Extending the Utility of Conducting Polymers through Chemisorption of Nucleophiles

The investigation of poly­(3,4-ethylenedioxythiophene) (PEDOT) exposed to several example amines has shown that they bind to the conducting polymer through a nucleophilic attack on the positively charged carbon atoms. The PEDOT films were polymerized using the vacuum vapor phase polymerization (VPP) technique, and their electrical and optical properties subsequently modified by adsorbing aniline, ammonia or urea. Analysis of the surface chemistry shows that the reversibility of the binding depends on the nature of the amine, although a portion is chemisorbed to the PEDOT. This mechanism allows the polymer surface to be decorated with biomolecules or nanoparticles, as demonstrated by attachment of poly­(allylamine) coated silica nanoparticles to the PEDOT. This understanding provides the opportunity to control PEDOT properties, and opens the pathway to extend the utility of these electroactive, optoactive, and bioactive materials

Flexible Polymer-on-Polymer Architecture for Piezo/Pyroelectric Energy Harvesting

An all polymer piezo/pyroelectric device was fabricated using β phase poly­(vinylidene fluoride) (PVDF) as the active material and vapor phase polymerized (VPP) poly­(3,4-ethylenedioxythiphene) (PEDOT) as the flexible electrode overlay material. Inherent problems usually associated with coating polymeric electrodes onto the low surface energy PVDF were overcome by air plasma treating the film in conjunction with utilizing the VPP technique to simultaneously synthesize and in situ deposit the PEDOT electrode. Strain measurements up to the breaking-strain of PVDF (approximately 35%) indicated that the change in <i>R</i>/<i>R</i>_o was significantly smaller for the PEDOT based electrodes compared to the platinum electrode. Plasma treatment of the PVDF film increased the level of surface oxygenated carbon species that contributed to increased surface energy, as confirmed by confirmed by contact angle measurement. The enhanced adhesion between the two polymers layers contributed to a significant increase in the measured piezoelectric output voltage from 0.2 to 0.5 V for the same strain conditions. Pyroelectric voltage outputs were obtained by placing the film onto and off of a hotplate, for temperatures up to 50 °C above ambient. Finally, as a proof of concept, a simple energy harvesting device (plastic tube with slots for mounting multiple piezo/pyro films) was fabricated. The device was able to generate a usable level of peak output current (>3.5 μA) from human inhalation and exhalation “waste energy”

Cell attachment and proliferation on high conductivity PEDOT-glycol composites produced by vapour phase polymerisation

High conductivity poly(3,4-ethylene dioxythiophene) (PEDOT) was synthesised using vacuum vapour phase polymerization (VVPP). The process produces PEDOT composites which incorporate glycol within the polymer. To assess biocompatibility, a suite of analytical techniques were utilised in an effort to characterise the level of glycol present and its impact on cell attachment and proliferation. A small decrease in fibroblast cell attachment and proliferation was observed with increasing glycol content within the PEDOT composite. Keratinocyte cell attachment and proliferation by comparison showed an increase. As such, the results herein indicate that cell attachment and proliferation depends on the individual cell lines used and that the impact of glycol within the PEDOT composite is negligible. This positive outcome prompted investigation of this polymer as a platform for electro-stimulation work. Application of oxidising and reducing potentials to the PEDOT composite were utilised to examine the effect on biocompatibility. Significant effects were seen with altered protein presentation on the reduced surface, and lower mass adsorbed at the oxidised surface. Keratinocytes interacted significantly better on the reduced surface whereas fibroblasts displayed dependence on protein density, with significantly lower spreading on the oxidised surface. Understanding how proteins interact at electrically biased polymer surfaces and in turn affect cell behaviour, underpins the utilisation of such tunable surfaces in biomedical devices

Ultrathin polymer films for transparent electrode applications prepared by controlled nucleation

The vacuum vapor phase polymerization (VPP) technique is capable of producing conducting polymer films with conductivities up to 3400 S cm−1. However, the method is not able to produce robust nano-thin films as required for transparent conducting electrode (TCE) applications. We show that with the addition of aprotic solvents or chelating agents to the oxidant mixture, it is possible to control the polymerization rate, and nucleation, in the VPP process. This provides the opportunity of altering the grain size and depositing conducting polymer films with a thickness of 16 to 200 nm with resulting optical transmission within the range 50−98% that are robust enough to endure the post polymerization processing steps. The figure of merit (FoM), which is used to quantify a film’s suitability for TCE applications, results in values from 12 to 25. This result indicates that the nanofilms outperform most of the previously reported graphene films and approaches the accepted industry standard for TCE applications.

Using oxygen plasma treatment to improve the performance of electrodes for capacitive water deionization

An oxygen plasma treatment was employed to modify the surface of carbon electrodes used in capacitive deionization (CDI). X-ray photoelectron spectroscopy analysis of samples showed that oxygen plasma is mainly attaching oxygenated groups on the PTFE binder used in these electrodes. By functionalizing the binder it can increase the hydrophilicity of the electrode surface and increase the available specific surface area. 2.5 min of plasma treatment resulted in the largest improvement of CDI performance of electrodes. Thermodynamic study of CDI performance showed that the modified electrodes followed Langmuir and Freundlich isotherms resulting from the increased interaction between the enhanced electrodes and water. The kinetic study showed that the CDI process followed a pseudo-first order adsorption kinetics. The calculated adsorption rate constants suggested that plasma modification can accelerate ion adsorption of electrodes.

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.

Insights into the Oxidant/Polymer Interfacial Growth of Vapor Phase Polymerized PEDOT Thin Films

The vapor phase polymerization (VPP) technique is used to produce thinfilms of poly(3,4-ethylenedioxythiopene) (PEDOT) in which the Fe(III)Tosylateoxidant is altered. The oxidant is changed with the addition of an amphiphilicco-polymer having different molecular weights, namely 2800 Da. and 5800 Da.Resulting PEDOT films produce conductivities of ≈1500 and ≈3000 S cm−1respectively. Small angle X-ray diffraction (SA-XRD) indicates that the oxidantincorporating the larger molecular weight co-polymer possesses orderedstructure and that this in turn helps “template” the PEDOT during filmformation. The structure and composition of the bottom (i.e. initial filmformation) and top (i.e. final film formation) PEDOT surfaces are studiedusing surface sensitive analytical techniques; small angle X-ray diffraction(SA-XRD), ultraviolet photoelectron spectroscopy (UPS), 2D grazing incidenceX-ray diffraction (2D-GIXD), metastable induced electron spectroscopy (MIES)and neutral impact collision ion scattering spectroscopy (NICISS). The resultsindicate that the increase in conductivity using the larger molecular weightco-polymer additive is due to the film having larger lamella- and π-stackingregions in addition to doping levels which remain unchanged throughoutfilm formation. These conclusions are further supported by results obtainedon a model PEDOT:Tosylate system using density functional theory (DFT)calculations

Condensation and freezing of droplets on superhydrophobic surfaces

Superhydrophobic coatings are reported as promising candidates for anti-icing applications. Various studies have shown that as well as having ultra water repellency the surfaces have reduced ice adhesion and can delay water freezing. However, the structure or texture (roughness) of the superhydrophobic surface is subject to degradation during the thermocycling or wetting process. This degradation can impair the superhydrophobicity and the icephobicity of those coatings. In this review, a brief overview of the process of droplet freezing on superhydrophobic coatings is presented with respect to their potential in anti-icing applications. To support this discussion, new data is presented about the condensation of water onto physically decorated substrates, and the associated freezing process which impacts on the freezing of macroscopic droplets on the surface.

Polymeric material with metal-like conductivity for next generation organic electronic devices

The reduced pressure synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) with sheet-like morphology has been achieved with the introduction of an amphiphilic triblock copolymer into the oxidant thin film. Addition of the copolymer not only results in an oxidant thin film which remains liquid-like under reduced pressure but also induces structured growth during film formation. PEDOT films were polymerized using the vacuum vapor phase polymerization (VPP) technique, in which we show that maintaining a liquid-like state for the oxidant is essential. The resulting conductivity is equivalent to commercially available indium tin oxide (ITO) with concomitant optical transmission values. PEDOT films can be produced with a variety of thicknesses across a range of substrate materials from plastics to metals to ceramics, with sheet resistances down to 45 Omega/square (ca. 3400 S.cm(-1)), and transparency in the visible spectrum of >80% at 65 nm thickness. This compares favorably to ITO and its currently touted replacements