Effects of solvent and electrolyte on the electrochromic behavior and degradation of chemically prepared polyaniline-poly(vinyl alcohol) composite films

Effects of solvent and electrolyte on the electrochromic behavior and degradation of polyaniline in nonaqueous aprotic media, as well as its electrochemical redox and degradation mechanisms, were investigated with chemically prepared polyaniline-poly (vinyl alcohol) composite films and polyaniline homogeneous films. Visible and FT-IR absorption spectra of the polyaniline films, oxidized electrochemically at various polarization potentials, showed that the mechanisms in aprotic media involved two successive oxidation processes. In contrast to aqueous systems, the higher oxidation process involved further anion insertion without deprotonation, and the degradation was due to partial formation of the electrochemically inactive quinonediimine structure at excessive polarization potentials. From investigations of solvent and electrolyte effects, it is suggested that the electrochromic behavior and degradation of polyaniline are influenced by the electron-donating and accepting ability of solvents, acceptor strength of electrolyte cations, and the nucleophilic character of electrolyte anions. It was also suggested that some anions like as well as protons, are constrained in the PVA matrix by specific electrostatic interactions and steric effects to improve the stability of polyaniline in the highly oxidized state. © 1994 John Wiley & Sons, Inc.     

Effects of acidity on the size of polyaniline-poly(sodium 4-styrenesulfonate) composite particles and the stability of corresponding colloids in water

The practical application of polyaniline-poly(sodium 4-styrenesulfonate) (PANI-PSS) composite particles has been held back by the low stability of their dispersed state in water. In this work, we present a general oxidation approach to prepare PANI-PSS composite nanoparticles that can form highly stable colloids in water or buffer over a wide range of pH from 1 to 11. We demonstrate that the size of the PANI-PSS composite particles can be controlled by the acidity of precursor solutions. It is hypothesized that the number of negatively charged sites on PSS, which can be affected by the acidity of the precursor solutions, plays an important role in determining the size of the PANI-PSS composite particles and the stability of corresponding colloids in water.     

ESCA and TOF-SIMS study on oxidised and reduced polypyrrole-poly(4-styrenesulfonate) free-standing films synthesized on Ti electrodes

Thin films of polypyrrole, composited with poly(4-styrenesulfonate), formed electrochemically on titanium plate electrodes could be peeled off readily as free standing films, before and after reduction in the aqueous forming solution. Both surfaces (electrolyte side and electrode side) of such free standing films had been investigated using electron spectroscopy for chemical analysis (ESCA) and time of flight secondary ion mass spectrometry (TOF-SIMS). The morphologies for the electrolyte sides of both oxidized and reduced forms of such polypyrrole composite films were clearly different from those of the electrode sides, but little difference in surface conductivity between the two sides of each form was detectable using the four-point probe technique. ESCA spectra showed high sodium ion presence on the surfaces of the reduced form but not detectable on the surfaces of the oxidized form. Secondary electron images and ion maps of sampled areas on the films from the TOF-SIMS study revealed some interesting surface features.     

High contrast solid state electrochromic devices based on Ruthenium Purple nanocomposites fabricated by layer-by-layer assembly

Electrochromic Ruthenium Purple-polymer nanocomposite films, fabricated by multilayer assembly, were found to exhibit sub-second switching speed and the highest electrochromic contrast reported to date for any inorganic material.     

Poly(4-styrenesulfonate) templated polyaniline-carboxymethyl cellulose blend: Morphology and surface resistivity of the spin-coated films

Poly (4-styrenesulfonate) (PSS) templated polyaniline-carboxymethyl cellulose blend forming stable aqueous colloidal suspensions was prepared through simple synthesis. Morphology of the spin-coated films obtained from different concentrations of colloidal suspensions was studied through atomic force microscopy (AFM). The AFM images were found to be drastically altered at lower concentrations showing a regular network-like structure. Room-temperature surface resistivity for the network featured spin-coated film showed semiconducting behavior. This indicates the efficacy of dilution as a new design element for network structures, further exhibiting resistivity.     

Thermoresponsive polymeric nanoparticles based on poly(2‐oxazoline)s and tannic acid

Hydrogen bonding is widely present and plays a significant role in material science and supramolecular chemistry. This work reports a straightforward strategy for the preparation of polymeric nanoparticles from neutral poly(2‐oxazoline)s (POx) and tannic acid (TA) driven by their intermolecular hydrogen bonding. Dynamic light scattering (DLS) and scanning electron microscope (SEM) measurements showed that POx bearing different substituents, that is, methyl, ethyl and n‐propyl in the 2‐position all could assemble with TA into stable nanoparticles in water or ethanol. The diameter of the assembled nanoparticles could be manipulated by varying parameters such as molecular weight of POx, concentration and ratio of POx, and TA. Interestingly, POx/TA nanoparticles exhibited upper critical solution temperature (UCST)‐type thermoresponsive properties in ethanol or water depending on the molecular weight and substituent in the 2‐position of POx. Increasing or decreasing the temperature at the transition point resulted in the reversible transformation between assembled nanoparticles and disassembled poly(2‐n‐propyl‐2‐oxazoline) (PnPrOx) and TA. In view of the tailored size of the stable nanoparticles and the biocompatibilities of POx and TA, the prepared thermoresponsive nanoparticles are promising candidates as carriers for medicine toward related biomedical applications. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1520–1527     

Electrochemistry and electrochromic properties of phenanthroline-iron(II/III) complex films

New films of the iron complexes with bis((2-hydroxyphenyl)methylaminosulfonyl)bathophenanthroline(HPBP) and bis((2-aminophenyl)methylaminosulfonyl)bathophenanthroline(APBP) ligands are prepared on the electrode surfaces by electrochemical polymerization. The resulting film-coated electrode shows a well-defined reversible voltammogram corresponding to the redox reaction of the Fe(II/III) complexes and an electrochromic change from red(absorption maximum: 540 nm) to colorless. The response rate of the color change to a potential step was found to be correlated to the apparent diffusion coefficient(Dapp) for the homogeneous charge-transport process within the film. The Dapp values estimated are (3-4) × 10⁻⁹cm²s⁻¹ for the [Fe(APBP)₃] film and(1-2) × 10⁻⁸cm²s⁻² for the [Fe(HPBP)₃] film, respectively, by potential-step chronoamperometric and chronocoulometric methods. The result of electrochemical quartz crystal microbalance(EQCM) measurements⁴) and dependence of the formal potential of the metal complex of the Fe(II/III) redox couple with activity of the supporting electrolyte anion in NaClO₄ aqueous solution showed that anion, cation, and solvent move simultaneously across the polymer film/solution interface during the redox reaction. A piezoelectric admittance measurement⁴⁾ of the poly[Fe(APBP)₃] coated quartz crystal electrode showed that the viscosity of the film is affected by the oxidation state of iron.     

Aromatic-aromatic interaction between 2,3,5-triphenyl-2H-tetrazolium chloride and poly(sodium 4-styrenesulfonate)

Aromatic-aromatic interactions are found between the cationic molecule 2,3,5-triphenyl-2H-tetrazolium chloride (TTC) and the molecule poly(sodium 4-styrenesulfonate) (PSS) which makes the overall interaction of TTC with PSS more intense than the interaction with other polyanions containing sulfonate groups and produces a decrease on the redox ability of TTC. Diafiltration was used to compare the binding of TTC to PSS, poly(sodium vinylsulfonate) (PVS), and the more hydrophobic poly(sodium 2-(N-acrylamido)-2-methyl-propanesulfonate) (PAMPS). The UV-vis spectrum of TTC is changed in the presence of the aromatic polyanion. The 1H NMR signals of TTC are broadened and shifted in the presence of PSS, suggesting the occurrence of pi-pi interactions. Moreover, nuclear Overhauser effects (NOE) between the TTC and PSS protons are found. Possible structures for the complex are proposed.     

Electrochemical and electrochromic properties of layer-by-layer films from WO(3) and chitosan

The design of improved materials for electrochromic applications now involves extensive use of novel composites, thus requiring an investigation of the mechanisms responsible for electrochromism in these structures. Using films of WO(3) and chitosan produced with the layer-by-layer (LBL) technique, we demonstrate that characteristics such as the number of electrochemical active sites (K), the molar absorption coefficient (epsilon), and the electrochromic efficiency (eta) can be obtained using the quadratic logistic equation (QLE). The complexation ability between chitosan and WO(3) allowed the growth of visually uniform multilayers of the composite, with the same amount of material adsorbed in each deposition cycle. By fitting the absorbance changes (DeltaA) resulting from the electronic intervalence transfer from W(V) to W(VI) sites in four-bilayer LBL films of WO(3)/chitosan and WO(3)/chitosan with ethanol in the precursor dispersion, K was estimated to be ca. 5.5 x 10(-8) mol cm(-2) and 3.6 x 10(-8) mol cm(-2), respectively. The molar absorption coefficient and electrochromic efficiency vary with the charge injected because of the saturation of W(V) sites and the dissipation and feedback effects implicit in the QLE associated with ion-network interactions, such as the proton trapping effect. The LBL film of WO(3)/chitosan showed a smaller molar absorption coefficient and electrochromic efficiency than that containing ethanol because of a greater proton trapping effect for the LBL film with no ethanol. This enhanced trapping effect was seen as a decrease in the electronic flux involved in intervalence transfer in electrochemical impedance spectroscopy experiments.     

Synthesis and characterization of novel ion-imprinted polymeric nanoparticles for very fast and highly selective recognition of copper(II) ions

This work reports the preparation of new Cu²⁺ ion-imprinted polymeric nanoparticles using 1-hydroxy-4-(prop-2′-enyloxy)-9,10-anthraquinone (AQ) as a vinylated chelating agent. The Cu²⁺ ion found to form a stable 1:1 complex with AQ in methanol solution. The resulting Cu²⁺-AQ complex was copolymerized with ethyleneglycol dimethacrylate, as a cross-linking monomer, via precipitation polymerization method. The imprint copper ion was removed from the polymeric matrix using a 0.1 mol L⁻¹ HNO₃ solution. The Cu²⁺-imprinted polymeric nanoparticles were characterized by IR spectroscopy, scanning electron microscopy (SEM) and N₂ adsorption-desorption isotherms. The SEM micrographs showed colloidal nanoparticles of 60-100 nm in diameter and slightly irregular in shape. Optimum pH for maximum sorption was 7.0. Sorption and desorption of Cu²⁺ ion on the IIP nanoparticles were quite fast and achieved completely over entire investigated time periods of 2-30 min. Maximum sorbent capacity and enrichment factor of the prepared IIP for Cu²⁺ were 73.8 μmol g⁻¹ and 56.5, respectively. The relative standard deviation and limit of detection (C_LOD = 3S_b/m) of the method were evaluated as 2.6% and 0.1 ng mL⁻¹, using inductively coupled plasma-atomic emission spectrometry, respectively. It was found that the imprinting technology results in increased affinity of the prepared material toward Cu²⁺ ion over other metal ions with the same charge and close ionic radius. The relative standard deviations for six and twenty replicates with the same nanoparticles were found to be 1.7% and 2.1%, respectively.     

Three colour electrochromic metallopolymer based on a ruthenium phenolate complex bound to poly(4-vinyl)pyridine

The photonic and electrochemical properties of a novel Ru–phenolate based metallopolymer are reported. The complex undergoes a ruthenium based reversible oxidation at approximately +0.400 V and irreversible box ligand oxidation at +0.800 V vs. Ag/AgCl. Oxidation of thin films in aqueous electrolyte at +0.500 V reversibly switches the colour from wine red to light green and a red orange colour is observed for mixed redox composition. In contrast, oxidation at potentials more positive than +1.500 V shows no visible colour change but produces a change in the near infra-red region. To determine the electrochromic switching rate and to identify the rate determining step of the, scan rate dependent cyclic voltammetry was performed under semi-infinite linear diffusion conditions in aqueous lithium perchlorate. These data reveal that the homogeneous charge transport diffusion coefficient, D_CT, is 3.6 ± 0.2 × 10⁻¹³ cm² s⁻¹, i.e., under these conditions it takes approximately 90 s to fully oxidise a 100 nm thick film.     

Complex formation between rhodamine B and poly(sodium 4-styrenesulfonate) studied by 1H-NMR

A 1H NMR study is presented for the binding of rhodamine B (RB) to the polyanion containing aromatic groups poly(sodium 4-styrenesulfonate) (PSS), which is also evidenced by diafiltration. 1H NMR spectra showed an accentuated upfield shift of proton H6' of the benzoic ring of RB at pH 7, indicating the stacking of RB onto PSS. The corresponding structure is proposed which is in accordance to Hunter and Sanders rules. At pH 2, an upfield shift of the xanthene protons of RB would indicate a highly condensed state for this molecule.     

The synthesis of poly(3,4-dihydroxystyrene) and poly[(sodium 4-styrenesulfonate)-co-(3,4-dihydroxystyrene)]

Poly(2-methoxy-4-vinylphenol), polyMVP, and poly[(sodium 4-styrenesulfonate)-co-(2-methoxy-4-vinylphenol)], poly(SSS/MVP), were synthesized by radical polymerization using Vazo-64 or tributylborane as initiator. Poly(3,4-dihydroxystyrene) and poly[(sodium 4-styrenesulfonate)-co-(3,4-dihydroxystyrene)] were obtained by demethylation of polyMVP and poly(SSS/MVP) using HBr and trimethylsilyl iodide, respectively. (Co)polymer structures were confirmed by ¹H and ¹³C NMR spectra. About 30 wt.-% gel formed in the polyMVP polymerizations, whereas only a small amount (0.5 mol-%) of gel formed in the copolymerizations.     

pH dependence of the interaction between rhodamine B and the water-soluble poly(sodium 4-styrenesulfonate)

The binding of rhodamine B (RB) to the polyanion containing aromatic groups poly(sodium 4-styrenesulfonate) (PSS) is studied by separation and spectroscopic techniques at pH between 2 and 7. Significant binding is found at pH below 5, together with a red-shift of the RB maximum of absorbance to 564 nm, and RB fluorescence quenching. The dependence of the pH is related with protonation of RB molecules. Fluorescence quenching is a consequence of a more hydrophobic environment and may occur on territorially or site-specifically bound molecules, and/or on self-aggregated molecules in a hydrophobic polymer domain. Remarkably, the basicity of RB is increased by the influence of the polymer.     

Creatinine sorbents based on nonwoven polymeric materials modified with tetra(4-tert-butyl)phthalocyanine and zinc complex

The experimental results, which show the possibility of immobilization of tetra(4-tert-butyl)phthalocyanine complex and its zinc complex on the surface of nonwoven polypropylene and lavsan materials. The alkali etching method was used for activation of the polypropylene surface. It was shown that the modified polymeric materials possess sorption activity relative to creatinine.     

Metallopolymeric films based on a biscyclometalated ruthenium complex bridged by 1,3,6,8-tetra(2-pyridyl)pyrene: applications in near-infrared electrochromic windows

A biscyclometalated ruthenium complex bridged by the 2,7-deprotonated form of 1,3,6,8-tetra(2-pyridyl)pyrene was deposited onto indium-tin oxide glass electrodes by reductive electropolymerization. The resulting metallopolymeric films exhibited tricolor electrochromic behavior in the near-infrared region upon switching of the two well-separated Ru(II/III) processes at low potentials. A good contrast ratio (35%) at 2050 nm and a long memory time up to 100 min were recorded for this electrochromic behavior. The response time is typically of a few seconds.