Abstract
It has been extensively reported that cellulose nanocrystals (CNCs) can represent structural colors due to their unique chiral-nematic self-assembly. However, the application of this remarkable structure does need further investigation. It has been challenging to keep the selective reflection band (SRB) resulting from the CNC structure in the visible spectrum. Herein, composition of CNC colloidal suspensions with polyethylene glycol (PEG) and glycerol (Gly) have been studied to develop humidity-responsive sensors in the form of coatings and films. The fabricated samples were characterized for their mechanical properties, optical properties, water uptake capacity, water contact angle, and surface roughness. Additionally, the chemical structure of the samples was studied with FTIR spectroscopy. The produced humidity indicators on microbial glass slides were maintained and tested in a different relative humidity range from 20% to 98% with a different color response from blue to red, respectively. The color change of the humidity sensors was reversible for several cycles. It should be noted that the color change can be detected easily by the naked eye. The water uptake test showed that pure CNC and CNC/Gly had the lowest (34%) and highest (83%) water absorption levels. The mechanical tests for CNC/PEG composites showed the highest tensile strength (40.22 MPa). Moreover, microstructural characterizations confirmed the CNC pitch formation in all the samples. Addition of the fillers increased the CNC pitch, resulting in a mesoporous film formation. These produced humidity sensors are promising candidates in food and drug packaging due to their biodegradability, biocompatibility, and cost-effectiveness.
Highlights
Accepted: 25 October 2021The importance of color in natural creatures is undeniable
Strong birefringence and colorful regions (Michel-Lévy interference color chart) [49] with random sizes and alignments were observed in the neat CNC film (Figure 3a). These domains show alignment of the CNC rods in the film that did not involve in the helix formation, which could be the result of a competition between different factors such as nematic energy, surface tensions, different evaporation rates, etc
It should be noted that these bright domains are rather randomly oriented areas that help to have more structural colorations in the matrix
Summary
The importance of color in natural creatures is undeniable. Structural colors and pigments are two common forms of color in nature. CNC films and coatings with fast response, wide range, and reversible structural colors in response to surrounding humidity, while showing good mechanical properties, which different plasticizers or a combination of several plasticizers [44] In this regard, the mixture of could open a new approach for developing biodegradable materials for functional packglycerol and polyethylene glycol (PEG). Regarding finding a better application for using CNCs as an intelligence material, we report a facile method to provide stimuli-responsive chiral nematic CNC films and coatings with fast response, wide range, and reversible structural colors in response to surrounding humidity, while showing good mechanical properties, which could open a new approach for developing biodegradable materials for functional packaging. The fabricated samples were tested for their photonic responses in relative humidity, mechanical behavior, water absorption capacity, and water contact angle
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
