Structural Order in Cellulose Thin Films Prepared from a Trimethylsilyl Precursor

Abstract

Biopolymer cellulose is investigated in terms of the crystallographic order within thin films. The films were prepared by spincoating 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 flaton. 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.

Nanocelluloses and Related Materials Applicable in Thermal Management of Electronic Devices: A Review

“…Subsequently, NCs have appeared promising as the heat spreading materials. There are several polymorphs of crystalline cellulose (I, II and III) [42,43]. Cellulose I is the crystalline cellulose that is naturally produced by various organisms and it is often referred to as "native" or "natural" cellulose.…”

Macro- and Microstructural Evolution during Drying of Regenerated Cellulose Beads

“…introduced LiCl/DMAc as a nonderivatizing solvent for cellulose in the early 1980s and since then it has become the standard solvent for gel permeation chromatography (GPC) analysis of the molecular mass of cellulosic materials. , The mechanism of cellulose dissolution in this solvent system has been studied by using nuclear magnetic resonance (NMR), ,, and it was found that LiCl/DMAc breaks the intermolecular interactions resulting in a molecular solution of cellulose. Previous work has focused on the cellulose dissolution mechanism. , There are a few recent studies where the supramolecular rearrangements in cellulose thin films were established by grazing incidence small-angle X-ray scattering (GISAXS) measurements during the conversion of trimethylsilyl cellulose to cellulose via HCl vapor hydrolysis, , and the effect of heat treatment on its structure and morphology was established . GISAX was also employed by Roth et al .…”

Humidity Response of Cellulose Thin Films

“…This exposure cleaves off the silyl groups leaving a rather amorphous cellulose thin film with only short-range ordered cellulose molecules. 39 Since the vapor pressure of the solvent during spin coating can affect the film structure, two different TMSC derivatives featuring a different solubility behavior (CHCl 3 and THF) and molecular mass ( M w : 130 vs 120 kDa) were selected to prepare cellulose thin films. In the following, the cellulose films derived from TMSC A are denoted as Cell A whereas those from TMSC S are denoted as Cell S .…”

“…3 to 6 nm definitely influence water uptake into the films. 39 Furthermore, the different vapor pressures of the employed solvents may contribute to this effect. The necessity to induce a third layer for the description of the Cell A films, also point the distinction of the film structures between Cell A and Cell S .…”