Polyaniline Emeraldine Salt in the Amorphous Solid State: Polaron versus Bipolaron

Lignosulfonate-doped polyaniline-reinforced poly(vinyl alcohol) hydrogels as highly sensitive, antimicrobial, and UV-resistant multifunctional sensors

Flexible wearable strain sensors exist the advantages of high resolution, lightweight, wide measurement range, which have unlimited potential in fields such as soft robotics, electronic skin, and artificial intelligence. However, current flexible sensors based on hydrogels still have some defects, including poor mechanical properties, self-adhesive properties and bacteriostatic properties. In this study, A conductive hydrogel Sodium Ligninsulfonate (LGS)@PANI-Ag-poly(vinyl alcohol) (PVA) hydrogels consisting of lignosulfonate-doped polyaniline (LGS@PANI), silver nitrate, and PVA interactions were designed and prepared for sensing applications. Here, the abundant reactive functional groups of lignosulfonates not only improve the electrochemical and electrical conductivity of polyaniline, thereby increasing its potential for sensing and capacitor applications, but also provide excellent mechanical properties (0.71 MPa), self-adhesion (81.27 J/m2) and ultraviolet (UV) resistance (UV inhibition close to 100 %) to the hydrogel. In addition, the hydrogel exhibited rich multifunctional properties, including tensile strain resistance (up to 397 %), antimicrobial properties (up to 100 % inhibition of Escherichia coli and Staphylococcus aureus), high sensitivity (gauge factor, GF = 4.18), and a rapid response time (100 ms). The LGS@PANI-Ag-PVA hydrogels showed potential for wearable sensors that monitor various biosignals from the human body, as well as human-computer interaction, artificial intelligence and other diverse fields.

Dynamic Nuclear Polarization with Conductive Polymers

The low sensitivity of liquid-state nuclear magnetic resonance (NMR) can be overcome by hyperpolarizing nuclear spins by dissolution dynamic nuclear polarization (dDNP). It consists of transferring the near-unity polarization of unpaired electron spins of stable radicals to the nuclear spins of interest at liquid helium temperatures, below 2 K, before melting the sample in view of hyperpolarized liquid-state magnetic resonance experiments. Reaching such a temperature is challenging and requires complex instrumentation, which impedes the deployment of dDNP. Here, we propose organic conductive polymers such as polyaniline (PANI) as a new class of polarizing matrices and report 1H polarizations of up to 5 %. We also show that 13C spins of a host solution impregnated in porous conductive polymers can be hyperpolarized by relayed DNP. Such conductive polymers can be synthesized as chiral and display current induced spin selectivity leading to electron spin hyperpolarization close to unity without the need for low temperatures nor high magnetic fields. Our results show the feasibility of solid-state DNP in conductive polymers that are known to exhibit chirality-induced spin selectivity.

Polyaniline-graphene based composites electrode materials in supercapacitor: synthesis, performance and prospects

Supercapacitors (SCs) have become one of the most popular energy-storage devices for high power density and fast charging/discharging capability. Polyaniline is a class of conductive polymer materials with ultra-high specific capacitance, and the excellent mechanical properties will play a key role in the research of flexible SCs. The synergistic effect between polyaniline and graphene is often used to overcome their respective inherent shortcomings, thus the high-performance polyaniline-graphene based nanocomposite electrode materials can be prepared. The development of graphene-polyaniline nanocomposites as electrode materials for SCs depends on their excellent microstructure design. However, it is still difficult to seek a balance between graphene performance and functionalization to improve the weak interfacial interaction between graphene and polyaniline. In this manuscript, the latest preparation methods, research progress and research results of graphene-polyaniline nanocomposites on SCs are reviewed, and the optimization of electrode structures and performances is discussed. Finally, the prospect of graphene-polyaniline composites is expected.

Iontophoretically controlled insulin delivery via water-soluble conductive polymer PANI:PSS and thermoplastic polyurethane matrix

Transdermal insulin delivery is an alternative route to deliver insulin through the body skin with the challenges to overcome the low drug skin permeability and high molecular weight. Polyaniline doped with poly(4-styrenesulfonic acid) (PANI:PSS), a conductive polymer with the high electrical conductivity, was synthesized and utilized as a drug carrier to improve the drug delivery capability from a porous thermoplastic polyurethane (TPU) matrix. The insulin was electrostatically attached to PANI:PSS based on the ion exchange between insulin and PSS. For the in vitro drug release of insulin loaded PANI:PSS relative to the pristine insulin alone, the amount of insulin released was improved to 84.70% with the time to equilibrium of 2 h under the electrical field of 6 V. For the ex vivo release-skin permeation, the amount insulin released and permeated became lower at 57.02% with time to equilibrium of 2 h, due to the pig skin acting as a barrier for insulin permeation. The modified insulin transdermal delivery, with PANI:PSS as the drug carrier and drug enhancer relative to without, is shown here to influence the insulin release rate, amount, and duration, suitable to treat diabetes patients.

Extremely Suppressed Energetic Disorder in a Chemically Doped Conjugated Polymer

Chemical doping can be used to tune the optoelectronic properties of conjugated polymers (CPs), extending their applications as conducting materials. Unfortunately, chemically doped CP films containing excess dopants exhibit an increase in energetic disorder upon structural alteration, and Coulomb interactions between charge carriers and dopants also affect such disorder. The increase in energetic disorder leads to a broadening of the density of states, which consequently impedes efficient charge transport in chemically doped CPs. However, the molecular origins that are inherently resistant to such incidental increase of energetic disorder in chemically doped CPs have not been sufficiently explored. Here, it is discovered that energetic disorder in chemically doped CPs can be suppressed to a level close to the theoretical limit. Indacenodithiophene-co-benzothiadiazole (IDTBT) doped with triethyloxonium hexachloroantimonate (OA) exhibits disorder-free charge-transport characteristics and band-like transport behavior with astonishing carrier mobility as a result of reinforced 1D intramolecular transport. Molecular structure of IDTBT provides a capability to lower the energetic disorder that generally arises from the inclusion of heterogeneous dopants. The results suggest the possibilities of implementing disorder-free CPs that exhibit excellent charge transport characteristics in the chemically doped state and satisfy a prerequisite for their availability in the industry.

Natural Glycyrrhizic Acid-Tailored Homogeneous Conductive Polyaniline Hydrogel as a Flexible Strain Sensor

Polyaniline (PANi) hydrogels often exhibit highly mechanical and electrochemical properties, which have received extensive attention in the fields of batteries, supercapacitors, and sensors. However, the shortcomings such as hydrophobicity and easy aggregation of PANi frequently result in deterioration of mechanical and electrochemical performance of PANi hydrogels. Here, a bifunctional natural product, glycyrrhizic acid (GL), is utilized to prepare the homogeneous conductive PANi hydrogel, because GL not only can assemble into supramolecular hydrogel as the biocompatible matrix but also can salinize aniline monomers to facilitate the polymerization in situ to form uniformly dispersed PANi within GL matrix. Accordingly, the resulting GL/PANi hydrogel shows the Tyndall effect caused by the nanoclusters entangled by nanofibers and exhibits an improved storage modulus G' (3.2 kPa) and loss modulus G″ (0.9 kPa), as well as the expected conductivity (0.17 S·m^-1). In addition, the GL/PANi hydrogel is further reinforced by blending poly(vinyl alcohol) (PVA) for the required strength and stretchability as a flexible strain sensor. The results reveal that the obtained PVA/GL/PANi hydrogel has a fracture stress of 693 kPa at an elongation of 329%, with a fracture toughness of 82 MJ·m^-3 and Young's modulus of 47.9 kPa. Its gauge factor (GF) is measured to be 2.5 at lower strain (<130%) and up to 4.3 at larger strain (>130%). This good sensitivity and sensing stability make the PVA/GL/PANi hydrogel effectively monitor relevant human motion detections. Our work provides an innovative strategy to manufacture the homogeneous conductive PANi hydrogel for high-performance soft electronic devices.

Progress of Polyaniline Glucose Sensors for Diabetes Mellitus Management Utilizing Enzymatic and Non-Enzymatic Detection

Glucose measurement is a fundamental tool in the daily care of Diabetes Mellitus (DM) patients and healthcare professionals. While there is an established market for glucose sensors, the rising number of DM cases has promoted intensive research to provide accurate systems for glucose monitoring. Polyaniline (PAni) is a conductive polymer with a linear conjugated backbone with sequences of single C-C and double C=C bonds. This unique structure produces attractive features for the design of sensing systems such as conductivity, biocompatibility, environmental stability, tunable electrochemical properties, and antibacterial activity. PAni-based glucose sensors (PBGS) were actively developed in past years, using either enzymatic or non-enzymatic principles. In these devices, PAni played roles as a conductive material for electron transfer, biocompatible matrix for enzymatic immobilization, or sensitive layer for detection. In this review, we covered the development of PBGS from 2015 to the present, and it is not even exhaustive; it provides an overview of advances and achievements for enzymatic and non-enzymatic PBGB PBGS for self-monitoring and continuous blood glucose monitoring. Additionally, the limitations of PBGB PBGS to advance into robust and stable technology and the challenges associated with their implementation are presented and discussed.

Operando Characterization of Organic Mixed Ionic/Electronic Conducting Materials

Operando characterization plays an important role in revealing the structure-property relationships of organic mixed ionic/electronic conductors (OMIECs), enabling the direct observation of dynamic changes during device operation and thus guiding the development of new materials. This review focuses on the application of different operando characterization techniques in the study of OMIECs, highlighting the time-dependent and bias-dependent structure, composition, and morphology information extracted from these techniques. We first illustrate the needs, requirements, and challenges of operando characterization then provide an overview of relevant experimental techniques, including spectroscopy, scattering, microbalance, microprobe, and electron microscopy. We also compare different in silico methods and discuss the interplay of these computational methods with experimental techniques. Finally, we provide an outlook on the future development of operando for OMIEC-based devices and look toward multimodal operando techniques for more comprehensive and accurate description of OMIECs.

Linear and star-shaped π-conjugated oligoanilines: a review on molecular design in syntheses and properties

Molecular Design and Synthesis of Linear and Star-shaped π-conjugated Oligoanilines with reversible optoelectrochemical properties.

Iridium and Ruthenium Modified Polyaniline Polymer Leads to Nanostructured Electrocatalysts with High Performance Regarding Water Splitting

The breakthrough in water electrolysis technology for the sustainable production of H₂, considered as a future fuel, is currently hampered by the development of tough electrocatalytic materials. We report a new strategy of fabricating conducting polymer-derived nanostructured materials to accelerate the electrocatalytic hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and water splitting. Extended physical (XRD, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX)) and electrochemical (cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS)) methods were merged to precisely characterize the as-synthesized iridium and ruthenium modified polyaniline (PANI) materials and interrogate their efficiency. The presence of Ir(+III) cations during polymerization leads to the formation of Ir metal nanoparticles, while Ru(+III) induces the formation of RuO₂ oxide nanoparticles by thermal treatment; they are therefore methods for the on-demand production of oxide or metal nanostructured electrocatalysts. The findings from using 0.5 M H₂SO₄ highlight an ultrafast electrochemical kinetic of the material PANI-Ir for HER (36 - 0 = 36 mV overpotential to reach 10 mA cm^-2 at 21 mV dec^-1), and of PANI-Ru for OER (1.47 - 1.23 = 240 mV overpotential to reach 10 mA cm^-2 at 47 mV dec^-1), resulting in an efficient water splitting exactly at its thermoneutral cell voltage of 1.45 V, and satisfactory durability (96 h).

Significant role of thorny surface morphology of polyaniline on adsorption of triiodide ions towards counter electrode in dye-sensitized solar cells

Revealing the adsorption behavior of polyaniline with thorny surface morphology towards triiodide ions and its impact on the dye-sensitized solar cell performance.

Radical addition polymerization: Enzymatic template-free synthesis of conjugated polymers and their nanostructure fabrication

Conjugated polymers are attractive for many applications due to their unique properties. Their molecular structure can easily be tuned, making them suitable for an enormous number of specific applications. Conjugated polymers have the potential to achieve electrical properties similar to those of noncrystalline inorganic semiconductors; however, their chemical structure is much more complex and somewhat resembles that of biomacromolecules. The molecular conformation and interactions of conjugated polymers play an important role in their functionality. The use of enzymes has emerged as a highly valuable alternative method to synthesize these polymers and is very useful in the fabrication of their nanostructures. Here, we present established strategies for the synthesis of conjugated polymers in template-free systems that do not interfere with the preparation of their nanostructures. These strategies are based on the use of peroxidases (class III; EC 1.11.1.7, donor: hydrogen peroxide oxidoreductase), which are enzymes that have the ability to catalyze the oxidation of a number of compounds (including aromatics such as aniline, pyrrole, thiophene and some of their derivatives), in the presence of hydrogen peroxide, to obtain conjugated polymers.

Doping engineering of conductive polymer hydrogels and their application in advanced sensor technologies

Conductive polymer hydrogels are emerging as an advanced electronic platform for sensors by synergizing the advantageous features of soft materials and organic conductors. Doping provides a simple yet effective methodology for the synthesis and modulation of conductive polymer hydrogels. By utilizing different dopants and levels of doping, conductive polymer hydrogels show a highly flexible tunability for controllable electronic properties, microstructures, and structure-derived mechanical properties. By rationally tailoring these properties, conductive polymer hydrogels are engineered to allow sensitive responses to external stimuli and exhibit the potential for application in various sensor technologies. The doping methods for the controllable structures and tunable properties of conductive polymer hydrogels are beneficial to improving a variety of sensing performances including sensitivity, stability, selectivity, and new functions. With this perspective, we review recent progress in the synthesis and performance of conductive polymer hydrogels with an emphasis on the utilization of doping principles. Several prototype sensor designs based on conductive polymer hydrogels are presented. Furthermore, the main challenges and future research are also discussed.

Complex dielectric transformation of UV-vis diffuse reflectance spectra for estimating optical band-gap energies and materials classification

In this work, a complex dielectric transformation of UV-vis diffuse reflectance spectra is proposed to estimate the optical band-gap energies of an array of materials classified as semi-conductors, conductors and insulators and the results are compared with the more common Kubelka–Munk (K–M) transformation.