Precisely tuned photonic properties of crystalline nanocellulose biocomposite coatings by gradually tailored nanoarchitectures

A feasibility study on femtosecond laser texturing of sprayed nanocellulose coatings

Nanocelluloses are emerging as natural materials with favourable properties for coating industry and can be applied by state-of-the-art spraying technology. While additional functionalities are commonly introduced through chemical modification, the surface microstructuring of nanocellulose coatings with high throughput methods remains unexplored. Here, a femtosecond laser is used for texturing spray-coated coatings made of cellulose nanofibrils (CNF) or cellulose nanocrystals (CNC). For coating thickness of 1.5 to 8 μm, processing limits were determined with maximum ablation energy linearly increasing with coating thickness and minimum ablation energy decreasing or increasing depending on the apparent coating density. Within applicable processing window of pulse rate and power setting, the operational ranges were determined for creating one-dimensional and two-dimensional surface patterns, requiring a higher laser energy for CNC compared to CNF coatings and yielding thinnest possible resolved patterns of 17 μm as determined by the laser spot diameter. The laser ablation under low energy corresponds to an increase in surface roughness and intensifies surface hydrophilicity, while the line patterns are able to pin water droplets with rising water contact angles up to 90°. Present feasibility study opens future possibilities for managing surface properties of nanocellulose coatings in applications where tuning of surface hydrophilicity is required.

Controllable hydrophilic/superhydrophobic patterned coatings for optical information encryption/decryption based on water-triggered opaque to translucent transition

Anti-counterfeiting technologies are crucial for securing the authenticity and proof of commodities, in which the optical information encryption/decryption has attracted extensive attention for its overriding advantages of visibility and convenience. Inspired by the unique transparency transformation phenomenon of Diphylleia grayi petals, a controllable hydrophilic/superhydrophobic patterned coating with water-triggered opaque to translucent transition is proposed through the construction of a superhydrophobic coating, subsequent air plasma etching under a mask, and final hydrophilic modification to introduce stable invisible patterns. The superhydrophobic region exhibits great water repellency with a water contact angle (WCA) at 157°, while the hydrophilic region quickly absorbs water with a WCA at 61°. The patterned coating presents an opaque state for the serious light scattering induced by the rough microstructure and large refractive index difference between the coating and air, while the hydrophilic patterns on the coating transform to translucent after water infiltration for the reduced roughness and close refractive indexes of the coating and water. The information revealing is rapid and reversible, and demonstrates heat and long-term stability and great reusability. The findings conceivably stand out as a new methodology to fabricate controllable superwettable coatings with optical information encryption/decryption capability for application in anti-counterfeiting.

One-step wet-spinning of conducting polymer and cellulose nanofiber composites for fiber-type organic electrochemical transistors

Considering that textile-based sensors are suitable for monitoring/communicating human vital health information, organic electrochemical transistors (OECTs) are considered as an efficient device platform for augmenting the capabilities and effectiveness of smart textile applications in diverse areas. Herein, we investigated the fabrication process and properties of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)-TEMPO-oxidized cellulose nanofiber (CNF) composites as active channel materials for fiber-type OECTs. Utilizing highly crystalline, mechanically rigid, and chemically robust CNFs directly extracted from biomass-derived tunicate, we fabricated PEDOT:PSS-CNF composite fibers with varying CNF portions (0, 5, 10, 20, and 30 %) through a simple one-step wet-spinning process using sulfuric acid-based coagulation media. The addition of CNFs significantly improved the mechanical strength of the composite fibers with Young's modulus up to 13.4 ± 2.1 GPa. Moreover, the fiber-type OECT devices based on the PEDOT:PSS(80 %)-CNF(20 %) composite showed highest carrier mobility (4.0 ± 0.2 cm2 V-1 s-1) with the marginal trade-off in volumetric capacitance (57.1 ± 3.7 F/cm3), resulting in the decent benchmark performance parameter (μ·C*) of 229 F cm-1 V-1 s-1. Our findings suggest that the synergistic interaction between PEDOT:PSS and CNFs leads to a significant improvement in fiber properties, and the resulting composite fibers hold great potentials for use in eco-friendly wearable/textile electronics.

Recent advances in prevailing antifogging surfaces: structures, materials, durability, and beyond

In past decades, antifogging surfaces have drawn more and more attention owing to their promising and wide applications such as in aerospace, traffic transportation, optical devices, the food industry, and medical and other fields. Therefore, the potential hazards caused by fogging need to be solved urgently. At present, the up-and-coming antifogging surfaces have been developing swiftly, and can effectively achieve antifogging effects primarily by preventing fog formation and rapid defogging. This review analyzes and summarizes current progress in antifogging surfaces. Firstly, some bionic and typical antifogging structures are described in detail. Then, the antifogging materials explored thus far, mainly focusing on substrates and coatings, are extensively introduced. After that, the solutions for improving the durability of antifogging surfaces are explicitly classified in four aspects. Finally, the remaining big challenges and future development trends of the ascendant antifogging surfaces are also presented.