Surface Potential Driven Water Harvesting from Fog.

Access to clean water is a global challenge, and fog collectors are a promising solution. Polycarbonate (PC) fibers have been used in fog collectors but with limited efficiency. In this study, we show that controlling voltage polarity and humidity during the electrospinning of PC fibers improves their surface properties for water collection capability. We experimentally measured the effect of both the surface morphology and the chemistry of PC fiber on their surface potential and mechanical properties in relation to the water collection efficiency from fog. PC fibers produced at high humidity and with negative voltage polarity show a superior water collection rate combined with the highest tensile strength. We proved that electric potential on surface and morphology are crucial, as often designed by nature, for enhancing the water collection capabilities via the single-step production of fibers without any postprocessing needs

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

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

Electrospun polymer fibers for triboelectric energy harvesting applications in smart textiles

Wearable biosensors embedded into smart textiles have the potential to revolutionise healthcare by enabling the measurement of vital signs in real-time. However, the deployment of these devices is hindered by their power requirements. Current batteries are too bulky and rigid, and require frequent charging. A promising solution to this issue involves energy harvesting devices capable of transforming surrounding waste energy into useful electricity, potentially reducing the battery size and frequency of charging. Amongst energy harvesters, triboelectric generators are excellent candidates for smart textile applications due to their potential to convert mechanical energy arising from body movements into electrical energy. Typically, triboelectric energy harvesters rely on contact-generated charges between pairs of materials situated at opposite ends of the triboelectric series, which is an empirical scale that ranks materials according to their charge donating/accepting tendencies. Such devices can be manufactured into yarns by coating a conductive core with a triboelectric material. However, current triboelectric yarns lack the power output, durability and washing resistance required for textile-based applications. This work addresses these issues by developing nanostructured functional polymer coatings, namely Nylon-11, polymethyl methacrylate (PMMA) and polyvinylidene difluoride (PVDF), using electrospinning, which is a widely used, scalable fiber-production method. These materials are selected because they respectively occupy the top, middle and bottom of the triboelectric series and are thus representative of a wide spectrum of triboelectric materials. Multiple electrospinning processing parameters including voltage polarity, humidity and polymer concentration are optimised to enhance energy harvesting performance and durability of triboelectric generators. The effects of processing on the resulting polymer crystal structure and surface properties, and subsequently triboelectric performance, are investigated in detail using a combination of characterisation techniques, including scanning probe microscopy, X-ray diffraction and infrared spectroscopy. Optimised Nylon-11 and PVDF coatings are subsequently used to develop tribopositive and tribonegative yarns. The triboelectric yarns are fabricated using a customised electrospinning process in which the polymer is directly spun onto a conductive carbon nanotube yarn, which serves as the conducting electrode. This method creates a uniform and stable core-shell structure with excellent adhesion between the polymer coating and the conducting core. The two triboelectric yarns exhibit remarkable triboelectric energy harvesting during fatigue testing with an average 35\% power output improvement after 200,000 fatigue cycles. Furthermore, the triboelectric yarns demonstrate high abrasion and water resistance by retaining their functionality following hundreds of rubbing and 10 washing cycles. Finally, the Nylon-11 and PVDF yarns are woven together creating a proof-of-concept triboelectric textile. The textile showed high peak power density output compared to previously reported devices (237 mW/m$^{2}$ across an impedance matched load resistance, in response to an applied mechanical force of 2 N and 2 Hz). Furthermore, the motion-sensing capabilities of the textile were demonstrated by building a textile-based touchpad and force sensor. In summary, the unique yarn fabrication process and the resulting high-performance triboelectric yarns are promising platform technologies that can accelerate the development of smart textiles beyond energy harvesting

Research data supporting 'Tailoring the triboelectric output of poly-L-lactic acid nanotubes through control of polymer crystallinity'

Experimental data from investigation into the effect of crystallinity on the triboelectric output of PLLA nanotubes. Results from XRD, KPFM, SEM and electrical output are included

Research data supporting Triboelectric Yarns with Electrospun Functional Polymer Coatings for Highly Durable and Washable Smart Textile Applications

Dataset for Triboelectric Yarns with Electrospun Functional Polymer Coatings for Highly Durable and Washable Smart Textile Applications. The dataset is divided into folders each containing the raw data of each figure in the publication. The data format is text, csv and excel for graphs. The images are in jpg format. The atomic force microscopy data can be accessed using Nanoscope Analysis software (Bruker) or with Python using the pySPM package

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

Triboelectric Yarns with Electrospun Functional Polymer Coatings for Highly Durable and Washable Smart Textile Applications.

Triboelectric generators are excellent candidates for smart textiles applications due to their ability to convert mechanical energy into electrical energy. Such devices can be manufactured into yarns by coating a conductive core with a triboelectric material, but current triboelectric yarns lack the durability and washing resistance required for textile-based applications. In this work, we develop a unique triboelectric yarn comprising a conducting carbon nanotube (CNT) yarn electrode coated with poly(vinylidene fluoride) (PVDF) fibers deposited by a customized electrospinning process. We show that the electrospun PVDF fibers adhere extremely well to the CNT core, producing a uniform and stable triboelectric coating. The PVDF-CNT coaxial yarn exhibits remarkable triboelectric energy harvesting during fatigue testing with a 33% power output improvement and a peak power density of 20.7 μW cm-2 after 200 000 fatigue cycles. This is potentially due to an increase in the active surface area of the PVDF fiber coating upon repeated contact. Furthermore, our triboelectric yarn meets standard textile industry benchmarks for both abrasion and washing by retaining functionality over 1200 rubbing cycles and 10 washing cycles. We demonstrate the energy harvesting and motion sensing capabilities of our triboelectric yarn in prototype textile-based applications, thereby highlighting its applicability to smart textiles

Research data supporting "Freestanding Functional Structures by Aerosol-Jet Printing for Stretchable Electronics and Sensing Applications"

This data was collected from the labs of Device Materials Group, Department of Materials Science and Metallurgy, University of Cambridge, between Dec 2016 to Jan 2019. The data contains resistance values measured from the printed device at various conditions such as stretching, fatigue test or different composite. The data also contains profile value of the thickness of the printed device. There are also current and voltage measurements on the LED during lighten up with the printed wire, as well as various capacitance data when the devices were applied as humidity sensor.European Commission (639526) European Commission Horizon 2020 (H2020) Marie Sklodowska-Curie actions (702868) EPSRC (EP/P007767/1

Surface Potential Driven Water Harvesting from Fog.

Access to clean water is a global challenge, and fog collectors are a promising solution. Polycarbonate (PC) fibers have been used in fog collectors but with limited efficiency. In this study, we show that controlling voltage polarity and humidity during the electrospinning of PC fibers improves their surface properties for water collection capability. We experimentally measured the effect of both the surface morphology and the chemistry of PC fiber on their surface potential and mechanical properties in relation to the water collection efficiency from fog. PC fibers produced at high humidity and with negative voltage polarity show a superior water collection rate combined with the highest tensile strength. We proved that electric potential on surface and morphology are crucial, as often designed by nature, for enhancing the water collection capabilities via the single-step production of fibers without any postprocessing needs