Structural Order in Cellulose Thin Films Prepared from a Trimethylsilyl Precursor

Area of Science:

• Materials Science
• Polymer Science
• Crystallography

Background:

• Biopolymer cellulose is a key material in various applications.
• Understanding the crystallographic order in cellulose thin films is crucial for controlling material properties.
• Previous studies have focused on bulk cellulose, with less known about thin film structures.

Purpose of the Study:

• To investigate the crystallographic order and molecular orientation in cellulose thin films.
• To analyze the structural characteristics of cellulose thin films prepared via spin-coating and HCl vapor treatment.
• To compare the observed structures with known crystalline cellulose phases.

Main Methods:

• Spin-coating of trimethylsilyl cellulose precursor followed by HCl vapor treatment.
• Pre-characterization using infrared spectroscopy and atomic force microscopy.
• Grazing incidence X-ray diffraction (GIXRD) using synchrotron radiation for structural analysis.

Main Results:

• Broad diffraction peaks indicate short correlation lengths (few nanometers) in molecular packing.
• Observed patterns are comparable to cellulose phases II and III.
• Dominant film fraction shows layers oriented parallel to the substrate, leading to 1D crystallographic order with interlayer distances of 7.3 or 4.2 Å.
• Polymer chains are aligned parallel to the substrate in either edge-on or flat-on orientations.
• A minor fraction of randomly distributed cellulose nanocrystals exhibit lower packing density than known crystalline phases.

Conclusions:

• Cellulose thin films display limited, predominantly one-dimensional crystallographic order.
• Two preferred orientations (edge-on and flat-on) of polymer chains parallel to the substrate are observed.
• The structural characteristics differ from bulk crystalline cellulose, particularly in molecular packing density.