Chitin is an abundant biopolymer whose natural production is second only to cellulose. Similar to cellulose nanocrystals (CNCs) or nanofibers (CNFs), chitin nanofibers (ChNFs) can be isolated and used as sustainable O 2 barrier materials for food, electronics, and pharmaceutical packaging. These bioavailable nanomaterials are readily dispersed in water enabling spray-coated films to be deposited at high rates onto uneven or delicate surfaces. In the present study, we demonstrate the successful layer-by-layer spray coating of cationic ChNF and anionic CNC suspensions onto poly(lactic acid) (PLA) films. ChNF/CNC multilayers were found to lead to a reduction in the O 2 permeability of the final composite film by as much as 73% with the largest effects seen in composites with three alternating layers (ChNF-CNC-ChNF). Multilayer ChNF/CNC coatings were found to have lower O 2 permeability and lower haze than those coated with ChNF or CNCs alone (72% and 86% lower haze, respectively), pointing to a synergistic effect. The composites had a water vapor transmission rate similar to the PLA substrate.

Transparent wood composites, with their high strength and toughness, thermal insulation, and excellent transmissivity, offer a route to replace glass for diffusely transmitting windows. Here, conjugated‐polymer‐based electrochromic devices (ECDs) that switch on‐demand are demonstrated using transparent wood coated with poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as a transparent conducting electrode. These ECDs exhibit a vibrant magenta‐to‐clear color change that results from a remarkably colorless bleached state. Furthermore, they require low energy and power inputs of 3 mWh m−2 at 2 W m−2 to switch due to a high coloration efficiency (590 cm2 C−1) and low driving voltage (0.8 V). Each device component is processed with high‐throughput methods, which highlights the opportunity to apply this approach to fabricate mechanically robust, energy‐efficient smart windows on a large scale.

The processability and electronic properties of conjugated polymers (CPs) have become increasingly important due to the potential of these materials in redox and solid-state devices for a broad range of applications. To solubilize CPs, side chains are needed, but such side chains reduce the relative fraction of electroactive material in the film, potentially obstructing π−π intermolecular interactions, localizing charge carriers, and compromising desirable optoelectronic properties. To reduce the deleterious effects of side chains, we demonstrate that postprocessing side chain removal, exemplified here via ester hydrolysis, significantly increases the electrical conductivity of chemically doped CP films. Beginning with a model system consisting of an ester functionalized ProDOT copolymerized with a dimethylProDOT, we used a variety of methods to assess the changes in polymer film volume and morphology upon hydrolysis and resulting active material densification. Via a combination of electrochemistry, X-ray photoelectron spectroscopy, and charge transport models, we demonstrate that this increase in electrical conductivity is not due to an increase in degree of doping but an increase in charge carrier density and reduction in carrier localization that occurs due to side chain removal. With this improved understanding of side chain hydrolysis, we then apply this method to high-performance ProDOT-alt-EDOT x copolymers. After hydrolysis, these ProDOT-alt-EDOT x copolymers yield exceptional electrical conductivities (∼700 S/cm), outperforming all previously reported oligoether-/glycol-based CP systems. Ultimately, this methodology advances the ability to solution process highly electrically conductive CP films.

As environmental considerations for both the processing and disposal of electronic devices become increasingly important, the ability to replace plastic and glass substrates with bioderived and biodegradable materials remains a major technological goal. Here, the use of cellulose nanofiber-coated paper is explored as an environmentally benign substrate for preparing low-resistance (460 Ω sq −1 ), colorless (a* = −2.3, b* = −2.7) printed poly-(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) electrodes. The PEDOT:PSS/paper electrodes support the reversible oxidation of three electrochromic polymers (ECPs) (cyan, magenta, and yellow), affording the possibility for fully printed, color displays on paper. Lateral electrochromic devices (ECDs) incorporating an ion gel electrolyte are demonstrated where a magenta-to-colorless device achieves a color contrast (ΔE*) of 56 owing to a highly color-neutral bleached state of the ECP (a* = −0.5, b* = 2.9). Black-tocolorless devices achieve ΔE* = 29 and are able to retain 86% of their color contrast after 9000 switches. The switching times of these lateral devices are quantified through colorimetric image analysis which shows comparable performance for devices constructed on paper as devices using ITO/glass electrodes (10 Ω sq −1 ). The paper ECDs are then combusted in air leaving 3% of the initial mass at 600 °C, highlighting this approach as a promising route toward disposable displays. Figure 2. Optimization of printed electrodes showing a) reflectance as a function of sheet resistance for printed electrodes on glass, CNF coated paper, and office paper. Photographs of PEDOT:PSS electrodes on CNF coated paper with sheet resistances of b) 5000 Ω sq −1 , c) 460 Ω sq −1 , d) 160 Ω sq −1 , and e) 109 Ω sq −1 . CIELAB color coordinates are labeled below each image. www.afm-journal.de www.advancedsciencenews.com 1903487 (4 of 11)

The growing range of applications for optoelectronic and electrochromic devices (ECDs) encourages the search for materials combining high electrical conductivity with optical transparency. Next generation transparent conducting electrodes (TCEs) are required to be inexpensive, lightweight, scalable, and compatible with flexible substrates to trigger innovations towards supporting sustainable living and reducing energy consumption. Here we show that PEDOT:PSS can be solution processed using blade coating and subsequently post-treated with nitric and acetic acid to raise its conductivity above 2000 S cm with a film transparency of ∼95%. A combined grazing-incidence wide angle X-ray scattering, atomic force microscopy, and thickness analysis of the film indicates that the removal of excess insulating PSS inducing reordering is the critical parameter for the claimed conductivity increase. We then investigate the impact of replacing indium tin oxide electrodes with PEDOT:PSS in ECDs. While electrochromic contrast and optical memory are comparable for devices constructed with both electrode materials, differences in switching kinetics are explored by comparing internal resistances, ion diffusion, and charging effects in the polymer films extracted by electrochemical impedance spectroscopy. While all these ideas are described based on a battery-type ECD configuration, these concepts are easily transferable to other types of redox-active devices.

The ability to process conjugated polymers via aqueous solution is highly advantageous for reducing the costs and environmental hazards of large scale roll-to-roll processing of organic electronics. However, maintaining competitive electronic properties while achieving aqueous solubility is difficult for several reasons: (1) Materials with polar functional groups that provide aqueous solubility can be difficult to purify and characterize, (2) many traditional coupling and polymerization reactions cannot be performed in aqueous solution, and (3) ionic groups, though useful for obtaining aqueous solubility, can lead to a loss of solid-state order, as well as a screening of any applied bias. As an alternative, we report a multistage cleavable side chain method that combines desirable aqueous processing attributes without sacrificing semiconducting capabilities. Through the attachment of cleavable side chains, conjugated polymers have for the first time been synthesized, characterized, and purified in organic solvents, converted to a water-soluble form for aqueous processing, and brought through a final treatment to cleave the polymer side chains and leave behind the desired electronic material as a solvent-resistant film. Specifically, we demonstrate an organic soluble polythiophene that is converted to an aqueous soluble polyelectrolyte via hydrolysis. After blade coating from an aqueous solution, UV irradiation is used to cleave the polymer’s side chains, resulting in a solvent-resistant, electroactive polymer thin film. In application, this process results in aqueous printed materials with utility for solid-state charge transport in organic field effect transistors (OFETs), along with red to colorless electrochromism in ionic media for color changing displays, demonstrating its potential as a universal method for aqueous printing in organic electronics.

The demand for packaging materials with low gas permeabilities is increasing, but commonly used petroleum-derived single-use plastics are not renewable, biodegradable, or easy to recycle. Nanomaterials composed of chitin and cellulose, which are abundant in nature, have high crystallinities and low oxygen permeabilities (OPs), providing a viable alternative. In this work, we explore how deacetylation conditions of crab shell chitin can be used to tune the charge and size of the resulting chitin nanowhiskers (ChNWs) and the resulting OP of layered film structures. Three deacetylation factors, the concentration of sodium hydroxide (% NaOH), temperature (T), and reaction time, were explored using a three-factor three-level Taguchi design with an orthogonal array. The resulting ChNW suspensions were sequentially spray-coated with suspensions of cellulose nanocrystals (CNCs) onto cellulose acetate (CA) films to form a multilayer structure. We show that ChNWs prepared under more aggressive deacetylation conditions inside the original orthogonal array (higher % NaOH, T, and time) had shorter lengths but the surface charge was significantly influenced only by more aggressive deacetylation outside of the original design conditions. With only ∼10% decrease in the ultimate tensile strength and no significant loss in failure strain, the ChNW–CNC coating resulted in ∼20% decrease in the water vapor transmission rate in comparison to uncoated CA films. The optimization of process conditions resulted in CA-ChNW-CNC films with a 91–99% decrease in OP (132–16.7 cm3·μm/m2/day/kPa vs 1553 cm3·μm/m2/day/kPa for uncoated CA).

Water soluble-solvent resistant approach for aqueous supercapacitors.