Deposition of Cellulose-Based Thin Films on Flexible Substrates

Abstract

This study investigates flexible (polyamide 6.6 PA-6.6, polyethylene terephthalate PET, Cu, Al, and Ni foils) and, for comparison, stiff substrates (silicon wafers and glass) differing in, for example, in surface free energy and surface roughness and their ability to host cellulose-based thin films. Trimethylsilyl cellulose (TMSC), a hydrophobic acid-labile cellulose derivative, was deposited on these substrates and subjected to spin coating. For all the synthetic polymer and metal substrates, rather homogenous films were obtained, where the thickness and the roughness of the films correlated with the substrate roughness and its surface free energy. A particular case was the TMSC layer on the copper foil, which exhibited superhydrophobicity caused by the microstructuring of the copper substrate. After the investigation of TMSC film formation, the conversion to cellulose using acidic vapors of HCl was attempted. While for the polymer foils, as well as for glass and silicon, rather homogenous and smooth cellulose films were obtained, for the metal foils, there is a competing reaction between the formation of metal chlorides and the generation of cellulose. We observed particles corresponding to the metal chlorides, while we could not detect any cellulose thin films after HCl treatment of the metal foils as proven by cross-section imaging using scanning electron microscopy (SEM).

The Interaction of Cellulose Thin Films With Small Organic Molecules—Comparability of Two Inherently Different Methods

“…As one would expect, this is changed to a much more hydrophilic surface, with a contact angle of around 50 °, when surface regeneration is performed. Both contact angles are well in line with values reported for TMSC and regenerated cellulose in the literature (Schlemmer et al, 2018). The 60-min regenerated cellulose film sized with ASA features again a very high contact angle of 106 °.…”

Structural Order in Cellulose Thin Films Prepared from a Trimethylsilyl Precursor

“…Homogenous film thicknesses and conformational coating of the substrates are observed. 44 These films show an average mass density of 1.39 g/cm 3 , which is much smaller than the crystalline density of the known phases (1.55−1.64 g/cm 3 ). 45 The packing of the molecules has previously been considered as amorphous in very thin films.…”

“…In this work, we use TMSC as a precursor that generates individual cellulose molecules after the regeneration procedure. Homogenous film thicknesses and conformational coating of the substrates are observed . These films show an average mass density of 1.39 g/cm 3 , which is much smaller than the crystalline density of the known phases (1.55–1.64 g/cm 3 ) .…”

Micro Fibrillated Cellulose (MFC) Films on Metal Surfaces as a Substrate for Temperature Programmed Desorption (TPD) Experiments

“…For comparison a bleached unsized paper measured under the same conditions used here shows a contact angle of about 38° [12]. A regenerated thin cellulose film shows a contact angle of about 40° [15]. Figure 1 clearly shows that there are optically homogeneous dry films attached onto the stainless steel samples.…”