Long-term stability of nanostructured polypyrrole electrochromic devices by using deep eutectic solvents

Preparation and Electrochromic Properties of MnO2/PPy Composite Films with Coral-like Structures

MnO2/polypyrrole (PPy) composite films were deposited on fluorine-doped tin oxide (FTO) conductive glasses by a two-step wet-chemical method, including electrochemical deposition and chemical bath deposition (CBD). The porous MnO2 films were first grown on FTO glasses by an electrodeposition method. Second, polypyrrole nanoparticles were polymerized by the oxidation-reduction reaction between MnO2 and pyrrole, using the presynthesized MnO2 as the skeleton. Then, MnO2/PPy composite films with coral-like structures were obtained. The electrochemical and electrochromic (EC) properties of the prepared films were investigated. The results show that, compared to the single MnO2 or PPy film, the MnO2/PPy composite film has a larger optical modulation (67.3% at a wavelength of 900 nm), faster response times (4 s for coloration and 3 s for bleaching), and a higher coloration efficiency (218.16 cm2·C-1). The high coloration efficiency attests to the exceptional performance of the composite film in converting electrical signals into vivid color changes. The electrochemical stability test results show that the composite film maintains a stable EC performance after 200 coloration/bleaching cycles. The coral-like structures of the composite film are responsible for the better EC properties.

Transdermal Delivery of Insulin Using Combination of Iontophoresis and Deep Eutectic Solvents as Chemical Penetration Enhancers: In Vitro and in Vivo Evaluations

A serious challenge in transdermal iontophoresis (IP) delivery of insulin (INS) is the low permeability of the drug across the skin. In this paper, we introduced deep eutectic solvent (DESs) as novel chemical penetration enhancers (CPEs) for transdermal IP of INS across rat skin, both in vitro and in vivo. Three different DESs based on choline chloride (ChCl), namely, ChCl/UR (ChCl and urea), ChCl/GLY (ChCl and glycerol), and ChCl/EG (ChCl and ethylene glycol) in the 1:2 molar ratios have been prepared. To evaluate the capability of studied DESs as CPEs for IP delivery of INS, the rat skin sample was treated with each DES. The effects of different experimental parameters (current density, formulation pH, INS concentration, NaCl concentration, and treatment time) on the in vitro transdermal iontophoretic delivery of INS were investigated. The in vitro permeation studies exhibited that INS was easily delivered employing ChCl/EG, and ChCl/GLY treatments, compared with ChCl/UR: the cumulative amount of permeated INS at the end of the experiment (Q24h) was found to be 131.0, 89.4, and 29.6 µg cm-2 in the presence of ChCl/EG, ChCl/GLY, and ChCl/UR, respectively. The differences in Q24h values of INS are due to the different capabilities of the studied DESs to treat the epidermis layer of skin. In vivo experiments revealed that the blood glucose level in diabetic rats could be decreased using ChCl/EG, and ChCl/GLY as novel CPEs in the IP delivery of INS. The presented work will open new doors towards searching for novel CPEs in the development of transdermal IP of INS.

Theoretical investigation of electrochromic mechanism in D-A conjugated polymers in visible and infrared bands

Electrochromic materials have been widely-applied in military camouflage and intelligent materials, in consideration of the multicolor display and infrared absorption. However, most of them have a narrow width of absorption spectra, and the electrochromic mechanism is still not well understood, especially in materials based on a copolymer structure in visible and infrared bands. Therefore, based on the polaron model, in order to enhance polarizability, we designed an "electronic donors-electronic acceptor" (D-A) type π-conjugated electrochromic polymer, which has an abundant color (wavelengths from 450 nm to 750 nm) with voltage range (from -0.2 V to 1.0 V). Employing first-principle calculations, we investigated the electrochromism of the polymer, which has a strong connection with the introduced new molecular orbital in the polaron (or cation), comparing with those in the neutral molecule. This study addressed the underlying mechanism for the electrochromic phenomenon and the behavior of the cation. It indicated the polaron molecular orbitals provide the photon absorption, whose energies are in the visible range and result in the electrochromic abundant color. In this work, we provide a molecular design for the adjustment of visible and infrared band absorption, which could have broad application in multicolor and infrared electrochromic materials.

Polypyrrole Nanomaterials: Structure, Preparation and Application

In the past decade, nanostructured polypyrrole (PPy) has been widely studied because of its many specific properties, which have obvious advantages over bulk-structured PPy. This review outlines the main structures, preparation methods, physicochemical properties, potential applications, and future prospects of PPy nanomaterials. The preparation approaches include the soft micellar template method, hard physical template method and templateless method. Due to their excellent electrical conductivity, biocompatibility, environmental stability and reversible redox properties, PPy nanomaterials have potential applications in the fields of energy storage, biomedicine, sensors, adsorption and impurity removal, electromagnetic shielding, and corrosion resistant. Finally, the current difficulties and future opportunities in this research area are discussed.

Spectroelectrochemistry of Electroactive Polymer Composite Materials

In this review, we have summarized the main advantages of the method of spectroelectrochemistry as applied to recent studies on electrosynthesis and redox processes of electroactive polymer composite materials, which have found wide application in designing organic optoelectronic devices, batteries and sensors. These polymer composites include electroactive polymer complexes with large unmovable dopant anions such as polymer electrolytes, organic dyes, cyclodextrins, poly(β-hydroxyethers), as well as polymer-inorganic nanocomposites. The spectroelectrochemical methods reviewed include in situ electron absorption, Raman, infrared and electron spin resonance spectroscopies.

Silver Nanowire-Based Printable Electrothermochromic Ink for Flexible Touch-Display Applications

Flexible, lightweight, low-power, and low-cost displays are an active area of interest in the electronics community. In this work, we have developed a composite electrothermochromic material consisting of silver nanowires (Ag NWs) and thermochromic powders, which exhibits reversible color (phase) change during biasing due to Joule heating. A wide variety of color combinations are possible with suitable thermochromic material selection. We have formulated this composite material as a printable ink so that patterned deposition can be achieved in a single step. A low processing temperature of 100 °C makes the composite compatible with a wide range of flexible substrates such as paper and polyethylene terephthalate (PET). The material (encapsulated with polydimethylsiloxane (PDMS)) exhibits good flexibility and is observed to be functional after 10 000 bending cycles with <7% resistance change. We have fabricated a low-power seven-segment color display to show the material's suitability for practical display applications. We have also demonstrated that the same layer can function as a display and as a touch sensor because of its conducting and chromatic properties without additional active layers on top. The material is suitable for the fabrication of low-cost, flexible touch color displays for interactive electronic readers, digital posters, and flexible digital signboards.

Hybrid Nanocomposite Platform, Based on Carbon Nanotubes and Poly(Methylene Blue) Redox Polymer Synthesized in Ethaline Deep Eutectic Solvent for Electrochemical Determination of 5-Aminosalicylic Acid

A novel hybrid composite of conductive poly(methylene blue) (PMB) and carbon nanotubes (CNT) was prepared for the detection of 5-aminosalicylic acid (5-ASA). Electrosynthesis of PMB with glassy carbon electrode (GCE) or with carbon nanotube modified GCE was done in ethaline deep eutectic solvent of choline chloride mixed with ethylene glycol and a 10% v/v aqueous solution. Different sensor architectures were evaluated in a broad range of pH values in a Britton-Robinson (BR) buffer using electrochemical techniques, chronoamperometry (CA), and differential pulse voltammetry (DPV), to determine the optimum sensor configuration for 5-ASA sensing. Under optimal conditions, the best analytical performance was obtained with CNT/PMB_DES/GCE in 0.04 M BR buffer pH 7.0 in the range 5-100 µM 5-ASA using the DPV method, with an excellent sensitivity of 9.84 μA cm^-2 μM^-1 (4.9 % RSD, n = 5) and a detection limit (LOD) (3σ/slope) of 7.7 nM, outclassing most similar sensors found in the literature. The sensitivity of the same sensor obtained in CA (1.33 μA cm^-2 μM^-1) under optimal conditions (pH 7.0, E_app = +0.40 V) was lower than that obtained by DPV. Simultaneous detection of 5-ASA and its analogue, acetaminophen (APAP), was successfully realized, showing a catalytic effect towards the electro-oxidation of both analytes, lowering their oxidation overpotential, and enhancing the oxidation peak currents and peak-to-peak separation as compared with the unmodified electrode. The proposed method is simple, sensitive, easy to apply, and economical for routine analysis.