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Structural Order in Cellulose Thin Films Prepared from a Trimethylsilyl Precursor
journal contribution
posted on 2019-12-12, 15:35 authored by Andrew
O. F. Jones, Roland Resel, Benedikt Schrode, Eduardo Machado-Charry, Christian Röthel, Birgit Kunert, Ingo Salzmann, Eero Kontturi, David Reishofer, Stefan SpirkBiopolymer cellulose is investigated in terms of the
crystallographic
order within thin films. The films were prepared by spin-coating of
a trimethylsilyl cellulose precursor followed by an exposure to HCl
vapors; two different source materials were used. Careful precharacterization
of the films was performed by infrared spectroscopy and atomic force
microscopy. Subsequently, the films were investigated by grazing incidence
X-ray diffraction using synchrotron radiation. The results showed
broad diffraction peaks, indicating a rather short correlation length
of the molecular packing in the range of a few nanometers. The analysis
of the diffraction patterns was based on the known structures of crystalline
cellulose, as the observed peak pattern was comparable to cellulose
phase II and phase III. The dominant fraction of the film is formed
by two different types of layers, which are oriented parallel to the
substrate surface. The stacking of the layers results in a one-dimensional
crystallographic order with a defined interlayer distance of either
7.3 or 4.2 Å. As a consequence, two different preferred orientations
of the polymer chains are observed. In both cases, polymer chain axes
are aligned parallel to the substrate surface, and the orientation
of the cellulose molecules are concluded to be either edge-on or flat-on.
A minor fraction of the cellulose molecules form nanocrystals that
are randomly distributed within the films. In this case, the molecular
packing density was found to be smaller in comparison to the known
crystalline phases of cellulose.