Roderick Shepherd

High-Performance Multifunctional Graphene Yarns: Toward Wearable All-Carbon Energy Storage Textiles

The successful commercialization of smart wearable garments is hindered by the lack of fully integrated carbon-based energy storage devices into smart wearables. Since electrodes are the active components that determine the performance of energy storage systems, it is important to rationally design and engineer hierarchical architectures atboth the nano- and macroscale that can enjoy all of the necessary requirements for a perfect electrode. Here we demonstrate a large-scale flexible fabrication of highly porous high-performance multifunctional graphene oxide (GO) and rGO fibers and yarns by taking advantage of the intrinsic soft self-assembly behavior of ultralarge graphene oxide liquid crystalline dispersions. The produced yarns, which are the only practical form of these architectures for real-life device applications, were found to be mechanically robust (Youngs modulus in excess of 29 GPa) and exhibited high native electrical conductivity (2508 ± 632 S m(-1)) and exceptionally high specific surface area (2605 m(2) g(-1) before reduction and 2210 m(2) g(-1) after reduction). Furthermore, the highly porous nature of these architectures enabled us to translate the superior electrochemical properties of individual graphene sheets into practical everyday use devices with complex geometrical architectures. The as-prepared final architectures exhibited an open network structure with a continuous ion transport network, resulting in unrivaled charge storage capacity (409 F g(-1) at 1 A g(-1)) and rate capability (56 F g(-1) at 100 A g(-1)) while maintaining their strong flexible nature.

Novel fused-LEDs devices as optical sensors for colorimetric analysis

The development of a novel, low power optical sensing platform based on light emitting diodes (LEDs) is described. The sensor is constructed from a pair of LEDs fused together at an angle where one LED functions as the light source and the other LED is reverse biased to function as a light detector. Sensor function is based on the level of light received by the detector diode, which varies with the reflectance of the interface between the device and its environment, or the chemochromic membrane that covers the device. A simple microprocessor circuit is used to measure the time taken for the photon-induced current to discharge the detector LED from an initial 5V (logic 1) to 1.7V (logic zero). This sensing device has been successfully used for colour and colour-based pH measurements and offers extremely high sensitivity, enabling detection down to the sub micro molar level of dyes.

Printing conducting polymers

Recent developments in both materials science and printing technologies have led to a rapid expansion in the field of printed conducting polymers. This review provides an overview of the most common printing methods currently in use and the material requirements of each. Examples of printed devices fabricated from a range of conducting polymers are given with an emphasis on the development of sensors.

Fabrication of Polyaniline-Based Gas Sensors Using Piezoelectric Inkjet and Screen Printing for the Detection of Hydrogen Sulfide

This work describes a fully printable polyaniline-copper (II) chloride sensor for the detection of hydrogen sulfide gas. The sensing device is composed of screen printed silver interdigitated electrode (IDE) on a flexible PET substrate with inkjet printed layers of polyaniline and copper (II) chloride. The sensor is employed as a chemiresistor with changes in measured current being correlated with concentration. On exposure to hydrogen sulfide, 2.5 ppmv (parts per million by volume) is clearly detectable with a linear relationship between measured current and concentration over the 10-100 ppmv region. The detection mechanism is discussed with respect to the hydrogen sulfide response, the choice of electrode materials in addition to UV-vis and surface enhanced Raman spectroscopy (SERS) characterization.

Inkjet printed LED based pH chemical sensor for gas sensing

Predictable behaviour is a critical factor when developing a sensor for potential deployment within a wireless sensor network (WSN). The work presented here details the fabrication and performance of an optical chemical sensor for gaseous acetic acid analysis, which was constructed using inkjet printed deposition of a colorimetric chemical sensor. The chemical sensor comprised a pH indicator dye (bromophenol blue), phase transfer salt tetrahexylammonium bromide and polymer ethyl cellulose dissolved in 1-butanol. A paired emitter-detector diode (PEDD) optical detector was employed to monitor responses of the colorimetric chemical sensor as it exhibits good sensitivity, low power consumption, is low cost, accurate and has excellent signal-to-noise ratios. The chemical sensor formulation was printed directly onto the surface of the emitter LED, and the resulting chemical sensors characterised with respect to their layer thickness, response time and recovery time. The fabrication reproducibility of inkjet printed chemical sensors in comparison to drop casted chemical sensors was investigated. Colorimetric chemical sensors produced by inkjet printing, exhibited an improved reproducibility for the detection of gaseous acetic acid with a relative standard deviation of 5.5% in comparison to 68.0% calculated for drop casted sensors (n=10). The stability of the chemical sensor was also investigated through both intra and inter-day studies.

Wholly printed polypyrrole nanoparticle-based biosensors on flexible substrate

Printing has been widely used in the sensor industry for its speed, low cost and production scalability. In this work we present a wholly-printed polypyrrole (PPy) based biosensor produced by inkjet printing bioinks composed of dispersions of PPy nanoparticles and enzymes onto screen-printed carbon electrodes. Two enzymes, horseradish peroxidase (HRP) or glucose oxidase (GoD) were incorporated into the PPy nanoparticle dispersions to impart biosensing functionality and selectivity into the conducting polymer ink. Further functionality was also introduced by deposition of a permselective ethyl cellulose (EC) membrane using inkjet printing. Cyclic voltammetry (CV) and chrono-amperometry were used to characterize the response of the PPy biosensors to H2O2 and glucose. Results demonstrated the possibility of PPy based biosensor fabrication using the rapid and low cost technique of inkjet printing. The detection range of H2O2 was found to be 10 μM-10 mM and for glucose was 1-5 mM.

Gemini surfactant doped polypyrrole nanodispersions: an inkjet printable formulation

We chemically synthesized inkjet printable polypyrrole (PPy) nanoformulations with reasonable conductivity for the first time in the presence of gemini surfactants 9BA-4-9BA (6,6′-(butane-1,4-diylbis(oxy)) bis(3-nonylbenzenesulfonic acid)) and 9B-4-9B (6,6′-(butane-1,4-diylbis(oxy)) bis(3-nonylbenzenesulfonic sodium)). Different oxidants and surfactants were investigated to optimize the surface tension, viscosity and conductivity of PPy dispersions to make it suitable for inkjet printing. Finally, a nanoformulation (maximum particle size < 200 nm) with low viscosity (9.4 mPa s), low surface tension (30.8 mN m−1) and reasonable cast conductivity (1.26 S cm−1) was obtained. This nanoformulation was printed successfully on different substrates and SEM images of a printed film on PVDF indicate that the size of the particles in the dispersion is 50 ± 5 nm. The conductivity of printed PPy/GA films on glass slides was as high as 0.7 S cm−1.

Conformational Changes in Sulfonated Polyaniline Caused By Metal Salts and OH

The fully sulfonated, water soluble polyaniline, poly(2-methoxyaniline-5-sulfonic acid), has been shown to be remarkably inert to alkaline dedoping, remaining in the conducting emeraldine salt form even in 2.0 M NaOH. Instead, its polyaniline chains undergo a conformational change from an extended coil to a compact coil structure. The same conformational change is caused, but more slowly, by the presence of added alkali and alkaline earth metal salts (1.0 M). These unprecedented rearrangements proceed via two steps, the speeds of which are sensitive to the nature of the metal ions and the associated anions. The processes are reversed by acid.

Efficiency of a compact elliptical planar ultra-wideband antenna based on conductive polymers

A planar antenna for ultra-wideband (UWB) applications covering the 3.1–10.6 GHz range has been designed as a test bed for efficiency measurements of antennas manufactured using polymer conductors. Two types of conductive polymers, PEDOT and PPy (polypyrrole), with very different thicknesses and conductivities have been selected as conductors for the radiating elements. A comparison between measured radiation patterns of the conductive polymers and a copper reference antenna allows to estimate the conductor losses of the two types of conductive polymers. For a 158 μm thick PPy polymer, an efficiency of almost 80% can be observed over the whole UWB spectrum. For a 7 μm thick PEDOT layer, an average efficiency of 26.6% demonstrates, considering the room for improvement, the potential of this type of versatile materials as flexible printable alternative to conductive metallic paints. The paper demonstrates that, even though the PEDOT conductivity is an order of magnitude larger than that of PPy, the thicker PPy layer leads to much higher efficiency over the whole UWB frequency range. This result highlights that high efficiency can be achieved not only through high conductivity, but also through a sufficiently thick layer of conductive polymers.

Galvanic coupling conducting polymers to biodegradable Mg initiates autonomously powered drug release

Electrical stimulation to affect localised and controlled release of therapeutic drugs is becoming an attractive option in the treatment of acute diseases or chronic illnesses. Currently the materials developed for this technique rely on power sources to operate, making their progression from the laboratory to the biomedical marketplace problematic. To help alleviate this issue, we have demonstrated autonomously powered controlled release of a drug by exploiting the galvanic couple between biodegradable Mg alloy and a conducting organic polymer. We also demonstrate the ability to control the rate of drug release by utilizing a range of biodegradable polymer coatings on the Mg alloy. Combination of the biodegradable Mg and conducting polymer provides a biocompatible platform for the autonomously controlled release of a drug at therapeutic levels.