Doping of Polyaniline by Acid−Base Chemistry: Density Functional Calculations with Periodic Boundary Conditions

Competitive proton-trapping strategy enhanced anti-freezing organohydrogel fibers for high-strain-sensitivity wearable sensors

Stretchable organohydrogel fibers are attracting considerable interest for next-generation flexible and wearable soft strain sensors due to their excellent stability in harsh environments. However, due to the uniformly distributed ions and reduced number of carriers in the whole material, the sensitivity of organohydrogel fibers under subzero temperature is not desirable, which significantly hinders their practical application. Herein, a newly competitive proton-trapping strategy was designed to obtain anti-freezing organohydrogel fibers for high-performance wearable strain sensors via a simple freezing-thawing process, in which tetraaniline (TANI), serving as the proton trapper, and representing the shortest repeated structural unit of polyaniline (PANI), was physically crosslinked with polyvinyl alcohol (PVA) (PTOH). The as-prepared PTOH fiber exhibited an outstanding sensing performance at -40 °C due to the unevenly distributed ion carriers and the highly breakable proton-migration pathways, with a high gauge factor of 24.6 at a strain of 200-300%. Moreover, the existence of hydrogen bonds between the TANI and PVA chains endowed PTOH with a high tensile strength (1.96 MPa) and toughness (8.0 MJ m-3). Accordingly, strain sensors made from PTOH fibers and knitted textiles could monitor human motions rapidly and sensitively, demonstrating their potential as wearable anti-freezing anisotropic strain sensors.

Porous charged polymer nanosheets formed via microplastic removal from frozen ice for virus filtration and detection

We developed a method for producing porous charged polymer nanosheets using frozen ice containing microplastics. Upon assessing SARS-CoV-2 filtration using nanosheets with 100 nm-sized pores, a high rejection rate of 96% was achieved. The charged surfaces of nanosheets further enabled the electrophoretic capture of the virus using a portable battery with additional real-time sensing capability.

Electroactive aniline tetramer-spider silks with conductive and electrochromic functionality

Electroactive aniline tetramer-spider silk composite fibers with high conductivity and mechanical strength were developed using a dip coating method. The fabricated spider silk composite fibers retain the high mechanical strength (0.92 GPa) and unique reversible relaxation-contraction behavior of spider dragline silks. The aniline tetramer modified on the silk surface imparted electroactive properties to the composite fibers. The color of aniline tetramer/spider silk composite fibers could be controlled by applying different pH values and voltages. Furthermore, the composite fiber's resistivity could reach 186 Ω m which can conduct electrical current to light LEDs. This study could provide a valuable guideline for developing highly-conductive electrochromic spider silks for use in E-textiles.

DFT modeling of polyaniline: a computational investigation into the structure and band gap of polyaniline

The band gaps of three forms of polyaniline (PANI) are calculated using the DFT method with the B3LYP functional and SV(P) basis set. This marks the first time that the band gap for this polymer has been calculated using this DFT method. The calculations include an investigation of the effect of varying the benzoid–quinoid structural units, the effect of increasing oligomer length, and the inclusion of Michael’s addition structures, which could be residual in the polymer depending on the chosen synthetic method. All results were compared with the experimentally determined band gap of 1.5 eV as typically reported in the literature. A commonly used structural motif of alternating benzoid–quinoid units and a ratio of 0.5:0.5 benzoid–quinoid resulted in a computed band gap of 1.9 eV. Inclusion of one extra quinoid unit gave rise to a band gap of 1.3 eV. Incorporation of a Michael’s addition structure was found to dominate the band gap calculation, yielding a localized LUMO and a band gap of 1.3 eV that was insensitive to the polymer chain length and composition.

Theoretical Studies of Conducting Polymers: A Mini Review

The present short review discusses the computational studies carried out on polyacetylene (PAc), polyaniline (PANI), polypyrrole (PPy), and other conducting polymers for predicting their electronic, optoelectronic and structural properties. Studies...

Elimination of cationic azodye from aqueous media using doped polyaniline (PANI): adsorption optimization and modeling

An adsorbent doped polyaniline (PANI) has been explored for the elimination of a cationic azodye, basic red 46 (BR-46), from textile effluent. Essential factors from batch mode have been studied to investigate their effect on the removal of BR-46. The investigated data have been applied to two prevalent adsorption isothermal models (i.e., Langmuir and Freundlich). In addition to the coefficients of determination, six different statistical error functions have been used to identify the most appropriate model for the existing process. The Langmuir model has been shown to be the best adsorption isotherm with minimum error values and a high coefficient of determination value (R2 > 0.999). The maximum monolayer adsorption capacity observed was 1.83 × 10−4 mol g−1 at 50 °C. Thermodynamic parameters of Gibb’s free energy, enthalpy, and entropy were found to be –30.06 KJ mol−1, 374 J mol−1, and 97.25 J mol−1 K−1, respectively. The positive values of enthalpy and entropy indicate the process to be endothermic. The amount of the dye adsorbed increased from 1.02 to 5.42 × 10−5 g in moving from 30 to 50 °C. The measured energy of activation was 17.467 kJ mol−1. The maximum percent removal of BR-46 from wastewater has been 93% at pH 8.

Extraordinary electrochemical stability and extended polaron delocalization of ladder-type polyaniline-analogous polymers

Electrochemical stability and delocalization of states critically impact the functions and practical applications of electronically active polymers. Incorporation of a ladder-type constitution into these polymers represents a promising strategy to enhance the aforementioned properties from a fundamental structural perspective. A series of ladder-type polyaniline-analogous polymers are designed as models to test this hypothesis and are synthesized through a facile and scalable route. Chemical and electrochemical interconversions between the fully oxidized pernigraniline state and the fully reduced leucoemeraldine state are both achieved in a highly reversible and robust manner. The protonated pernigraniline form of the ladder polymer exhibits unprecedented electrochemical stability under highly acidic and oxidative conditions, enabling the access of a near-infrared light-absorbing material with extended polaron delocalization in the solid-state. An electrochromic device composed of this ladder polymer shows distinct switching between UV- and near-infrared-absorbing states with a remarkable cyclability, meanwhile tolerating a wide operating window of 4 volts. Taken together, these results demonstrate the principle of employing a ladder-type backbone constitution to impart superior electrochemical properties into electronically active polymers.

In Situ Conformal Coating of Polyaniline on GaN Microwires for Ultrafast, Self-Driven Heterojunction Ultraviolet Photodetectors

Independent and zero-maintenance systems would be in urgent need in the near future internet of things. Here, we present high-performance, self-driven organic/inorganic heterojunction ultraviolet (UV) photodetectors (PDs) by in situ polymerization of polyaniline (PANI) on Gallium nitride microwires. The GaN microwires with a high crystalline quality are grown on patterned Si substrates by metal organic chemical vapor deposition. Using a facile in situ chemical polymerization method, PANI is conformally coated on the surface of GaN microwires. The constructed GaN/PANI hybrid microwire PD exhibits a high responsivity of 178 mA/W, a remarkable detectivity of 4.67 × 10¹⁴ jones, and an ultrafast UV photoresponse speed (rise time of 0.2 ms and fall time of 0.3 ms) under zero bias. The intimate heterojunction in the form of N-Ga-N bonds between GaN and PANI may account for the observed high performances. The presented self-driven microwire UV PDs featuring ultrahigh-speed (sub-millisecond) response to UV light may find applications in future nano/micro-photosensor networks.

An Ultrasensitive Silicon Photonic Ion Sensor Enabled by 2D Plasmonic Molybdenum Oxide

Silicon photonics has demonstrated great potential in ultrasensitive biochemical sensing. However, it is challenging for such sensors to detect small ions which are also of great importance in many biochemical processes. A silicon photonic ion sensor enabled by an ionic dopant-driven plasmonic material is introduced here. The sensor consists of a microring resonator (MRR) coupled with a 2D restacked layer of near-infrared plasmonic molybdenum oxide. When the 2D plasmonic layer interacts with ions from the environment, a strong change in the refractive index results in a shift in the MRR resonance wavelength and simultaneously the alteration of plasmonic absorption leads to the modulation of MRR transmission power, hence generating dual sensing outputs which is unique to other optical ion sensors. Proof-of-concept via a pH sensing model is demonstrated, showing up to 7 orders improvement in sensitivity per unit area across the range from 1 to 13 compared to those of other optical pH sensors. This platform offers the unique potential for ultrasensitive and robust measurement of changes in ionic environment, generating new modalities for on-chip chemical sensors in the micro/nanoscale.

Distribution of dopant ions around poly(3,4-ethylenedioxythiophene) chains: a theoretical study

The effect of counterions and multiple polymer chains on the properties and structure of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with ClO₄⁻ has been examined using density functional theory (DFT) calculations with periodic boundary conditions (PBCs).

Formyl-Modified Polyaniline for the Catalytic Dehydration of Fructose to 5-Hydroxymethylfurfural

We report an unprecedented solid organic-base catalyst, formyl-modified polyaniline (FS-PAN), for the dehydration of fructose to 5-hydroxymethylfurfural (HMF) with a high yield of 90.4 mol %. We demonstrate that the nitrogen atoms incorporated between the phenyl rings in the backbone of the polyaniline chain contribute to the basicity of the catalyst. The grafting of electron-withdrawing formyl groups to the imine nitrogen atoms leads to a significant increase of basicity of the polymer catalyst owing to the greater localization of electrons at the amide nitrogen atom formed. A linear dependence of the yield of HMF on the grafting level of formyl groups in FS-PAN indicates that the amide acts as the active phase. A possible reaction mechanism for this organic-base-catalyzed dehydration reaction is proposed. The side-reaction of HMF rehydration is inhibited thoroughly, and the condensation of any reaction intermediates to undesirable oligomers is restrained by this base catalyst. This organic-base catalyst can be recycled completely without loss of activity. This research highlights the first application of a highly effective and stable solid base catalyst for the transformation of renewable carbohydrates into fine chemicals.

Biomarker-specific conjugated nanopolyplexes for the active coloring of stem-like cancer cells

Stem-like cancer cells possess intrinsic features and their CD44 regulate redox balance in cancer cells to survive under stress conditions. Thus, we have fabricated biomarker-specific conjugated polyplexes using CD44-targetable hyaluronic acid and redox-sensible polyaniline based on a nanoemulsion method. For the most sensitive recognition of the cellular redox at a single nanoparticle scale, a nano-scattering spectrum imaging analyzer system was introduced. The conjugated polyplexes showed a specific targeting ability toward CD44-expressing cancer cells as well as a dramatic change in its color, which depended on the redox potential in the light-scattered images. Therefore, these polyaniline-based conjugated polyplexes as well as analytical processes that include light-scattering imaging and measurements of scattering spectra, clearly establish a systematic method for the detection and monitoring of cancer microenvironments.

First-principles study of the effect of functional groups on polyaniline backbone

We present a first-principles density functional theory study focused on how the chemical and electronic properties of polyaniline are adjusted by introducing suitable substituents on a polymer backbone. Analyses of the obtained energy barriers, reaction energies and minimum energy paths indicate that the chemical reactivity of the polyaniline derivatives is significantly enhanced by protonic acid doping of the substituted materials. Further study of the density of states at the Fermi level, band gap, HOMO and LUMO shows that both the unprotonated and protonated states of these polyanilines are altered to different degrees depending on the functional group. We also note that changes in both the chemical and electronic properties are very sensitive to the polarity and size of the functional group. It is worth noting that these changes do not substantially alter the inherent chemical and electronic properties of polyaniline. Our results demonstrate that introducing different functional groups on a polymer backbone is an effective approach to obtain tailored conductive polymers with desirable properties while retaining their intrinsic properties, such as conductivity.

Doping of polyaniline with 6-cyano-2-naphthol

The conductivity of polyaniline (PANI) is ascribed to its emeraldine salt (PANI-ES), which is formed by protonation of its emeraldine base (PANI-EB) by acids. Generally, mineral acids are used for this purpose, but the use of dopants and additives to maintain the required acidity provides an alternative method to the preparation of PANI-ES. The present work attempts to achieve the protonation by the use of a weak organic acid, namely, 6-cyano-2-naphthol (6CN2), which is generally used as a superphotoacid, as its excited state pKa is significantly smaller than its ground state pKa. The question here is if the protonation of the aniline moieties in PANI takes place and if it does, whether it takes place by dissociation of the ground state or the excited state of 6CN2. Room temperature conductance measurements were carried out to see the effect of doping. The formation of PANI-ES from PANI-EB has been monitored by UV-vis spectrophotometry. When a polar counterion is inserted into the polymer matrix, it changes the environment of the nearby chains by introducing defects, reorganization of charges as a result of interaction with the polymer. Morphological investigation was done using optical microscopy, field emission gun scanning electron microscopy (FEGSEM), and field emission gun transmission electron microscopy FEGTEM. The influence of 6CN2 on the crystallinity of the polymer was determined by X-ray diffraction (XRD).

Excited-state hydrogen-bonding dynamics of camphorsulfonic acid doped polyaniline: a theoretical study

We present a TDDFT study on excited-state hydrogen-bonding dynamics of a camphorsulfonic acid doped polyaniline complex.

A facile method for synthesis of polyaniline nanospheres and effect of doping on their electrical conductivity

The synthesis of polyaniline (PANI) nanospheres by a simple template-free method has been described. The polymerization of aniline in aqueous medium was accomplished using ammonium persulfate without any protonic acid. The UV-vis spectrum of PANI nanospheres displayed the characteristic absorption peak of π-π* transition of the benzenoid ring at 355 nm. The oxidation state of PANI nanospheres was identified with FT-IR spectroscopy by comparing the two bands at 1582 (ring stretching in quinoid unit) and 1498 cm(-1) (ring stretching in bezenoid unit). The X-ray diffraction patterns demonstrated the low crystalline nature of PANI nanospheres. The morphology of PANI nanospheres was spherical and the mean diameter of nanospheres was found in the range of 3-12 nm. The thermal behavior of PANI nanospheres was studied by thermogravimetric analysis. The effect of doping of HCl and H(2)SO(4) on PANI nanospheres was studied by measuring the current as a function of time of exposure. The high electrical conductivity of 6×10(-2) S cm(-1) was obtained for PANI nanospheres at their optimum doping state by 100 ppm HCl.

Vesicles as soft templates for the enzymatic polymerization of aniline

The feasibility of using surfactant vesicles as soft templates for the peroxidase-triggered polymerization of aniline was investigated. It was found that mixed anionic vesicles (diameter approximately 80 nm) composed of sodium dodecylbenzenesulfonate (SDBS) and decanoic acid (1:1, molar ratio) are promising templates. In the presence of the vesicles and horseradish peroxidase/hydrogen peroxide (H2O2) as initiator system, aniline polymerizes under optimized conditions at pH=4.3 to the desired conductive emeraldine form of polyaniline (PANI). The optimal polymerization conditions were elaborated, and some of the chemical and physicochemical aspects of the reaction system were investigated. After addition of aniline and peroxidase to the vesicles, aniline is only loosely associated with the vesicles, as shown by NOESY-NMR and zeta potential measurements. In contrast, the peroxidase strongly binds to the vesicle surface, as shown by fluorescence measurements using TNS (2-(p-toluidino)naphthalene-6-sulfonate) as vesicle membrane probe. This binding of the enzyme to the vesicle surface indicates that the polymerization reaction is initiated predominantly on the surface of the vesicles. Cryo-transmission electron microscopy indicates that the polymerization product remains associated with the vesicles on their surface. For short reaction times (30 s<t<60 s), it is shown that oligoanilines containing an excess of oxidized units are obtained, as shown by VIS/NIR spectroscopy and MALDI-TOF mass spectrometry. For longer reaction times (1 min<t<30 min), the relative amount of over oxidized units in PANI decreases until polymers are obtained which have a VIS/NIR spectrum that is typical for the emeraldine salt form of PANI (lambdamax approximately 1000 nm). The appearance of stable unpaired electrons during the reaction was demonstrated by EPR measurements, in full support of the in situ formation of the conductive emeraldine salt form of PANI. At the end of the reaction (after 1 h), the PANI formed remains homogenously dispersed in the aqueous solution thanks to the presence of the vesicles. No precipitation occurs on a time scale of at least several weeks. FTIR and 13C NMR measurements of the product isolated from the reaction mixture confirm the formation of the emeraldine form of PANI. If the polymerization reaction is carried out in the absence of vesicles but under otherwise identical reaction conditions, the outcome of the reaction is very different, i.e., no indication at all for the formation of the conductive form of PANI.

Degenerate intermolecular and intramolecular proton-transfer reactions: electronic structure of the transition states

Density functional theory (DFT) calculations are performed on a series of double and single proton-transfer reactions to study the variation in polarizations in complexes during the dynamics of proton transfer from one isoenergetic, hydrogen-bonded ground-state structure to the other. The isotropic average polarizability (alpha(av)) shows an interesting single-humped profile with a maxima coinciding with the transition state of the reaction. Similar profiles are also computed at Nd:YaG frequencies. The origin of the maximal polarizability at the transition state is traced to maximal charge separation and large D (donor)-A (acceptor) distances. Maximal polarizability for the transition state suggests an interesting, novel, and less memory extensive computational tool to locate the transition state for hydrogen-transfer reactions in hydrogen-bonded complexes.

Influence of external voltage on the reprotonated polyaniline films by Fourier Transform Infrared spectroscopy

In this paper, we reported the electrical fourier transform infrared (FT-IR) spectra measurements on the reprotonated polyaniline (PANI) thin films. Application of external voltage reduced the intensity in FT-IR spectra and resulted in the shift of band situation. The FT-IR spectra as a function of temperature were also conducted in order to investigate the effect of Joule heating. We found that the influence of CC of phenyl units and the CC of quinoid were quite different as a function of external voltage and temperature. The current-voltage (I-V) curves of the PANI film measured in the range of 0-175 V showed that the resistance kept constant at 0-75 V while it increased from 75 to 175 V. The I-V curves confirmed the presence of Joule heating effect during 75-175 V. According to the experiment results, we concluded that external voltage could produce large average hopping energy, which allowed the charge transfer by hopping between the conducting domains during 0-75 V. The deprotonation of PANI was caused by Joule heating effect, resulting in the decreasing conductivity from 75 to 175 V.

Optical Properties of Emeraldine Salt Polymers from Ab Initio Calculations: Comparison with Recent Experimental Data

We present the absorption coefficient alpha(omega), the transverse dielectric function epsilon(omega), the optical conductivity sigma(omega), and the reflectance R(omega) calculated for an emeraldine salt conducting polymer in its crystalline 3D polaronic structure. We utilize Kohn-Sham density functional theory (DFT) electronic wavefunctions and energies implemented in the expression of the macroscopic transverse dielectric function in the framework of the band theory without the electron-hole interaction. Contributions of intra-band transitions are taken into account by adding a Drude-like term to the dielectric function calculated ab initio. Comparison with optical properties, recently measured on high-quality emeraldine salts (Lee, K.; Cho, S.; Park, S. H.; Heeger, A. J.; Lee, C.-W.; Lee, S. H. Nature 2006, 441, 65), and with optical absorption spectra, recorded on other emeraldine salts, is very satisfactory. The calculated spectra are discussed in terms of energy-band structure, density of states, inter- and intra-band transitions, and transverse dielectric function.

MNDO-PM3 Study of the Early Stages of the Chemical Oxidative Polymerization of Aniline

The theoretical approach to the study of aniline polymerization mechanism has been based on the MNDO-PM3 semi-empirical quantum chemical computations of the heat of formation of aniline dimer and trimer intermediates. The oxidation in aqueous medium without added acid is analyzed. The aniline nitrenium cation is proposed to be the reactive electrophilic species generated by the oxidation of aniline with a two-electron oxidant, ammonium peroxydisulfate, in the initiation phase. 4-Aminodiphenylamine and its fully oxidized form, N-phenyl-1,4-benzoquinonediimine, are the main dimeric products. 2-Aminodiphenylamine and its fully oxidized form, N-phenyl-1,2-benzoquinonediimine, are the most important side products of aniline dimerization. The influence of protonation on the oxidizability of aniline and reaction intermediates was studied. The dominant aniline oligomers have been shown to be linear as well as branched. The importance of reactivity difference between fully oxidized aniline oligomers composed of odd or even numbers of constitutional aniline units is pointed out. The species with odd numbers of aniline units, having nitrenium cationic nature, are much more reactive. The oxidation combined with intramolecular cyclization reaction pathways leads to substituted phenazines, characteristic of two-dimensional PANI chain-growth.