Humidity Response of Cellulose Thin Films

Abstract

Cellulose–water interactions are crucial to understand biological processes as well as to develop tailor made cellulose-based products. However, the main challenge to study these interactions is the diversity of natural cellulose fibers and alterations in their supramolecular structure. Here, we study the humidity response of different, well-defined, ultrathin cellulose films as a function of industrially relevant treatments using different techniques. As treatments, drying at elevated temperature, swelling, and swelling followed by drying at elevated temperatures were chosen. The cellulose films were prepared by spin coating a soluble cellulose derivative, trimethylsilyl cellulose, onto solid substrates followed by conversion to cellulose by HCl vapor. For the highest investigated humidity levels (97%), the layer thickness increased by ca. 40% corresponding to the incorporation of 3.6 molecules of water per anhydroglucose unit (AGU), independent of the cellulose source used. The aforementioned treatments affected this ratio significantly with drying being the most notable procedure (2.0 and 2.6 molecules per AGU). The alterations were investigated in real time with X-ray reflectivity and quartz crystal microbalance with dissipation, equipped with a humidity module to obtain information about changes in the thickness, roughness, and electron density of the films and qualitatively confirmed using grazing incidence small angle X-ray scattering measurements using synchrotron irradiation.

Biobased Nanomaterials─The Role of Interfacial Interactions for Advanced Materials

“…The reason for this at-first-unexpected result is the nanoscale porosity and, consequently, the larger surface area and higher number of hydroxyl groups accessible for water molecules in the more crystalline film. The importance of the film structure for water adsorption was also pointed out by Reishofer et al, who observed that both the preparation method and the applied treatment (e.g., drying at elevated temperature) affected the water uptake of highly amorphous cellulose thin films, especially at high relative humidities . Similarly Niinivaara et al observed that the ratio between crystalline and amorphous regions was not the only factor determining the swelling of 2D films where CNC and amorphous cellulose were combined to mimic plant cell walls .…”

“…The importance of the film structure for water adsorption was also pointed out by Reishofer et al, who observed that both the preparation method and the applied treatment (e.g., drying at elevated temperature) affected the water uptake of highly amorphous cellulose thin films, especially at high relative humidities. 78 Similarly Niinivaara et al observed that the ratio between crystalline and amorphous regions was not the only factor determining the swelling of 2D films where CNC and amorphous cellulose were combined to mimic plant cell walls. 79 In this system, the total interfacial area between CNC and amorphous cellulose was also suggested to play a role in swelling.…”

Enhancing the Performance of Triboelectric Generator: A Novel Approach Using Solid–Liquid Interface-Treated Foam and Metal Contacts

“…Thus, cellulose, which contains numerous hydroxyl groups with a strong electron donation capacity, is a high electropositivity material for triboelectrification. In addition, the hydrogen-bonded network formed due to the interaction between water molecules and the hydroxyl groups of cellulose creates a conductive path [ 35 , 36 , 37 , 38 ] that can facilitate charge transfer during the electricity generation process. The characterization of the cellulose foam is presented in Figure 1 .…”

“…When cellulose comes into contact with water, the hydroxyl groups spontaneously form hydrogen bonds with water molecules. This leads to the fixing of water molecules on the surface of cellulose and the formation of a conductive path through the hydrogen-bonded network of water molecules [ 35 , 36 , 37 , 38 ]. This property of cellulose could be an important factor to explore in solving the problem of the decreasing trend of electricity performance in high-humidity environments.…”

Enhanced water-responsive actuation of porous Bombyx mori silk

“…One common feature of high-performance WR materials developed in nature, such as cellulose- [8][9][10] and proteinbased 11,12 WR materials, is that they often consist of hierarchical and stiff architectures with pores at a nanometer scale. 2,11 For instance, a recent study showed that Bacillus subtilis cell wall peptidoglycan possesses a rigid (1.7-4.5 GPa Young's modulus) and hierarchical structure with nanoscale pores (B6.8-38.4 nm in diameter) and shows a record-high WR energy density of 72.6 MJ m À3 , surpassing those of existing actuator materials and muscles.…”