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    Characterization of Layer-by-Layer Self-Assembled Multilayer Films of Diblock Copolymer Micelles

    Year: 2008

    Journal: Langmuir 2008, 24, 116-123, 20100827

    Authors: Sakai K †‡, Webber G.B †§, Vo C-D |, Wanless E.J. ^, Vamvakaki M. #, Bütün V. @, Armes S.P.|, Biggs S. *†

    Last authors: Simon Biggs

    Organizations: School of Process, EnVironmental and Materials Engineering, UniVersity of Leeds, Leeds LS2 9JT, United Kingdom, Department of Chemistry, Dainton Building, The UniVersity of Sheffield, Brook Hill, Sheffield S3 7HF, United Kingdom, School of EnVironmental and Life Sciences, The UniVersity of Newcastle, Callaghan, New South Wales, 2308, Australia, Department of Materials Science and Technology, UniVersity of Crete, 710 03, Heraklion, Crete, Greece, and Department of Chemistry, Eskisehir Osmangazi UniVersity, Campus of Meselik, Eskisehir 26040, Turkey

    Country: Turkey

    The in situ layer-by-layer (LbL) self-assembly of low Tg diblock copolymer micelles onto a flat silica substrate is reported. The copolymers used here were a cationic poly(2-(dimethylamino)ethyl methacrylate)-block-poly(2-(diethylamino)ethyl methacrylate) (50qPDMA-PDEA; 50q refers to a mean degree of quaternization of 50 mol % for the PDMA block) and zwitterionic poly(methacrylic acid)-block-poly(2-(diethylamino)ethyl methacrylate) (PMAAPDEA), which has anionic character at pH 9. Alternate deposition of micelles formed by these two copolymers onto a silica substrate at pH 9 was examined. The in situ LbL buildup of the copolymer micelle films was monitored using ú potential measurements, optical reflectometry, and a quartz crystal microbalance with dissipation monitoring (QCMD). For a six layer deposition, complete charge reversal was observed after the addition of each layer. The OR data indicated clearly an increase in adsorbed mass with each additional micelle layer and suggest that some interdiffusion of copolymer chains between layers and/or an increase in the film roughness, and hence in the effective surface area of the micellar multilayers, must take place as the film is built up. QCM-D data indicated that the self-assembled micellar multilayers on a flat silica substrate undergo structural changes over a prolonged period. This is attributed to longer-term interdiffusion of the copolymer chains between the outer two layers after the initial adsorption of each layer is complete. The QCM-D data further suggest that the outer adsorbed layers adopt a progressively more extended conformation, particularly for the higher numbered layers. The morphology of each successive layer was characterized using in situ soft-contact atomic force microscopy, and micelle-like surface aggregates are clearly observed within each layer of the complex film, suggesting the persistence of aggregate structures throughout the multilayer structure.