Fabrication and Properties of Conducting Polypyrrole/SWNT‐PABS Composite Films and Nanotubes

We report the electropolymerization and characterization of polypyrrole films doped with poly(m‐aminobenzene sulfonic acid (PABS) functionalized single‐walled nanotubes (SWNT) (PPy/SWNT‐PABS). The negatively charged water‐soluble SWNT‐PABS served as anionic dopant during the electropolymerization to synthesize PPy/SWNT‐PABS composite films. The synthetic, morphological and electrical properties of PPy/SWNT‐PABS films and chloride doped polypyrrole (PPy/Cl) films were compared. Characterization was performed by cyclic voltammetry, atomic force microscopy (AFM), scanning electron microscopy (SEM) and Raman spectroscopy. SEM and AFM images revealed that the incorporation of SWNT‐PABS significantly altered the morphology of the PPy. Cyclic voltammetry showed improved electrochemical properties of PPy/SWNT‐PABS films as compared to PPy/Cl films. Raman Spectroscopy confirmed the presence of SWNT‐PABS within composite films. Field effect transistor (FET) and electrical characterization studies show that the incorporation of the SWNT‐PABS increased the electronic performance of PPy/SWNT‐PABS films when compared to PPy/Cl films. Finally, we fabricated PPy/SWNT‐PABS nanotubes which may lead to potential applications to sensors and other electronic devices.     

Electronic and optical properties of pyrrole and thiophene oligomers: A density functional theory study

The conductive mechanism of pyrrole (Py) and thiophene (Th) oligomers is investigated in the framework of density functional theory. Geometric constructions and electronic structures of neutral n‐Py/n‐Th and oxidized n‐Py^m+/n‐Th^m+ oligomers (6 ≤ n ≤ 48, 2 ≤ m ≤ 18) are reported as a function of oligomer length. The charges in the oxidized oligomers have a localized distribution along the oxidized n‐Py^m+/n‐Th^m+ oligomers, and each set of two positive charges is localized in one area. Therefore, the charge carriers in oxidized n‐Py^m+/n‐Th^m+ oligomers are bipolarons. Furthermore, the nonlinear optical properties of the n‐Py/n‐Th oligomers are investigated, for which the static polarizability α, the first polarizability β, and the second polarizability γ are calculated. When the ratio of m/n is 1/3, the static polarizability <α> and the polarizability anisotropy Δα are maximized. In addition, neutral n‐Py/n‐Th oligomers have maximum <γ> values. The values of β were determined mainly by the dipole of the molecule, while the values of γ were closely related to the aromaticity of the oligomer. The stronger the aromaticity, the bigger the γ value. All calculations indicate that the polarizability and absorption spectrum can be tuned by controlling the oxidation level, making these oligomers applicable as good nonlinear optical materials.     

Dopant effect and characterization of polypyrrole-cellulose composites prepared by in situ polymerization process

Polypyrrole (PPy)-cellulose composites were prepared by in situ polymerization of pyrrole in pulp suspension using ferric chloride as an oxidant. Some sulfonic compounds including p-toluenesulfonic acid and its sodium salt (PTSA and PTSA-Na), benzenesulfonic acid (BSA), dodecylbenzene sulfonic acid and its sodium salt (DBSA and DBSA-Na), 2-naphthalene sulfonic acid (NSA) and 9,10-anthraquinone-2-sulfonic acid sodium salt (AQSA-Na) were used as dopants, and their effect on the conductivity of PPy-cellulose composite was investigated. The results showed that the species and dose of dopants had significant effect on the surface resistivity and environmental stability of PPy-cellulose composite. As the dopant, PTSA and DBSA had a superior doping effect compared to their sodium salts. The doping result of BSA was close to that of PTSA. NSA bearing a naphthalene ring and AQSA-Na bearing an anthraquinone ring gave the best conductivity. Using NSA or AQSA-Na as a dopant, along with suitable polymerization conditions, the PPy-cellulose composite obtained showed a surface resistivity as low as 20 Ω cm⁻². For most dopants, the lowest surface resistivity could be obtained when the molar ratio of dopant to pyrrole was 1:1. Both ATR-FTIR (attenuated total reflection-Fourier transform infrared spectroscopy) and XPS (X-ray photoelectron spectroscopy) analysis confirmed that the PPy on pulp fibers doped with PTSA, PTSA-Na, NSA and AQSA-Na had different doping levels. The higher doping level of the PPy in the composites doped with NAS and AQSA-Na might be related to the stronger interaction of cellulose with PPy chains. Both SEM (scanning electron microscopy) and AFM (atomic force microscopy) observation revealed the fine grain microstructure of the PPy on the composites with average grain sizes in the range of 100–200 nm, and the PPy on the samples doped with NSA and AQSA-Na exhibited quite different morphology as compared to those doped with PTSA and its sodium salt.     

Potentiometric Ag+ Sensors Based on Conducting Polymers: A Comparison between Poly(3,4‐ethylenedioxythiophene) and Polypyrrole Doped with Sulfonated Calixarenes

Potentiometric Ag⁺ sensors were prepared by galvanostatic electropolymerization of 3,4‐ethylenedioxythiophene (EDOT) and pyrrole (Py) on glassy carbon electrodes by using sulfonated calixarenes as doping ions. Poly(3,4‐ethylenedioxythiophene) (PEDOT) and polypyrrole (PPy) doped with p‐sulfonic calix[4]arene (C4S), p‐sulfonic calix[6]arene (C6S) and p‐sulfonic calix[8]arene (C8S) were compared. PEDOT and PPy doped with poly(styrene sulfonate) (PSS) were also included for comparison. The analytical performance of the conducting polymer‐based Ag⁺ sensors was studied by potentiometric measurements. All conducting polymer and dopant combinations showed sensitivity and selectivity to Ag⁺ compared to several alkali, alkaline‐earth, and transition‐metal cations. The type of the conducting polymer used for the fabrication of the electrodes was found to have a more significant effect on the selectivity of the electrodes to Ag⁺ than the ring size of the sulfonated calixarenes used as dopants. Selected conducting polymer‐based sensors were studied by cyclic voltammetry (CV) and energy dispersive analysis of X‐rays (EDAX) measurements. Results from the EDAX measurements show that both PEDOT‐ and PPy‐based membranes accumulate silver.     

Polypyrrole/poly(N‐isopropylacrylamide‐co‐acrylic acid) thermosensitive and electrically conductive composite microgels

The electrically conductive polypyrrole/dodecylbenzene sulfonic acid/poly(N‐isopropylacrylamide‐co‐acrylic acid) (PPy/DBSA/poly(NIPAAm‐co‐AA)) composite microgels were synthesized by a chemical oxidation of pyrrole in the presence of DBSA as the primary dopant, and poly(NIPAAm‐co‐AA) microgels as the polymeric codopant and template, in which APS was used as the oxidant. It was proposed to prepare “intelligent” polymer microgel particles containing both thermosensitive and electrically conducting properties. The polymerization of pyrrole took place directly inside the microgel networks, leading to formation of composite microgels and the morphology was observed by transmission electron microscope. PPy particles interacted strongly with microgels, as the acid groups of microgels acted as the polymeric codopant. The composite microgels thus formed showed electrically conducting behavior dependent on humidity and temperature. At temperatures lower than lower critical solution temperature, the conductivity decreased with increasing the humidity and a small hysteresis phenomenon was observed. The hysteresis became indistinct when temperature was near volume phase transition temperature. However, after the treatment of high temperature and high humidity, the conductivity increased surprisingly due to the structure reorganization inside the composite microgels. The distinctive functionality of the PPy composite microgels was expected to be utilized in many attractive applications. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1648–1659, 2006     

Characterization of Conducting Copolymer of Pyrrole via Pyrolysis Mass Spectrometry

In this work, structural and thermal characterization of BF₄ ^? doped copolymer of pyrrole (PPy) with 2‐methylbutyl‐2‐(3‐thienyl)acetate prepared by electrochemical polymerization were performed via a pyrolysis mass spectrometry technique. The pyrolysis mass spectrometry data of the copolymer PPy/PMBTA, and the homopolymers; polypyrrole, PPy, and poly(2‐methylbutyl‐2‐(3‐thienyl)acetate), PMBTA were analyzed and compared. It has been determined that when the electrochemical polymerization of pyrrole was achieved on a PMBTA coated anode through the thiophene moieties of PMBTA, thermal stability of PMBTA chains increased slightly and the decomposition of both units followed quite similar pathways indicating an increase in the thermal stability of PMBTA chains unlike what was observed for PTSA doped PPy/PMBTA copolymer.     

Theoretical study on the interaction of neutral and charged Tin (n = 1–7) clusters with one oxygen molecule

The interactions between the neutral and charged (?2, ?1, +1, and +2) Ti_n (n = 1–7) clusters and one O₂ molecule were investigated by density functional theory. The calculated results show that the oxygen molecule is dissociative on the neutral Ti_n clusters. Geometrically, the two O atoms are distributed at the two sides across the neutral Ti_n cluster for n = 1–4 and the oxygen atom favors the three‐fold hollow site for n = 5, 6, and 7. The binding energy per atom (E_b) and energy gap (E_gap) show higher stability and lower chemical activity of the neutral Ti_nO₂ (n = 1–7) systems compared with the corresponding Ti_n clusters. The adsorption energies (E_ad) exhibit a continuously ascending tendency except for n = 4. The results of the addition of different charges (?2, ?1, +1, and +2) on the most stable neutral Ti_nO₂ (n = 1–7) systems indicate that their geometries are usually perturbed. The stabilities of the neutral Ti_nO₂ systems are enhanced by adding one negative charge. The strongest interaction of the charged Ti_n clusters (?2, ?1, +1, and +2) with O₂ molecule is found at charge +2. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Intermolecular interactions of a size‐expanded guanine analogue with gold nanoclusters

The interactions between a size‐expanded Guanine analogue x‐Guanine (xG) and gold nanoclusters, Au_n (n = 2, 4, 6, and 8), were studied theoretically using density functional theory. Geometries of neutral complexes were optimized using the B3LYP functional with the 6‐31+G(d,p) basis set for xG and the LANL2DZ basis set for gold clusters. The binding modes, interaction strength, and the charge‐transfer properties of different Au_n‐xG complexes were investigated. Natural population analysis was performed for natural bond order charges. It was found that gold nanoclusters form stable complexes with xG and these binding results in a substantial amount of electronic charge being transferred from xG to the gold clusters. The vertical first ionization potential, electron affinity, Fermi Level, and the HOMO–LUMO gap of xG and its complexes with gold nanoclusters were also analyzed. © 2013 Wiley Periodicals, Inc.     

Time‐dependent density functional theory study on direction‐dependent electron and hole transfer processes in molecular systems

We report on real‐time time‐dependent density functional theory calculations on direction‐dependent electron and hole transfer processes in molecular systems. As a model system, we focus on α‐sulfur. It is shown that time scale of the electron transfer process from a negatively charged S₈ molecule to a neighboring neutral monomer is comparable to that of a strong infrared‐active molecular vibrations of the dimer with one negatively charged monomer. This results in a strong coupling between the electrons and the nuclei motion which eventually leads to S₈ ring opening before the electron transfer process is completed. The open‐ring structure is found to be stable. The similar infrared‐active peak in the case of hole transfer, however, is shown to be very weak and hence no significant scattering by the nuclei is possible. The presented approach to study the charge transfer processes in sulfur has direct applications in the increasingly growing research field of charge transport in molecular systems. © 2017 Wiley Periodicals, Inc.     

The Interplay Between Lead Vacancy and Water Rationalizes the Puzzle of Charge Carrier Lifetimes in CH3NH3PbI3: Time‐Domain Ab Initio Analysis

The perovskite CH₃NH₃PbI₃ excited‐state lifetimes exhibit conflicting experimental results under humid environments. Using ab initio nonadiabatic (NA) molecular dynamics, we demonstrate that the interplay between lead vacancy and water can rationalize the puzzle. The lead vacancy reduces NA coupling by localizing holes, slowing electron–hole recombination. By creating a deep electron trap state, the coexistence of a neutral lead vacancy and water molecules enhances NA coupling, accelerating charge recombination by a factor of over 3. By eliminating the mid‐gap state by accepting two photoexcited electrons, the negatively charged lead vacancy interacting with water molecules increases the carrier lifetime over 2 times longer than in the pristine system. The simulations rationalize the positive and negative effects of water on the solar cell performance exposure to humidity.     

Exploring the electro‐optical properties of conjugated polymers based on oligo‐selenophene and oligo(3,4‐ethylenedioxyselenophene)

For seeking high‐efficiency narrow‐band‐gap donor materials to enhance short‐circuit current density for organic solar cells, a series of oligo‐selenophene (OS) and oligo(3,4‐ethylenedioxyselenophene) (OEDOS) with various chain lengths were designed and characterized using density functional theory (DFT) and time‐dependent DFT calculations. Based on the results, it can be seen that with increasing chain length of the oligomers in both syn‐ and anti‐adding manners, the bond length alternation is decreased which indicates that the π‐electron delocalization is increased. Also, when the chain length is increased the electronic energy gap and the optical energy gap are decreased. It can be concluded that the syn‐(OS)_n=10,14,15, anti‐(OS)_n=14 and anti‐(OEDOS)_n=7–12 oligomers can act as low‐band‐gap polymers. Therefore they can absorb more sunlight based on maximum wavelength (higher than 620 nm). Furthermore, a red shift in the simulated absorption spectra of (OS)_n and (OEDOS)_n donors is observed. It is found that (OS)_n=14,15 with syn configuration of the extended oligomers is the most suitable donor for the design of high‐performance organic solar cells possessing a narrow electronic band gap, high exciton lifetime and broad and intense absorption spectra that cover the solar spectrum leading to complete light‐harvesting efficiency.     

Theoretical study of the effect of counterions on the structure of pyrrole oligomers

The influence of counterions on the calculated properties of positively charged pyrrole oligomers is studied using the semiempirical AM1 and PM3 methods. The geometry and properties of the charged pyrrole oligomers are significantly affected by counteranions both in anti and syn conformations. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem 88: 296–301, 2002     

Retention Behavior of Neutral and Positively and Negatively Charged Solutes on an Immobilized‐Artificial‐Membrane (IAM) Stationary Phase

The retention behavior of neutral, positively charged, and negatively charged solutes on the IAM.PC.DD2 stationary phase was investigated and compared. A set of monofunctional compounds and complex drugs (steroids, nonsteroidal anti‐inflammatory drugs, and β‐blockers) were selected for this study, i.e., neutral solutes and solutes with acidic or basic functionalities which are positively charged or negatively charged at pH 7.0. The correlation between the retention factor log k_w at pH 7.0 on the IAM.PC.DD2 stationary phase and the partition coefficient log P_oct or the distribution coefficient log D_7.0 showed that the retention mechanism depends on the charge state and structural characteristics of the compounds. The neutrals were least retained on the IAM.PC.DD2 stationary phase, and positively charged solutes were more retained than negatively charged ones. This implies that the retention of the charged solutes is controlled not only by lipophilicity but also by the electrostatic interaction with the phospholipid, with which positively charged solutes interact more strongly than negatively charged ones.     

Synthesis of polypyrrole micro/nanofibers via a self-assembly process

Novel polypyrrole (PPy) micro/nanofibers were synthesized via a self-assembly process by using 4-hydroxy-3-[(4-sulfo-1-naphthalenyl) azo]-1-naphthalenesulfonic acid (Acid Red B) as dopant and ferric chloride (FeCl₃) as oxidant. Experimental conditions, including the concentration of the dopant, reaction temperature and stirring state have been investigated for their influences on the morphology of the synthesized PPy micro/nanofibers. The products were characterized by scanning electron microscopy, transmission electron microscopy and Fourier-transform infrared spectroscopy. The formation mechanism of micro/nanofibers was studied. It is believed that the micelles formed by the dopant and pyrrole monomer act as templates during the synthesis process. Two functions of aggregation and synthesis are proposed in the reaction system simultaneously, and the morphologies of micro/nanofibers are the co-operations of these two functions. The maximum conductivity value of the PPy micro/nanofibers was 8.56 S cm^?1     

Synthesis and in situ doping of highly conductive polypyrrole nanocomplexes with binary acids

The synthesis of doped polypyrrole (PPy) nanocomplexes and their size, morphology, doping level, and electrical conductivity are discussed. The synthetic route of doped PPy nanocomplexes is presented by means of the chemical oxidative polymerization and in situ doping process in the presence of a binary acid mixture (hydrochloric acid and perchloric acid). The electrical conductivities of the doped PPy nanocomplexes are enhanced from 0.88 to 4.5 S/cm by the optimum molar ratio of HClO₄ and HCl in the binary acid mixture. In addition, the average particle size of the doped PPy nanocomplexes decreases from 280 to 30 nm with a narrow particle size distribution when increasing the proportion of HClO₄ relative to HCl in the binary acid mixture; this result is confirmed by scanning electron microscopy, transmission electron microscopy, and capillary hydrodynamic fractionation instrument analyses. Moreover, at different molar ratios in the binary acid mixture, the zeta‐potential and oxidation level of the doped PPy nanocomplexes have a confirmed association with particle size and electrical properties. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2329–2336     

Novel pH‐responsive mixed‐charge copolymer brushes based on carboxylic acid and quaternary amine monomers

In this study, we report on the fabrication of tunable mixed‐charged copolymer brushes consisting of negatively charged carboxylic acid monomer (4‐vinylbenzoic acid, VBA) and positively charged quaternary amine monomer ((ar‐vinylbenzyl)trimethylammonium chloride) via reversible addition–fragmentation chain transfer‐mediated polymerization. The copolymer brushes have negative charge under neutral and basic conditions, and are positively charged under acidic conditions owing to the protonation of the carboxylate groups. The copolymer brushes revealed a unique reversible wetting behavior with pH. The reversible properties of the copolymer brushes can be employed to regulate the adsorption of charged biomacromolecules such as DNA and proteins. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Ab initio molecular orbital theory study of GaAs clusters: The geometry

We have studied the structure and geometry of neutral and charged atomic clusters consisting of Ga and As atoms via ab initio Hartree–Fock (HF) and second‐order Møller–Plesset methods. The Ga_mAs_n cluster with m≠n composition prefers a nontetrahedral geometry in the charge neutral (q=0) state. These clusters tend to be stable in tetrahedral geometry when appropriately charged. The Ga_mAs_n cluster with m=n composition (1:1 ratio of Ga to As atoms) tends to be stable in a tetrahedral geometry in the charge neutral (q=0) state. With increasing size of the cluster, the geometry of Ga_nAs_n cluster approaches the zinc‐belende‐type crystalline structure. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 77: 563–573, 2000     

Synthesis and characterization of polypyrrole nanofibers with different dopants

Nanostructures of polypyrrole (PPy) were synthesized in the presence of different dopants including hydrochloric acid (HCl), ferric chloride (FeCl₃), p‐toluene sulfonic acid (p‐TSA), camphor sulfonic acid (CSA), and polystyrene sulfonic acid (PSSA), using a simple interfacial oxidative polymerization method. The method is a reliable non‐template approach with relatively simple instrumentation, ease of synthesis, and economic viability for synthesizing PPy nanostructures. Morphology of synthesized PPy structures was investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which indicate the formation of one‐dimensional (1D) nanofibers with average diameter of 75–180 nm. Energy dispersive spectrum (EDS) of the PPy nanofibers indicates the attachment of the dopants to the PPy backbone; the fact is further confirmed by the Fourier transform infrared (FTIR) spectra of PPy nanostructures. Thermal stabilities of the nanostructures explored using thermal gravimetric analysis (TGA) follow the order PPy‐p‐TSA > CSA > HCl > FeCl₃ > PSSA. It is noticed that the electrical conductivity (EC) of PPy nanostructures depends upon the nature of dopant (PPy‐p‐TSA > CSA > HCl > FeCl₃ > PSSA), PPy‐p‐TSA nanofibers showing the highest EC of 6 × 10^?2 Scm^?1. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of Polypyrrole Microtubes with Actinomorphic Morphology in the Presence of a β‐Cyclodextrin Derivative‐Methyl Orange Inclusion Complex

Summary: Polypyrrole (PPy) microtubes with an actinomorphic morphology are synthesized by a chemical method in the presence of an inclusion complex (IC) of mono [6‐deoxy‐6‐(2‐butenedinitrile‐2,3‐dimercapto sodium salt)]‐β‐cyclodextrin (6‐mnt‐β‐CD) with methyl orange (MO) as a dopant in aqueous solution. The morphologies of the obtained PPy were studied using transmission electron microscopy (TEM). It was found that the IC of 6‐mnt‐β‐CD with MO significantly affects the morphology of the resulting PPy.

The morphology of polypyrrole synthesized in the presence of 6‐mnt‐β‐CD/MO, determined by TEM.     

Highly Sensitive Functionalized Conducting Copolypyrrole Film for DNA Sensing and Protein‐resistant

In order to exploit the applications of polypyrrole (PPy) derivatives in biosensors and bioelectronics, the different immobilization mechanisms of biomolecules onto differently functionalized conducting PPy films are investigated. Pyrrole and pyrrole derivatives with carboxyl and amino groups were copolymerized with ω‐(N‐pyrrolyl)‐octylthiol self‐assembled on Au surface by the method of the chemical polymerization to form a layer of the copolymer film, i.e., poly[pyrrole‐co‐(N‐pyrrolyl)‐caproic acid] (poly(Py‐co‐PyCA)) and poly[pyrrole‐co‐(N‐pyrrolyl)‐hexylamine] (poly(Py‐co‐PyHA)), in which the carboxyl groups in poly(Py‐co‐PyCA) were activated to the ester groups. Based on the structure characteristics, the immobilization/hybridization of DNA molecules on PPy, poly(Py‐co‐PyCA) and poly(Py‐co‐PyHA) were surveyed by cyclic voltammograms measurements. For differently functionalized copolymers, the immobilization mechanisms of DNA are various. Besides the electrochemical properties of the composite electrodes of PPy and its copolymers being detected before and after bovine serum albumin (BSA) adsorption, the kinetic process of protein binding was determined by surface plasmon resonance of spectroscopy. Since few BSA molecules could anchor onto the PPy and its copolymers surfaces, it suggests this kind of conducting polymers can be applied as the protein‐resistant material.