Influence of counter ion on polyaniline and polypyrrole

The electronic, magnetic, optical and redox properties of conjugated polymers are greatly influenced by structure, electronegativity, solvation and orientation of a counter ion. The doping by counter ion not only creates a band structure but also stabilizes localized bound states to impart unusual optical and magnetic properties to macromolecular system. When the polymer is in contact with solution of an electrolyte, counter ion tends to be solvated and mobile in the polymer phase, imparting it a property of ion exchange membrane. Here we briefly summarize the influence of anion on properties and electrochemical behaviour of polyaniline and polypyrrole.     

Conjugated polymers as robust carriers for controlled delivery of anti-inflammatory drugs

Conjugated polymers due to their reversible transition between the redox states are potentially able to immobilise and release ionic species. In this study, we have successfully developed a conducting polymer system based on poly(3,4-ethylenedioxythiophene) (PEDOT) for electrically triggered, local delivery of an ionic form of ibuprofen (IBU), a non-steroidal anti-inflammatory, and analgesic drug. It was shown that by changing the electropolymerisation conditions, the polymer matrix of specified IBU content can be synthesised. The electrochemical synthesis has been optimised to obtain the conducting matrix with the highest possible drug content. The process of electrically stimulated drug release has been extensively studied in terms of the dynamics of the controlled IBU release under varying conditions. The maximum concentration of the released IBU, 0.66 (±0.10) mM, was observed at the applied potential E = ?0.5 V (vs. Ag/AgCl). It was demonstrated that the immobilisation-release procedure can be repeated several times making the PEDOT matrix promising materials for controlled drug release systems applied e.g. in neuroprosthetics.     

Time-Resolved Structural Kinetics of an Organic Mixed Ionic–Electronic Conductor

The structure and packing of organic mixed ionic–electronic conductors have an especially significant effect on transport properties. In operating devices, this structure is not fixed but is responsive to changes in electrochemical potential, ion intercalation, and solvent swelling. Toward this end, the steady-state and transient structure of the model organic mixed conductor, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), is characterized using multimodal time-resolved operando techniques. Steady-state operando X-ray scattering reveals a doping-induced lamellar expansion of 1.6 Å followed by 0.4 Å relaxation at high doping levels. Time-resolved operando X-ray scattering reveals asymmetric rates of lamellar structural change during doping and dedoping that do not directly depend on potential or charging transients. Time-resolved spectroscopy establishes a link between structural transients and the complex kinetics of electronic charge carrier subpopulations, in particular the polaron–bipolaron equilibrium. These findings provide insight into the factors limiting the response time of organic mixed-conductor-based devices, and present the first real-time observation of the structural changes during doping and dedoping of a conjugated polymer system via X-ray scattering.     

Stability and behavior of poly-1-naphthol films towards charge transfer reactions

Conducting poly-1-naphthol films (0.5–2.0 μm) showed a decreasing tendency for doping with film thickness. The average specific capacitance of poly-1-naphthol films formed by cyclic voltammetry in MeCN containing tetrabutylammonium perchlorate in the reduced dedoped state was found to be 10 mF cm⁻³ and increased on electrochemical oxidation (doping) to 60 mF cm⁻³. Stabilization of the polymer by repetitive cyclic voltammetry led to increase or decrease in the redox charge with number of cycles, depending on the final oxidation potential and in all cases, the peak separation decreased due to rearrangement of the polymer chains. The polymer doping/dedoping processes showed a pronounced increase in the diffusion coefficient of the charge transfer with thickness and a substantial difference between the doping and dedoping process. The doping process is controlled by an initial fast charge propagation step and followed by a slower step of anion insertion into the polymer film while in the dedoping only the anion removal from the film could be distinguished. The electron transfer for the redox [Fe(CN)₆]^4−/3− on the polymer films showed also a strong dependence on film thickness. It is inferred that the polymer film is composed of two layers; an inner compact layer (< 1 μm) which impedes to a larger extent the charge transfer reactions and an outer less compact and easily removable layer with more facile permeability. When the film is thickened, however, the inner layer is partially distorted and its barrier character towards charge transfer is gradually lost.     

Tailoring the optoelectronic properties of donor-acceptor-donor type π-conjugated polymers via incorporating different electron-acceptor moieties

Syntheses of donor-acceptor-donor type of π-conjugated monomers were performed to examine the effect of the acceptor units' strength on the electrochemical and optoelectrochemical properties of the resulting monomer and polymer. Palladium catalyzed Stille cross-coupling reaction of an organotin reagent with an organic electrophile was used for the synthesis of target monomers, 5,8-bis(4-hexylthiophen-2-yl)-2-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-3-(2,3-dihydrobenzo[b][1,4]dioxin-7-yl)quinoxaline (DBQHT) and 10,13-bis(4-hexylthiophen-2-yl)dibenzo[a,c]phenazine (PHEHT).The presence of the strong electron-donating ethylenedioxy groups on pendant phenyl rings increased electron density on DBQHT, thus the oxidation potential of DBQHT shifts to a lower value than that of PHEHT. The π-π* absorption maximum of PPHEHT was about 40 nm red-shifted compare to that of PDBQHT, which can be attributed to the increase of the effective conjugation and coplanarity of PPHEHT relative to PDBQHT via using phenanthrene fused quinoxaline unit as the acceptor. The electronic band gap of polymer, defined as the onset of the π-π* transition, is found to be 1.65 eV for PPHEHT and 1.82 eV for PDBQHT. Both polymer films showed multi-color electrochromism. PDBQHT can be switched between a red neutral state and a green oxidized state with two intermediate states; purple and brown. PPHEHT also shows multicolored electrochromic behavior with three distinct states: a blue neutral state, a gray intermediate state, and a green oxidized state.     

Electrochromic thin films from a redox active diarylethene by electrochemical polymerization

A diarylethene substituted with 3,4-(propane-1,3-diyldioxy)thiophene (ProDOT) was synthesized to induce electrochemical deposition of diarylethenes. The ProDOT substituted diarylethene (BTFPP) showed reversible photochromism from colorless to purple upon exposure to a UV light and bleached to colorless by a visibly light. The oxidation potential of the new ProDOT substituted diarylethene was lower than that of the unsubstituted diarylethenes due to the electroactive ProDOT unit. Under an electrochemical condition, the solution of BTFPP gave soluble polymers but deposited insoluble film on a working electrode coated with a PEDOT layer. This result indicates that the PEDOT nano layer (68 nm thick) function as a seeding layer to induce polymerization and electrodeposition of BTFPP. Furthermore electro-copolymerization using a mixture of BTFPP and EDOT afforded electrodeposition of the copolymers on the PEDOT seeding layer. An electrochromic electrode was successfully fabricated by depositing the photochromic BTFPP on an ITO glass, which shows a reversible electrochromic change from violet to sky blue.     

Color combination of conductive polymers for black electrochromism

Conducting polymers that absorb three primary colors, red, green, and blue (RGB), were introduced with a yellow electrochromic polymer (Y) for the preparation of black electrochromic devices. Red poly(3-hexylthiophene) (P3HT) and blue poly(3,4-ethylenedioxythiophene) (PEDOT) were coated on one side of the electrode as a cathodically coloring electrochromic (EC) layer, while green poly(aniline-N-butylsulfonate) (PANBS) and yellow EC poly{[1,3-bis(9',9'-dihexylfluoren-20-yl)azulenyl]-alt-[2",7"-(9",9"-dihexylfluorenyl]} (PDHFA) were coated on the opposite electrode to complete a complementary EC device. The yellow PDHFA layer effectively compensated for absorption below 450 nm and above the 600 nm region, which was lacking in the RGB electrode. The resultant RGBY ECD provided a black color near the CIE black with L*, a*, and b* values of 32, -1.1, and 3.7, respectively, covering a broad absorption in the visible range in the colored state. The state of the black EC device was maintained, even after the electricity was turned off for 200 h, showing stable memory effect.     

Combined electrochromic and plasmonic optical responses in conducting polymer/metal nanoparticle films

Poly(3,4-ethylenedioxithiophene)/poly(styrene sulphonate) (PEDOT/PSS) aqueous dispersions were mixed with aqueous gold nanoparticle and aqueous silver nanoparticle colloids. PEDOT/gold nanoparticles (Au NP) and PEDOT/silver nanoparticles (Ag NP) films were obtained by solvent casting the corresponding aqueous solutions. The nanocomposite films showed the optical characteristics associated with both the surface plasmon absorption resonance of the metal nanoparticles and the excitation of the bipolaron band of the conducting polymer. As an interesting application we demonstrate the use of metal nanoparticles to tune the color of PEDOT based electrochromic films from blue to violet in the case of Au NP or green in the case of Ag NP.     

Controlled doping of double walled carbon nanotubes and conducting polymers in a composite: An in situ Raman spectroelectrochemical study

The interaction of double wall carbon nanotubes (DWCNTs) and the conducting polymer poly(3,4-ethylenedioxythiphene)/polystyrenesulfonate (PEDOT/PSS) was studied by in-situ Raman spectroelectrochemistry. The mixing of DWCNTs with PEDOT/PSS caused a partial doping of the outer tube of DWCNTs, which was indicated by the relative change of the Raman intensity of the DWCNTs features. On the other hand, the bands corresponding to inner tubes of DWCNTs and to the polymer were almost untouched by assembling both species into a composite. The in-situ Raman spectroelectrochemical experiments have shown that the changes in electronic structure of inner tubes of DWCNTs embedded in PEDOT/PSS matrix are dependent on the doping level. While at the low doping level of the composite, the Raman features of inner tubes of DWCNTs do not change significantly, at high doping level they reflect the changes caused by the applied electrochemical potential similar to those observed in the polymer-free DWCNTs.     

Construction of electrochromic devices using thiophene based conducting polymers

Dual type polymer electrochromic devices (ECDs) based on poly(terepthalic acid bis-(2-thiophen-3-yl-ethyl)ester) (PTATE), its copolymer with thiophene P(TATE-co-Th) and poly(3,4-ethylenedioxythiophene) (PEDOT) have been constructed. Spectroelectrochemistry, switching ability and stability of the devices were investigated by UV-Vis Spectrophotometer and Cyclic voltammetry. These devices exhibit low switching voltages (between 0.0 V and +1.6 V), short switching times with reasonable switching stability under atmospheric conditions.     

新型多功能无机/有机复合薄膜的制备及电化学性能研究

将铈钛氧簇[Ti₈O₇(HOEt)(OEt)₂₁Ce]和PEDOT低聚物的混合溶液通过滴涂-二次聚合成膜制得一种表面具有特殊纳米沟壑结构的无机/有机复合薄膜PEDOT:Ce@TiO₂。PEDOT:Ce@TiO₂具有很强的疏水性和对乙腈溶液较好的润湿性, 能用作阴极电致变色材料和超级电容器电极材料。PEDOT:Ce@TiO₂展现出较PEDOT薄膜更优良的电化学性能, 在电流密度为1 A/g时, PEDOT:Ce@TiO₂的质量比电容为71.2 F/g, 是相同条件下PEDOT薄膜的质量比电容的1.7倍。采用PEDOT:Ce@TiO₂进一步组装了全固态电致变色超级电容器原型器件, 当充电完成时器件的变色区域呈现墨绿色, 当放电完成时器件的变色区域呈现亮黄色。     

Water-processable polyaniline with covalently bonded single-walled carbon nanotubes: enhanced electrochromic properties and impedance analysis

Hybrid electrochromic materials were readily synthesized via copolymerization of aniline with p-phenylenediamine-functionalized single-walled carbon nanotubes (SWCNTs) in the presence of poly(styrene sulfonate) (PSS) dopant in an aqueous medium. Polyaniline (PANI)-grafted SWCNTs are formed, and they are uniformly dispersed in the PANI/PSS matrix. Impedance analysis shows that the charge-transfer resistances of the hybrids at all states are reduced drastically with increasing SWCNT loading. With 0.8 wt % SWCNTs, the charge-transfer resistances of the hybrid at +1.5 and -1.5 V are only about 20% and 12% of those of PANI/PSS, respectively, which is due to the greatly increased redox reactivity given by the enhanced electron transport in the hybrid and further doping function of the SWCNTs. The remarkable increase in redox reactivity leads to much enhanced electrochromic contrast from 0.34 for PANI to 0.47 for PANI-SWCNT-0.8%.     

改善有机片式固体钽电解电容器性能工艺研究

研究了在被膜过程中表面活性处理及掺杂对聚合物片式钽电容器容量、耐压、等效串联电阻(ESR)等特性的影响。研究结果表明表面活性处理后可以有效改善Ta2O5/PEDOT界面间的匹配,提高电容器容量引出效率;通过添加中间阻隔层(硅烷偶联剂)可以有效地阻挡杂质氧化性离子进入介质膜Ta2O5层,降低聚合物片式钽电容器的漏电流,提高耐压特性;实验结果表明在掺杂剂溶液的浓度为3%,补形成电压为赋能电压的70%时,能有效降低电容器ESR及漏电流。     

Ionic‐Liquid Doping Enables High Transconductance,Fast Response Time,and High Ion Sensitivity in Organic Electrochemical Transistors

Organic electrochemical transistors (OECTs) are highly attractive for applications ranging from circuit elements and neuromorphic devices to transducers for biological sensing, and the archetypal channel material is poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate), PEDOT:PSS. The operation of OECTs involves the doping and dedoping of a conjugated polymer due to ion intercalation under the application of a gate voltage. However, the challenge is the trade‐off in morphology for mixed conduction since good electronic charge transport requires a high degree of ordering among PEDOT chains, while efficient ion uptake and volumetric doping necessitates open and loose packing of the polymer chains. Ionic‐liquid‐doped PEDOT:PSS that overcomes this limitation is demonstrated. Ionic‐liquid‐doped OECTs show high transconductance, fast transient response, and high device stability over 3600 switching cycles. The OECTs are further capable of having good ion sensitivity and robust toward physical deformation. These findings pave the way for higher performance bioelectronics and flexible/wearable electronics.     

Vacuum vapour phase polymerised poly(3,4-ethyelendioxythiophene) thin films for use in large-scale electrochromic devices

Large-scale electrochromic devices were manufactured using vacuum vapour phase polymerised (VPP) poly(3,4-ethylenedioxythiophene) (PEDOT). Homogeneous 3,4-ethylenedioxythiophene (EDOT) and water vapour distribution within the large 115 L VPP chamber is paramount for the reproducible synthesis of high conductivity PEDOT thin films. Obtaining these conditions, however, was not trivial. The issue was resolved by synthesising PEDOT under vacuum, however, this altered the dynamics of the polymerisation process. As a result, surfactant addition, monomer and water vapour distribution, monomer and chamber temperature, and polymerisation times were all systematically investigated. Controlling these parameters has resulted in PEDOT with conductivity exceeding 1100 S · cm⁻¹, with a best of 1485 S · cm⁻¹, and electrochromic devices with an optical switch of Δ%Tx ≥ 50%. The resulting high conductivity and optical range are due to long undisrupted PEDOT polymer chains coupled with low levels of oligomers within the matrix.     

Novel synthesis of poly(3,4-ethylenedioxythiophene) nanotubes and hollow micro-spheres

A series of poly(3,4-ethylenedioxythiophene) (PEDOT) nanomaterials are prepared in aqueous solution without using any organic solvent, acid, surfactant and porous hard template. PEDOT can be tuned into different shapes, such as nano-tubes, spheres and vesicle-like particles by simply adjusting the experiment conditions. The different nanostructured products show similar electrochemical voltammogram behavior, though XRD and FTIR analysis indicate some different doping level and crystallity between them. The formation of different shaped polymer particles is supposed to be associated with the self assembly growth of the formed reactive EDOT species.     

Individually addressable crystalline conducting polymer nanowires in a microelectrode sensor array

An efficient, site-specific and scalable approach has been developed to produce high-quality and individually addressable conducting polymer nanowire electrode junctions (CPNEJs) in a parallel-oriented array. Polypyrrole and PEDOT conducting polymer nanowires (CPNWs) with uniform diameters (ca. 60-150?nm) were introduced into the desired electrode junctions in a precise manner by performing a three-step constant-current electrochemical process at a low current density and a low concentration of monomers. A low scan rate, cyclic voltammetric method was also employed and gave similar results. These CPNEJ arrays function as a miniaturized sensor for the parallel and real-time detection of gas and organic vapour. The electrochemical approaches utilized allow the conducting polymer chains to self-organize in the CPNWs to form novel polycrystalline structures, observed by high resolution TEM. The weak diffraction rings at 4.88?? and 4.60?? were observed for PEDOT and polypyrrole CPNWs, respectively.     

聚合物全固态电致变色器件的制备及性能

使用乙烯-乙烯醇共聚物/聚吡咯复合膜和聚醚基氨酯/LiClO4电解质制成全固态电致变色器件.当加上1.0～2.5V的直流电压时,器件颜色由黄色变成棕(蓝)色.详细讨论了器件的UV/VIS光谱变化、掺杂/不掺杂过程的响应时间以及电解质浓度对变色过程的影响.结果显示电致变色器件在800nm时,发生掺杂/不掺杂过程变化有短的响应时间和大的透过率差.     

A nanostructured electrochromic supercapacitor

We report the first successful application of an ordered bicontinuous double-gyroid vanadium pentoxide network in an electrochromic supercapacitor. The freestanding vanadia network was fabricated by electrodeposition into a voided block copolymer template that had self-assembled into the double-gyroid morphology. The highly ordered structure with 11.0 nm wide struts and a high specific surface to bulk volume ratio of 161.4 μm(-1) is ideal for fast and efficient lithium ion intercalation/extraction and faradaic surface reactions, which are essential for high energy and high power density electrochemical energy storage devices. Supercapacitors made from such gyroid-structured vanadia electrodes exhibit a high specific capacitance of 155 F g(-1) and show a strong electrochromic color change from green/gray to yellow, indicating the capacitor's charge condition. The nanostructuring approach and utilizing an electrode material that has intrinsic electrochemical color-change properties are concepts that can be readily extended to other electrochromic intercalation compounds.     

Enhancement-Mode PEDOT:PSS Organic Electrochemical Transistors Using Molecular De-Doping

Organic electrochemical transistors (OECTs) show great promise for flexible, low-cost, and low-voltage sensors for aqueous solutions. The majority of OECT devices are made using the polymer blend poly(ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), in which PEDOT is intrinsically doped due to inclusion of PSS. Because of this intrinsic doping, PEDOT:PSS OECTs generally operate in depletion mode, which results in a higher power consumption and limits stability. Here, a straightforward method to de-dope PEDOT:PSS using commercially available amine-based molecular de-dopants to achieve stable enhancement-mode OECTs is presented. The enhancement-mode OECTs show mobilities near that of pristine PEDOT:PSS (≈2 cm² V⁻¹ s⁻¹) with stable operation over 1000 on/off cycles. The electron and proton exchange among PEDOT, PSS, and the molecular de-dopants are characterized to reveal the underlying chemical mechanism of the threshold voltage shift to negative voltages. Finally, the effect of the de-doping on the microstructure of the spin-cast PEDOT:PSS films is investigated.