of polystyrene (PS) blocks (x = 200, 260) and alkylated (R = Cn) poly(vinylpyridine) (PVP) (X = I or Br; y = 119-270; n = 4, 10, and 18) have been studied using the Langmuir film balance technique and in situ X-ray and neutron reflectivity measurements. Previous studies showed that the self-assembled surface micelles (with PS core and RPV+PX- corona) at the air/water interface revealed a characteristic transition (when n > 6) without any significant hydration or the submersion of the corona chains. Combined X-ray and neutron reflectivity studies of P(Sx-b-VP/RXy) polyelectrolytes show that although the polyelectrolyte block is water soluble, it remains adsorbed to the water surface. The thickness of the adsorbed layer measured by X-ray reflectivity is in agreement with that measured using neutron reflectivity. This agreement indicates that the counterions are closely associated with the alkylated PVP chains, localized at the air/water interface, and are not distributed into the subphase. Reduction of the water subphase surface tension (using 1-5 vol % n-butanol) yields no change in the two-dimensional ordering of the surface micelles but increases the thickness of the corona layer to ca. 100 Å during film compression, indicating that the alkylated blocks become submerged into the subphase under these conditions. In situ Fourier transform infrared spectroscopy performed at the air/water interface establishes that for n = 10 and 18, the alkyl chains adopt an ordered, all-trans state. However, no ordering is observed for n = 4. These results clearly indicate that transition observed in the π-Aisotherms is related to an order-disorder process.