Humidity Response of Cellulose Thin Films

Area of Science:

• Materials Science
• Biochemistry
• Physical Chemistry

Background:

• Cellulose-water interactions are vital for biological systems and the creation of advanced cellulose-based materials.
• Studying these interactions is challenging due to the inherent variability of natural cellulose fibers and structural modifications.
• Well-defined, ultrathin cellulose films offer a controlled model system to investigate humidity responses.

Purpose of the Study:

• To investigate the humidity response of ultrathin cellulose films subjected to industrially relevant treatments.
• To quantify the impact of drying, swelling, and combined treatments on water incorporation into cellulose.
• To elucidate the structural changes occurring in cellulose films upon water interaction.

Main Methods:

• Preparation of ultrathin cellulose films via spin coating of a soluble derivative followed by conversion.
• Real-time monitoring of film thickness, roughness, and electron density using X-ray reflectivity (XRR) and Quartz Crystal Microbalance with Dissipation (QCM-D).
• Qualitative analysis of structural alterations using Grazing Incidence Small Angle X-ray Scattering (GISAXS) with synchrotron radiation.

Main Results:

• At 97% relative humidity, cellulose films incorporated 3.6 water molecules per anhydroglucose unit (AGU), irrespective of the cellulose source.
• Industrial treatments, particularly drying at elevated temperatures, significantly reduced water uptake (to 2.0 and 2.6 molecules per AGU).
• XRR and QCM-D provided real-time data on film swelling and water incorporation, while GISAXS offered insights into structural changes.

Conclusions:

• The water uptake capacity of cellulose films is highly sensitive to pre-treatment conditions, especially drying.
• Ultrathin cellulose films provide a robust platform for studying fundamental cellulose-water interactions and the effects of processing.
• Understanding these structure-property relationships is crucial for optimizing cellulose-based materials for specific applications.