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    Amorphous Characteristics of an Ultrathin Cellulose Film

    Year: 2011

    Journal: Biomacromolecules, 2011, 12 (3), pp 770–777, 20111221

    Authors: Eero Kontturi*†, Miro Suchy†, Paavo Penttil‡, Bruno Jean§, Kari Pirkkalainen‡, Mika Torkkeli‡, and Ritva Serimaa‡

    Organizations: † Department of Forest Products Technology, School of Science and Technology, Aalto University, P.O. Box 16300, 00076 Aalto, Finland, ‡ Department of Physics, University of Helsinki, P.O. Box 64, 00014 Helsinki University, Finland, § Centre de Recherche sur les Macromolcules Vgtales (CERMAV-CNRS), BP 53, 38041 Grenoble Cedex 9, France

    Swelling behavior and rearrangements of an amorphous ultrathin cellulose film (20 nm thickness) exposed to water and subsequently dried were investigated with grazing incidence X-ray diffraction, neutron reflectivity, atomic force microscopy, and surface energy calculations obtained from contact angle measurements. The film swelled excessively in water, doubling its thickness, but shrunk back to the original thickness upon water removal. Crystallinity (or amorphousness) and morphology remained relatively unchanged after the wetting/drying cycle, but surface free energy increased considerably (ca. 15%) due to an increase in its polar component, that is, the hydrophilicity of the film, indicating that rearrangements occurred during the film’s exposure to water. Furthermore, stability of the films in aqueous NaOH solution was investigated with quartz crystal microbalance with dissipation monitoring. The films were stable at 0.0001 M NaOH but already 0.001 M NaOH partially dissolved the film. The surprising susceptibility to dissolve in dilute NaOH was hypothetically attributed to the lack of hierarchical morphology in the amorphous film.