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Conducting polymers such as poly(3,4-ethylenedioxythiophene) (PEDOT) are widely researched for application in electronic devices. Researcher's look to exploit the ability of these polymers to conduct electrical charge. To induce conductivity, the polymers are doped with counterions; for PEDOT, this is typically done with poly(styrenesulfonate) or tosylate (Tos). The Tos anions inserted within the PEDOT nanostructure stabilize positive defects (holes) on the polymer's conjugated backbone, which, in turn, facilitates electrical conduction. In this study, we use X-ray photoelectron spectroscopy to investigate the Tos doping of PEDOT within the outermost region (< 15 nm) of electrochemically oxidized or reduced PEDOT:Tos nanoscale films. Computation of the predicted density of states from density functional theory studies is also conducted to aid in interpreting the ultraviolet photoelectron spectroscopy spectra. We observe that the doping of PEDOT:Tos is more complex than first thought, likely involving the nonionic triblock copolymer used during PEDOT's oxidative polymerization. This hypothesis is corroborated by time-of -flight secondary-ion mass spectrometry measurements on the outer 2 nm of the oxidized and reduced PEDOT:Tos. The observation of complex and heightened doping near the surface opens opportunities for the deliberate surface engineering of PEDOT:Tos nanofilms in polymer electronic applications such as electrochemical transistors and electrical connections. Refereed/Peer-reviewed

The properties of a thin film are, in part, governed by the nucleation or seeding of the material on a given substrate. Control over the seeding process is highly desirable, resulting in the ability to “dial up” desired film properties for the end application. In this study, we investigate the seeding process for thin films of Cr (thickness < 5 nm) sputtered onto polymeric substrates. These substrates are fabricated having Young’s moduli spanning from the rubbery to the glassy state. Compliant substrates in the rubbery state display nanowrinkled structures during the early stages of film deposition (seeding). The combined chemical and morphological analysis of these films suggests implantation of Cr clusters within the polymeric substrate—this implantation process is strongly influenced by substrate’s mechanical properties. Understanding the seeding process, the resultant nanowrinkles, and the evolution to a continuous ultrathin film, will have an impact on the way these systems are engineered for practical applications. Refereed/Peer-reviewed

Conducting polymers are promising candidates for wearable devices due to mechanical flexibility combined with electroactivity. While electrochemical measurements have been adopted as a central transduction method in many on-skin sensors, less studied is the stability of the active materials (in particular poly3,4-ethylenedioxythiophene, PEDOT) in such systems, particularly for “on-skin” applications. In this study, several different variants of doped PEDOT are fabricated and characterized in terms of their (electrical, physical, and chemical) stability in biological fluid. PEDOT doped with tosylate (TOS) or polystyrenesulfonate (PSS) are selected as prototypical forms of conducting polymers. These are compared with a new variant of PEDOT co-doped with both TOS and PSS. Artificial interstitial fluid (aISF) loaded with 1% wt/vol bovine serum albumin is adopted as the testing medium to demonstrate the stability in dermal applications (i.e., conducting polymer microneedles or coatings on microneedles). A range of techniques such as cyclic voltammetry and electrochemical impedance spectroscopy are used to qualify and quantify the stability of the doped conducting polymers. Furthermore, this study is extended by using human skin lysate in the aISF to demonstrate proof-of-concept for stable use of PEDOT in wearable “on-skin” electronics Refereed/Peer-reviewed

The biocompatibility of conducting polymer has seen remarkable advancement in numerous biomedical applications. The tuneable electrical property expressed by doping and de‐doping of the polymer has contributed to electrical controlled film in terms of volume and conductivity. Also, higher sensitivity specially for ionic molecules, bring forward new prospective in bio/sensing. Meanwhile, wearable devices for health care monitoring are becoming more prominent due to remote, real time and continuous monitoring. The flexible and stretchable property of organic electronic, in this paper represented by conducting polymer, as compared to rigid, conventional conductor unleashes high potential of conducting polymer as platform for wearable sensing device. In this review, properties of conducting polymers adopted in wearable devices focusing on on‐skin sensing is elaborated. The contribution of conducting polymers in various sensing targets, mainly categorized by chemical, tactile and electrophysiological are discussed, followed by types of the wearable sensors. Overall, our aim is to lay broader understanding of incorporation of the polymer within wearable sensing devices. Refereed/Peer-reviewed

Vapor deposition of tosylate-doped poly(3,4-ethylenedioxythiophene) (PEDOT) has been templated to create hollow nanosphere coatings on carbon paper electrodes. The electrochemistry of the PEDOT hollow nanosphere coatings were characterized in nonvolatile and nonflammable Li-based N-methyl-N-propyl pyrrolidinium bis(fluorosulfonyl)imide electrolytes. These electrodes exhibit high electrochemical activity for the given deposited mass owing to their heightened electrochemical active area. Furthermore, a multilayer of PEDOT hollow nanospheres as the cathode in a Li coin cell provides stability during repeated charge–discharge cycling against a Li–metal foil anode. With performance equivalent to the theoretical limit for PEDOT (140 mA h g–1), the Li|PEDOT cell has a significant specific energy of ∼340 W h/kg. These results give insights into the fabrication and use of nanostructured vapor-deposited conducting polymers for energy storage devices. usc Refereed/Peer-reviewed

The effect of thermal treatment on the structure and electrical/optical properties of vapor phase-polymerized poly(3,4-ethylenedioxythiophene):tosylate (PEDOT:Tos) and polypyrrole:tosylate (PPy:Tos) polymer films was investigated. Thermal treatment was applied postpolymerization but prior to washing the embedded oxidant layer out of the polymer film. Structural and chemical changes arising from the treatment were studied in the context of their conductive and electrochromic behavior. Spectroscopic analysis indicated a rise in the doping levels of both conductive polymers when exposed to thermal treatment. Additionally, an increase in the film thickness was recorded after the oxidant and other unbound species were removed from the polymer layer using an ethanol rinse. As such, a strong indication that polymerization continued even in the absence of (external) monomer vapor was present. This film thickness increase was most pronounced for PPy:Tos but also present in the PEDOT:Tos film. Heat-treated films exhibited enhanced cohesion, making them more robust and therefore increasing the viability for the material to be used in the optoelectronics area. This robustness, due to additional (cross-linking) oligomer growth, came at the expense of lower conductivity relative to their untreated counterparts. Refereed/Peer-reviewed

The one step fabrication of nanocomposite films of conducting polymers with 2D nanoparticles is investigated in this study. Specifically, the inclusion of nanomaterials (single layer graphene, single layer molybdenum disulfide) within PEDOT is achieved using the vapor phase polymerization (VPP) technique. This facile process allows for the formation of thin films of the order of less than 200 nm, which display a wide range of enhanced properties (mechanical, optical, and electrochemical). Herein, in a typical example with added graphene (

Polymers are lightweight, flexible, solution-processable materials that are promising for low-cost printed electronics as well as for mass-produced and large-area applications. Previous studies demonstrated that they can possess insulating, semiconducting or metallic properties; here we report that polymers can also be semi-metallic. Semi-metals, exemplified by bismuth, graphite and telluride alloys, have no energy bandgap and a very low density of states at the Fermi level. Furthermore, they typically have a higher Seebeck coefficient and lower thermal conductivities compared with metals, thus being suitable for thermoelectric applications.We measure the thermoelectric properties of various poly(3,4-ethylenedioxythiophene) samples, and observe a marked increase in the Seebeck coefficient when the electrical conductivity is enhanced through molecular organization. This initiates the transition from a Fermi glass to a semi-metal. The high Seebeck value, the metallic conductivity at room temperature and the absence of unpaired electron spins makes polymer semi-metals attractive for thermoelectrics and spintronics. Refereed/Peer-reviewed

Non-aqueous colloidal dispersions form the basis of many real-world applications, including electro-rheological fluids in automotive assemblies and inks in printing devices. The dispersion of particles within the non-aqueous liquid is typically stabilised by the use of dispersants, which adsorb to the particle/liquid interface and provide steric and/or electrical forces to prevent their aggregation. Importantly, the selection of the dispersant influences not only the inter-particle forces, but also their summation across many particles then defines the bulk properties of the suspension. Tailoring of these bulk properties is important in an industrial context, as each application will demand different bulk properties. In this study, the adsorption of three dispersants onto a polyester resin surface from a simple alkane is investigated. It is shown that the competition between the rates of adsorption from the bulk relative to that of the internal relocation of the functional groups of already adsorbed material defines the total adsorbed mass and structure of the film. Dispersants that have a slow rate of adsorption and a relatively fast rate of internal reorganisation produce soft visco-elastic layers with less total adsorbed mass. Conversely, dispersants with fast rates of adsorption and relatively low rates of reorganisation produce stiffer more elastic films and a greater total adsorbed mass. Refereed/Peer-reviewed