Individually Addressable Suspended Conducting‐Polymer Wires in a Chemiresistive Gas Sensor

An effective method is described for producing poly(3,4‐ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) arched microwires, which are used as transducers in chemiresistive gas sensors. Three‐dimensional arched wires with diameters of 0.8, 1.2, 2.5, and 10 μm are individually fabricated by using a simple, inexpensive fountain‐pen lithography technique. The wires show superior stretchable behavior under omnidirectional strain of ca. 120%. A gas sensor assembled with the PEDOT:PSS arched wires exhibits linear responses to the concentrations of different vapor gases, such as ethanol, acetone, and methanol, at room temperature. The signal‐to‐noise ratio in the sensing response, which influences the detection limit, is enhanced by increasing the number of wires with a larger surface‐to‐volume ratio in parallel to increasing the signal level and diminishing the baseline noise in the wire transducers.

     

Enhancement of the Molecular Ordering via the Polymerization of 3,4‐Ethylenedioxythiophene‐Based Two‐Monomer‐Connected Precursor with 4,4‐Biphenyldisulfonic Acid

The polymerization of 3,4‐ethylenedioxythiophene (EDOT)‐based two‐monomer‐connected precursors in various solvent systems leads to improved crystallinity, compared to poly(3,4‐ethylenedioxythiophene) synthesized from traditional route. The P(EDOT:BPDSA:EDOT) is ordered by using 4,4‐biphenyldisulfonic acid (BPDSA) that is a connector and dopant linking EDOT monomers. The crystallinity, measured from X‐ray diffraction studies, is increased when using short chain or hydrophobic solvents. The crystallinity of P(EDOT:BPDSA:EDOT) significantly increases up to 45.0% compared to polymer with other sulfonic acids, bifunctional 1,2‐ethanesulfonic acid, and monofunctional methanesulfonic acid (MSA). The crystal structure is also confirmed from high‐voltage electron microscope. From these studies, it is confirmed that P(EDOT:BPDSA:EDOT) has an orthorhombic structure, which has the unit cell lattice parameters of a = 1.44 nm, b = 0.98 nm, and c = 1.18 nm from fast Fourier transform pattern images. The electrical conductivity is increased about four times with BPDSA (0.21 S cm^?1) when compared using MSA (0.06 S cm^?1).     

Electrochromic Response of Nanostructured Poly(3,4‐ethylenedioxythiophene) Films Grown in an Aqueous Micellar Solution

Poly(3,4‐ethylenedioxythiophene) (PEDOT) films have been electropolymerized from an aqueous micellar solution encompassing the monomer (EDOT) and the moieties sodium dodecyl sulfate (SDS) and lithium triflate. The presence of these anionic dopants in the polymer matrix and a doping level of 0.26 have been confirmed by X‐ray photoemission and electron paramagnetic resonance (EPR) spectroscopy. The hydrophobic micellar core encompassing the monomer orchestrates the growth of a uniform homogeneous polymer deposit as electron microscopy and atomic force microscopy studies reveal the film to be composed of a continuous interlinked network of quasi‐spherical grains (50–150 nm in dimensions) and pores alongwith a low surface roughness. The film exhibits a large coloration efficiency of 153 cm² · C^?1 and a transmission modulation of 62% (λ = 632.8 nm), which are manifestations of the open ion‐permeable morphology. The Q_{(inserted/extracted)} ratio ranges between 1.2 and 1.4 when cycled back and forth between the clear and blue states 2 500 times, thereby affirming the suitability of these films for practical electrochromic smart windows.

     

An Assessment of the Effect of Synthetic and Doping Conditions on the Processability and Conductivity of Poly(3,4‐ethylenedioxythiophene)/Poly(styrene sulfonic acid)

Poly(3,4‐ethylenedioxythiophene)/poly(styrene sulfonic acid) (PEDOT/PSS) dispersions are synthesized via conventional oxidative polymerization under various synthetic (reaction times and formulations) and doping conditions (in situ and postpolymerization) with the introduction of dialysis as an additional purification step. Conductivities of films produced from these synthesized dispersions are one to three orders of magnitude higher than the equivalent commercial PEDOT/PSS reference film. In situ doped PEDOT/PSS dispersions give films that are more conductive than those doped postpolymerization. Optimum conductivity of 5.2 ± 0.7 S cm^?1 is obtained from PEDOT/PSS dispersions (1:2.5 EDOT:PSS mass ratio) synthesized for 12 h with doping efficiency of 73%. Under these synthetic conditions, the film most likely has the optimal microstructure, i.e., optimal PEDOT chain length and ideal distribution and balance of PEDOT/PSS segments and free PSS chains, favoring charge transport and processability. Capillary electrophoresis is presented here as a novel method for measuring free and doped PSS in PEDOT/PSS dispersions.

     

Electrochemical Polymerization of Bis(3,4‐ethylenedioxythiophene)‐Substituted 1,4‐Diketo‐3,6‐diphenyl‐pyrrolo[3,4‐c]pyrrole (DPP) Derivative

Synthesis and electropolymerization of the new bisthienyl‐substituted diketopyrrolopyrrole monomer 1,4‐diketo‐2,5‐di‐hexyl‐3,6‐bis{[2‐(3',4'‐ethylenedi‐oxy)thienyl]phenyl}pyrrolo[3,4‐c]pyrrole (EDOT‐DPP‐EDOT) is reported. EDOT‐DPP‐EDOT exhibits a low oxidation potential of 0.67 V versus ferrocene and can be electropolymerized to form a stable, well adherent polymer thin film at the ITO anode. The polymer film is insoluble in organic solvents, non‐fluorescent, but exhibits reversible electrochromic properties with color changes from deep blue in the neutral state via transparent gray to purple red in the oxidized state. The reversibility in air is excellent.

     

Enhancement of Strain‐Sensing Performance through Gas Phase Incorporation of Siloxane into Thermoplastic Polyurethane‐Conducting Polymer Composite

In this study, thermoplastic polyurethane (TPU)‐conducting polymer (CP)–SiO₂ hybrid strain sensors are fabricated via the simultaneous co‐vaporization of a CP monomer with tetraethyl orthosilicate (TEOS). Poly(3,4‐ethylenedioxythiophene) (PEDOT) and polypyrrole (PPy) hybrids prepared using the oxidant, iron (III) p‐toluenesulfonate hexahydrate (FTS) with TPU as the substrate are explored along with the effect of hybridization on their sensing performance and mechanical properties. The SiO₂ is mostly formed on the surface and the CP is successfully polymerized within the TPU matrix. The sensor can be stretched further by up to 290% more than the pristine counterpart. Moreover, stretch‐release cycles show an increase in the relative resistance of the sensor by up to 89%, thereby improving its sensitivity. The sensors can detect motion at various strain levels, different speeds, and continuous deformation at different strains. The sensor’s reliability is tested by up to 1000 cycles at 10% strain, as well as other kinds of distortion such as bending and twisting. The created organic‐inorganic hybrid sensor exhibits a synergistic enhancement of both its mechanical properties and electromechanical performance. Furthermore, the processability of the elastomer and the versatility of the incorporated siloxane component have allowed the homogeneous distribution of the active elements (PEDOT, PPy).     

Increased Electrical Conductivity in Poly(3,4‐ethylenedioxythiophene) upon Cross‐Linking

Cross‐linked poly(3,4‐ethylenedioxythiophene) (PEDOT) films were synthesized by the oxidative polymerization of 3,4‐ethylenedioxythiophene in the presence of five different conjugated and non‐conjugated cross‐linkers. The concentration and structure of the cross‐linker was systematically varied to explore the influence on the electrical conductivity. Optimized compositions displayed an electrical conductivity of up to ≈800 S · cm^?1; this corresponds to a conductivity increase of up to 36% compared to linear PEDOT prepared under identical conditions. An increase in the conductivity was only observed for the conjugated cross‐linkers that were incorporated in low concentrations, typically at a level of less than 2 mol‐%. Attempts to incorporate higher concentrations of cross‐linker led to phase separation and crystallization of the cross‐linker and afforded materials in which a significant reduction of the electrical conductivity was observed. The optical properties of the polymer were only marginally affected upon cross‐linking, even at high cross‐linker concentrations.

     

Novel Low Bandgap EDOT‐Naphthalene Bisimides Conjugated Polymers: Synthesis,Redox, and Optical Properties

Low band‐gap conjugated polymers based on naphthalene bisimide (NBI) and 3,4‐ethylenedioxythiophene (EDOT) were synthesized by Stille cross‐coupling reaction. The alternating conjugated poly(EDOT‐NBI) ( P1 ) and random poly(EDOT‐NBI) ( P2 ) are both solution‐processable due to the existence of bulky 2,6‐diisopropylphenyl substituent. Their optical and electrochemical properties were characterized. P1 and P2 films show optical band gaps of 1.75 and 1.38 eV estimated from UV‐Vis absorption spectra. Cyclic voltammograms of both polymers display reversible reduction peaks with onset reduction potentials at ?0.55 V for P1 and ?0.61 V for P2 , which correspond to the electron affinity (EA) values (LUMO energy level) of 3.85 and 3.79 eV, respectively. The ionization potential (IP, HOMO level) values of 5.60 eV for P1 and 5.17 eV for P2 were also calculated by combining solid‐state optical and electrochemical data. A double heterojunction device was fabricated. It exhibits an open circuit voltage of 0.30 V and average power conversion efficiency of 0.15%.