Kahagala Gamage Upul Wijayantha

The coffee ring effect regularly occurs during the evaporation of colloidal droplets and is often undesirable. Here we show that adding a specific concentration of a surfactant can mitigate this effect. We have conducted experiments on aqueous suspensions of carbon nanotubes that were prepared with cationic surfactant dodecyltrimethylammonium bromide added at 0.2, 0.5, 1, 2, 5, and 10 times the critical micelle concentration. Colloidal droplets were deposited on candidate substrates for printed electronics with varying wetting characteristics: glass, polyethylene terephthalate, fluoroethylene propylene copolymer, and polydimethylsiloxane. Following drying, four pattern types were observed in the final deposits: dot-like, uniform, coffee ring deposits, and combined patterns (coffee ring with a dot-like central deposit). Evaporation occurred predominantly in constant contact radius mode for most pattern types, except for some cases that led to uniform deposits in which early stage receding of the contact line occurred. Image analysis and profilometry yielded deposit thicknesses, allowing us to identify a coffee ring subfeature in all uniform deposits and to infer the percentage coverage in all cases. Importantly, a critical surfactant concentration was identified for the generation of highly uniform deposits across all substrates. This concentration resulted in visually uniform deposits consisting of a coffee ring subfeature with a densely packed center, generated from two distinct evaporative phases.

Triboelectric nanogenerators (TENGs) are foreseen as a leading candidate to harvest mechanical energy from ambient sources such as human body movements. However, wearable TENGs, which are used for this purpose, require adequate wearability for long durations, in addition to sufficient electrical outputs. So far, it has been difficult to achieve this through the predominantly plastic-based wearable TENGs constructed using conventional nanogenerator fabrication methods. This Article evaluates the use of textile materials and scalable fabrication techniques to develop TENGs targeting balanced electrical and wearable properties. The fabrication process is conducted using yarn-coating, dip-coating, and screen-printing techniques, which are common textile manufacturing methods, and converted into fabrics using flat-bed knitting, resulting in TENGs with improved wearable and electrical performances. The electrical properties (open circuit voltage (V_oc), short circuit current (I_sc), and short circuit charge (Q_sc)) and wearable properties (air permeability, stretch and recovery, and moisture management) of these structures are evaluated, during which the yarn-coated TENG resulted in maximum electrical outputs recording V_oc ≈ 35 V, I_sc ≈ 60 nA, and Q_sc ≈ 12 nC, under mild excitations. In terms of wearability, the yarn-coated TENG again performed exceptionally during the majority of tests providing the best moisture management, air permeability (101 cm³/cm²/s), and stretch (∼75%), thus proving its suitability for wearable TENG applications.

Electronic waste produced by plastic, toxic, and semiconducting components of existing electronic devices is dramatically increasing environmental pollution. To overcome these issues, the use of eco-friendly materials for designing such devices is attaining much attention. This current work presents a recycled material-based triboelectric nanogenerator (TENG) made of plastic waste and carbon-coated paper wipes ([email protected]), in which the PWs are also collected from a waste bin. The resultant [email protected] TENG is then used for powering low-power electronic devices and, later, to generate a Morse code from a wearable for autonomous communication. In this application, the end users decode the Morse code from a customized LabVIEW program and read the transmitted signal. With further redesigning, a 9-segment keyboard is developed using nine-TENGs, connected to an Arduino controller to display the 9-segment actuation on a computer screen. Based on the above analysis, our [email protected] device is expected to have an impact on future self-powered sensors and internet of things systems.

In this research, fully metal oxide, capacitive humidity sensors for printed electronic applications have been designed and fabricated through the development of conductive indium tin oxide and dielectric aluminum oxide inks for the screen-printing process. Sensors were printed in a parallel plate configuration in 4 and 9 cm² conductive plate areas. Typically, commercially available discrete humidity sensors have a sensitivity in the range of 0.2–0.5 pF/RH%, whereas the printed humidity sensors presented in this paper have sensitivities of 0.85–7.76 pF/RH% depending on the sensor size, allowing for customizable properties. Response times were measured using a weighted average and found to be 21.4 s on average and recovery times were 4.8 s on average. The sensing performance was highly linear (R² > 0.97) for sensors of all sizes across the measured humidity range of 5–95%. Impedance spectroscopy was used to determine the sensing mechanism, and the mechanism was simulated and matched with experimental data. The sensing mechanism analysis shows that the sensing is primarily dictated by alumina at a lower relative humidity. The ITO contributes through increasing the ionic conductivity at a higher relative humidity, contributing to the high linearity of the sensor.

Manufactured resistors in conventional electronics are classified into tolerance groups ranging from <1% for high stability film types (E192) to 20% (E6) which are often carbon-based and utilised in less critical resistance value contexts such as current limiting or pull-up/down applications [IEC 60063:2015, Preferred number series for resistors and capacitors. One of the major identified challenges in the printed electronics industry currently is the ability to match this manufacturing capability for printed resistors in terms of initial tolerance, stability over time and power capabilities. In this work, a variety of screen-printed carbon resistors were designed and produced. The effects of utilising additional screen-printed ZnO and Ag layers as thermal variance management for the carbon resistors are investigated with the aim of improving the resistors power rating and stability. The introduction of ZnO or ZnO/Ag layers to carbon resistors saw notable improvements in the peak power capability, stability when sustaining 500 mW power dissipation, and stability in varying environmental conditions. Utilizing ZnO and Ag layers also notably improved the initial tolerance groupings when compared to basic uncoated carbon resistors.

Electrokinetic transport of a charged dye within a free liquid film stabilised by a cationic surfactant, trimethyl(tetradecyl)ammonium bromide (TTAB), subjected to an external electric field was investigated. Confocal laser scanning microscopy was used to visualise fluorescein isocyanate (FICT) separation within the stabilised liquid film. Numerical simulations were performed using Finite Element Method to model the dynamics of charged dye separation fronts observed in the experiments. Due to the electrochemical reactions at the electrodes, significant spatial and temporal pH changes were observed within the liquid film. These local pH changes could affect the local zeta potential at the gas-liquid and solid-liquid film boundaries; hence the flow field was found to be highly dynamic and complex. The charged dye (FICT) used in the experiments is pH sensitive, therefore electrophoresis of the dye also depended on the local pH. The pH and the electroosmotic flow field predicted from the numerical simulations were useful for understanding charged dye separation near both the anode and the cathode.

The mass commercialization of electronic textiles is currently hindered due to the lack of reliable manufacturing technologies of energy storing textiles. To incorporate energy storage as a part of a garment, it must be manufactured in a systematic manner, allowing the integration of multiple components of electronic textiles simultaneously. Aiming towards process automation, carbon-based screen-printing inks were formulated for textile supercapacitor applications, focusing on the effect of carbon additives in the electrochemical performance. Devices were assembled, and their electrochemical performance was assessed. The maximum areal power density obtained was 12 mW cm⁻² with an areal energy density of 1.08 × 10⁻³ mWh cm⁻².

A rapid 3 minute one-pot microwave synthesis of Pd–TiO₂ showing improved activity for photocatalytic nitrate reduction into ammonia.