Freestanding Functional Structures by Aerosol-Jet Printing for Stretchable Electronics and Sensing Applications

The requirements for modern electronic devices, particularly those intended for wearable or human health monitoring applications, have rapidly evolved to being both flexible and stretchable. Hence devices, as well as interconnects, need to be capable of retaining functionality even when being mechanically deformed. Most approaches towards achieving this rely on printing or transferring structures onto elastomeric substrates that can withstand stretching. However, the processing involved can often be cumbersome, and the structures themselves tend to suffer from poor fatigue and/or are limited by the mechanical properties of the underlying substrate. Here, we introduce an aerosol-jet printing technique by which fully freestanding functional structures can be built up layer by layer, which are stable and robust upon repeated stretching. The process involves printing a combination of layers of different materials with the desired functionality, onto a substrate coated with a sacrifical film that is subsequently dissolved to release the printed structure. Using this method, we demonstrate freestanding conductive wires can be used as stretchable interconnects/electrodes, and that also function as strain-sensors. We also show that a freestanding capacitive structure functions as a robust, stretchable humidity sensor, paving the way for the development of other multi-layer, multifunctional stretchable devices and sensors

Enhanced piezoelectricity and electromechanical efficiency in semiconducting GaN due to nanoscale porosity

Electrical polarization phenomena in GaN are important as they have significant impact on the operation of modern day energy efficient lighting and are fundamental to many GaN-based high power and high frequency electronics. Controlling polarization is beneficial for the optimization of these applications. GaN is also piezoelectric, and therefore mechanical stress and strain are possible handles to control its polarization. Nonetheless, polar semiconductors in general, and GaN in particular, are weak piezoelectric materials when compared to ceramics, and are therefore not considered for characteristic electromechanical applications such as sensing, actuation and mechanical energy harvesting. Here, we examine the effect of nanoscale porosity on the piezoelectricity of initially conductive GaN. We find that for 40% porosity, the previously conductive GaN layer becomes depleted, and exhibits enhanced piezoelectricity as measured using piezoresponse force microscopy, as well as by using a mechanical energy harvesting setup. The effective piezoelectric charge coefficient of the porous GaN, d33,eff, is found to be about 8 pm/V which is 2 3 times larger than bulk GaN. A macroscale device comprising a porous GaN layer delivered 100 nW/cm2 across a resistive load under a 150 kPa mechanical excitation. We performed finite element simulations to analyze the evolution of the piezoelectric properties with porosity. The simulations suggest that increased mechanical compliance due to porosity gives rise to the observed enhanced piezoelectricity in GaN. Furthermore, the simulations show that for stress-based excitations, the porous GaN electromechanical figure of merit is increased by an order of magnitude and becomes comparable to that of barium titanate piezoceramics. In addition, considering the central role played by GaN in modern electronics and optoelectronics, our study validates a very promising research direction when considering stress-based electromechanical applications which combine GaN’s semiconducting and piezoelectric properties

Tailoring the triboelectric output of poly-L-lactic acid nanotubes through control of polymer crystallinity

Funder: Emmanuel College (University of Cambridge); doi: http://dx.doi.org/10.13039/501100000609Abstract Triboelectric devices capable of harvesting ambient mechanical energy have attracted attention in recent years for powering biomedical devices. Typically, triboelectric energy harvesters rely on contact-generated charges between pairs of materials situated at opposite ends of the triboelectric series. However, very few biocompatible polymeric materials exist at the ‘tribopositive’ end of the triboelectric series. In order to further explore the use of triboelectric energy harvesting devices within the body, it is necessary to develop more biocompatible tribopositive materials and look into ways to improve their triboelectric performance in order to enhance the harvested power output of these devices. Poly-L-lactic acid (PLLA) is a tribopositive biocompatible polymer, frequently used in biomedical applications. Here, we present a way to improve the triboelectric output of nanostructured PLLA through fine control of its crystallinity via a customised template-assisted nanotube (NT) fabrication process. We find that PLLA NTs with higher values of crystallinity (∼41%) give rise to a threefold enhancement of the maximum triboelectric power output as compared to NTs of the same material and geometry but with lower crystallinity (∼13%). Our results thus pave the way for the production of a viable polymeric and biocompatible tribopositive material with improved power generation, for possible use in implantable triboelectric nanogenerators.</jats:p

COVID-19: time to rethink palliative care strategy in resource-poor settings

'No abstract

Enhanced Piezoelectricity of Electrospun Polyvinylidene Fluoride Fibers for Energy Harvesting

Piezoelectric polymers are promising energy materials for wearable and implantable applications for replacing bulky batteries in small and flexible electronics. Therefore, many research studies are focused on understanding the behavior of polymers at a molecular level and designing new polymer-based generators using polyvinylidene fluoride (PVDF). In this work, we investigated the influence of voltage polarity and ambient relative humidity in electrospinning of PVDF for energy-harvesting applications. A multitechnique approach combining microscopy and spectroscopy was used to study the content of the β-phase and piezoelectric properties of PVDF fibers. We shed new light on β-phase crystallization in electrospun PVDF and showed the enhanced piezoelectric response of the PVDF fiber-based generator produced with the negative voltage polarity at a relative humidity of 60%. Above all, we proved that not only crystallinity but also surface chemistry is crucial for improving piezoelectric performance in PVDF fibers. Controlling relative humidity and voltage polarity increased the d33 piezoelectric coefficient for PVDF fibers by more than three times and allowed us to generate a power density of 0.6 μW·cm-2 from PVDF membranes. This study showed that the electrospinning technique can be used as a single-step process for obtaining a vast spectrum of PVDF fibers exhibiting different physicochemical properties with β-phase crystallinity reaching up to 74%. The humidity and voltage polarity are critical factors in respect of chemistry of the material on piezoelectricity of PVDF fibers, which establishes a novel route to engineer materials for energy-harvesting and sensing applications

Registration of ‘Serenut 5R’ Groundnut

‘Serenut 5R’ (Reg. No. CV-129, PI 676092) is a new high-yielding, spanish-type groundnut (Arachis hypogaea L. subsp. fastigiata var. vulgaris) with two seeds per pod. Serenut 5R was released in 2010 by the National Semi-Arid Resources Research Institute, Soroti, Uganda. It was a selection from the ICRISAT advanced line ICGV-SM 93535. Serenut 5R originated from a cross made between ICGM 522 and ‘RG 1’. ICGV-SM 93535 was developed by using repeated bulk selections for groundnut rosette disease resistance, using the infector row technique at the ICRISAT-Malawi research station. Performance tests in replicated trials were performed in Uganda in 2008 and 2009. Trials were performed in two seasons each year and averaged over 10 rainfed locations in Uganda. Serenut 5R matures in 100 to 110 d, similar to the widely grown control cultivar Serenut 3R. Serenut 5R resulted in significantly higher pod yields (16%) than Serenut 3R, and the shellout percentage for Serenut 5R was 4.8% higher than Serenut 3R. Seed testa is red, and the seeds are slightly larger than those of Serenut 3R. The sound mature kernel count for Serenut 5R was 38.7 g 100−1 compared with 32.38 g 100−1 for Serenut 3R, an increase of 19.51%. The dormancy period for Serenut 5R was significantly less than Serenut 3R

Registration of ICG 12991 peanut germplasm line

ICG 12991 is a short duration (90–110 d to maturation), drought-tolerant, spanish-type peanut (Arachis hypogaea L. subsp. fastigiata Waldron var. vulgaris Harz.) germplasm line (Reg. no. GP-122, PI 639691) with a high level of field resistance to groundnut rosette disease (Naidu et al., 1999a; Subrahmanyam et al., 2000). Groundnut rosette disease results from a synergism of three agents: Groundnut rosette assistor virus (GRAV, a luteovirus), Groundnut rosette virus (GRV, an umbravirus), and a satellite RNA (sat RNA) of GRV. ICG 12991 was originally collected from a farmer’s field in south India in 1988. In 1994, ICRISAT introduced ICG 12991 into Malawi for evaluation during a germplasm screening program for resistance to groundnut rosette disease and early leaf spot disease (caused by Cercospora arachidicola S. Hori). Subsequently, ICG 12991 was released in Malawi as ‘Baka’ in 2001 and in Uganda as ‘Serenut 4T’ in 2002, following extensive testing and distribution by the national programs of each country. Resistance to groundnut rosette disease in ICG 12991 is due to aphid resistance, not due to resistance to the virus complex (Naidu et al., 1999b)

Registration of groundnut cultivar ICGV-SM 90704 with resistance to groundnut rosette

ICGV-SM 90704 is a high-yielding medium-duration groundnut germplasm developed at ICRISAT, Lilongwe, Malawi. It was derived from a cross between varieties RG1 and Mani Pintar, made in 1983. It was released in Uganda in 1999 as Serenut 2 and in Malawi in 2000 as ICGV-SM 90704. ICGV-Sm 90704 is resistant to groundnut rosette virus (GRV) but susceptible to aphid vector (Aphis craccivora) for GRV transmission. The yield performance, plant and seed characters of ICGV-SM 90704 are briefly described

Recent advances and perspectives on starch nanocomposites for packaging applications

Starch nanocomposites are popular and abundant materials in packaging sectors. The aim of this work is to review some of the most popular starch nanocomposite systems that have been used nowadays. Due to a wide range of applicable reinforcements, nanocomposite systems are investigated based on nanofiller type such as nanoclays, polysaccharides and carbonaceous nanofillers. Furthermore, the structures of starch and material preparation methods for their nanocomposites are also mentioned in this review. It is clearly presented that mechanical, thermal and barrier properties of plasticised starch can be improved with well-dispersed nanofillers in starch nanocomposites