Faculty Publications

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Author: search.filters.author.Anandhan, S.Subject: search.filters.subject.Crystallinity

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    Durable, efficient, and flexible piezoelectric nanogenerator from electrospun PANi/HNT/PVDF blend nanocomposite
    (John Wiley and Sons Inc. cs-journals@wiley.com, 2019) Khalifa, M.; Mahendran, A.; Anandhan, S.
    Currently, there is considerable research focus on portable, lightweight, shock-resistant, and inexpensive wearable devices that are ideally powered by harvesting abundant mechanical or vibration energy, making battery or related wiring superfluous. In this study, piezoelectric nanogenerator was electrospun from PANi (polyaniline)/HNT (halloysite nanotube)/PVDF (poly[vinylidene fluoride]) blend nanocomposite. Polymorphism, crystallinity and morphology of the nanogenerator were explored in detail. HNT and PANi acted as a nucleating agent and conductive filler, respectively in PVDF; their synergism helps improve the piezoelectric performance of PVDF. The piezoelectric performance of the nanogenerator patch was studied under various external mechanical stresses, such as pressure, tapping, and impact. A maximum voltage output of approximately 7.2 V was generated by the nanogenerator under impact. The nanogenerator patch attached to human arm exhibited not only excellent piezoelectric response during arm movements, but, also proved to be flexible, highly sensitive and durable. This nanogenerator could possibly be used in wearable piezoelectric energy conversion application for self-powered devices. POLYM. COMPOS., 40:1663–1675, 2019. © 2018 Society of Plastics Engineers. © 2018 Society of Plastics Engineers
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    Polymorphism, dielectric and piezoelectric response of organo-modified Ni–Co layered double hydroxide nanosheets dispersed electrospun PVDF nanofabrics
    (Springer, 2019) Shetty, S.; Ekbote, G.S.; Mahendran, A.; Anandhan, S.
    Poly(vinylidene fluoride) (PVDF) with excellent flexibility and electroactive properties is a promising material for energy harvesting. In this study, organically modified Ni–Co layered double hydroxide (OLDH) was synthesized and the nanosheets of this OLDH were used as filler in electrospun PVDF nanofabrics. Morphology, crystallinity, dielectric, and piezoelectric properties of the electrospun nanofabrics were characterized. Presence of OLDH in PVDF nanofabrics led to enhancement of polar ?-phase in the latter, which was corroborated from the results of Fourier transform infrared spectroscopy and X-ray diffraction. Dielectric constant of the nanofabrics tends to increase with OLDH content, while the corresponding dielectric loss remained low. An indigenously designed nanogenerator from these nanofabrics exhibited a maximum output voltage of 6.9 V and power density of 0.92 ?W/cm2 under human finger tapping mode at 3 wt% loading of OLDH. The synergistic effect of OLDH and electrospinning contributed to the enhancement of the ?-phase content, thereby the piezoelectric response of the composite nanofabrics. The demonstrated nanogenerator could possibly power flexible and portable electronic devices. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.
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    Effect of polarization switching on piezoelectric and dielectric performance of electrospun nanofabrics of poly(vinylidene fluoride)/Ca–Al LDH nanocomposite
    (John Wiley and Sons Inc. P.O.Box 18667 Newark NJ 07191-8667, 2020) Shamitha, C.; Mahendran, A.R.; Anandhan, S.
    At present, highly flexible, durable, and lightweight piezoelectric nanogenerators with high-power density and energy conversion efficiency are of great interest. The present study reports a new synthetic route for Ca–Al layered double hydroxide (LDH) nanosheets and incorporation of these two-dimensional nanosheets as filler material into poly(vinylidene fluoride) (PVDF) to produce composite nanofabrics by electrospinning. The polymorphism, crystallinity, and the interaction between PVDF and LDH were studied by Fourier transform infrared spectroscopy, X-ray diffraction, and differential scanning calorimetry techniques. The synergetic effect of PVDF–LDH interaction and in situ stretching due to electrospinning facilitates the nucleation of electroactive ? phase up to 82.79%, which makes it a suitable material for piezoelectric-based nanogenerators. The piezoelectric performance of PVDF/Ca–Al LDH composite nanofabrics was demonstrated by hand slapping and frequency-dependent mechanical vibration mode, which delivered a maximum open circuit output voltage of 4.1 and 5.72 V, respectively. Moreover, the composite nanofabrics exhibited a high dielectric constant and low dielectric loss due to superior interfacial polarization at low-frequency region with LDH loading, promising its potential applications in electronic devices. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48697. © 2019 Wiley Periodicals, Inc.
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    Cationic surfactant assisted enhancement of dielectric and piezoelectric properties of PVDF nanofibers for energy harvesting application
    (Royal Society of Chemistry, 2021) Ekbote, G.S.; Khalifa, M.; Mahendran, A.; Anandhan, S.
    Poly(vinylidene fluoride) (PVDF) is among the most versatile polymers due to its wide range of properties, including dielectric, piezoelectric and ferroelectric properties. However, more frequently than not a range of processing routes and/or additives have been used to enhance such properties. In this study, PVDF nanofibers were electrospun from PVDF solution that contained tetra-n-butyl ammonium chloride (TBAC) at different loadings (1, 2, 3, and 5 wt%). The effect of TBAC on the morphology, crystallinity, and polymorphism of PVDF was studied using various characterization techniques. Addition of TBAC significantly improved the electroactive ?-phase of PVDF. The highest ?-phase content of 89% was attained at a TBAC loading of 3 wt%. Consequently, the dielectric and piezoelectric properties of the PVDF nanofibers improved significantly. A nanogenerator fabricated using 3 wt% TBAC/PVDF nanofibers exhibited the maximum voltage output of 17.2 V (under 5 N force) and the maximum power density of ?1.4 ?W cm?2(under 3 N force). Improved dielectric and piezoelectric properties of PVDF upon the addition of a small amount of TBAC could be useful for researchers in upbringing the material for flexible electronic devices. © The Royal Society of Chemistry 2021.
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    Influence of multiwalled carbon nanotubes on the structure and properties of poly(ethylene-co-vinyl acetate-co-carbon monoxide) nanocomposites
    (John Wiley and Sons Inc, 2021) George, G.; Mahendran, A.R.; SelvaKumar, S.; Anandhan, S.
    In this work, composites of poly(ethylene-co-vinyl acetate-co-carbon monoxide) (EVACO)/surface-modified multiwalled carbon nanotubes (m-MWCNTs) were prepared using a solution casting technique. Acid treatment was employed for the surface modification of MWCNTs to improve the compatibility between polar EVACO and MWCNTs. The influences of m-MWCNTs on the crystalline, mechanical, thermal, and electrical properties of EVACO at very low filler loading were systematically evaluated. The presence of m-MWCNTs in the EVACO matrix influenced the crystallinity, and the respective changes were determined and quantified using dynamic scanning calorimetry and X-ray diffraction. The mechanical properties of the composites were improved remarkably by the addition of a minute quantity (0.05, 0.1, 0.15, 0.2, and 0.25 wt%) of m-MWCNTs. Additionally, m-MWCNTs in the EVACO matrix improved the thermal stability and electrical properties of EVACO. However, the filler loading is below the threshold loading of the fillers, and there was no drastic improvement in the electrical conductivity of the composite. © 2021 Society of Plastics Engineers.
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    Physico-chemical and piezoelectric characterization of electroactive nanofabrics based on functionalized graphene/talc nanolayers/PVDF for energy harvesting
    (Springer Science and Business Media B.V., 2021) Shetty, S.; Shanmugharaj, A.M.; Anandhan, S.
    Poly(vinylidene fluoride) (PVDF) is a versatile polymer, whose dielectric, piezoelectric and ferroelectric properties can be augmented by a range of processing routes and/or additives. We developed a flexible nanogenerator using electrospun PVDF/COOH-functionalized graphene nanosheet (FGNS)/talc nanosheet (TNS) hybrid nanocomposites. TNS loading was fixed at 0.50 wt% while FGNS loading was varied (0.05, 0.10, 0.15, and 0.20 wt %) in these nanofabrics and their structure–property relationship was explored. Incorporation of FGNS led to formation of an electrically conductive network in the polymer matrix aided by TNS and electrospinning. The uniform dispersion of the filler nanosheets led to effective enhancement of the electroactive ?-phase of the PVDF matrix. Crystallinity and polymorphism in these systems were explored by FTIR spectroscopy, X-ray diffraction and differential scanning calorimetry. A nanogenerator made of the nanofabric containing 0.5 wt% of TNS and 0.10 wt% of FGNS was mechanically impacted by pneumatic actuator (operating pressure 0.4 MPa), resulting in an output voltage of 12.9 V and a power density of 1.72 µW/cm2, respectively. The piezoelectric coefficient (d33) of this nanofiber system was 61 pm/V as revealed by piezoelectric force microscopy. These novel nanocomposites could be used in flexible energy-harvesting devices. © 2021, The Polymer Society, Taipei.
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    A study on electroactive PVDF/mica nanosheet composites with an enhanced ?-phase for capacitive and piezoelectric force sensing
    (Royal Society of Chemistry, 2021) Khalifa, M.; Schoeffmann, E.; Lammer, H.; Mahendran, A.R.; Wuzella, G.; Anandhan, S.
    Herein, a multifunctional poly(vinylidene fluoride) (PVDF)/mica nanosheet composite (PMNC) thin film was developed for preparing a capacitive and piezoelectric force sensor. A high electroactive ?-phase content (89%) of PVDF was achieved through a facile rapid cooling process of PMNC films. The crystallinity of PVDF decreased upon the addition of mica nanosheets, while the dielectric constant increased significantly (?300%). The capacitance-based PMNC pressure sensor was found to be sensitive to the applied pressure. On the other hand, piezoelectric voltages of 18 V (single layer) and 32 V (multi-layer) were generated for PMNCs loaded with 1% mica nanosheets. Furthermore, a PMNC based nanogenerator generated a power density of 8.8 ?W cm?2and showed excellent durability (>60?000 cycles). High flexibility, lightweight and skin-friendly PMNCs could be a potential material in applications such as energy harvesting, energy storage, actuators, and self-powered and smart wearable electronic devices. © The Royal Society of Chemistry 2021.
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    Piezoelectric Energy Harvesting Using Flexible Self-Poled Electroactive Nanofabrics Based on PVDF/ZnO-Decorated SWCNT Nanocomposites
    (Springer, 2022) Khalifa, M.; Peravali, S.; Varsha, S.; Anandhan, S.
    This study probes the synergism of electrospinning and zinc oxide-decorated single-walled carbon nanotubes (ZCNT) in enhancing the β-phase nucleation and piezoelectric performance of PVDF. The nanofibers were spun in the form of nonwoven fabrics and characterized for their morphology, crystallinity, polymorphism, and tensile properties. Inclusion of ZCNT significantly promoted the β-phase (~95%) and tensile properties of PVDF, while the total degree of crystallinity was reduced. The highest voltage output of 15.5 V, which is 15 times more than that of the pristine PVDF nanofabrics, and a power density of 8.1 μWcm−2 was attained for the nanogenerator based on 0.75 wt.% ZCNT/PVDF nanofabrics. Implementation of electrospinning process and ZCNT proved to be beneficial in fabricating a flexible, lightweight, and robust nanogenerator for electronic devices. © 2022, The Minerals, Metals & Materials Society.
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    Development of a flexible piezoelectric and triboelectric energy harvester with piezo capacitive sensing ability from barium tungstate nanorod-dispersed PVDF nanofabrics
    (Institute of Physics, 2023) Ekbote, G.S.; Khalifa, M.; Venkatesa Perumal, B.; Anandhan, S.
    Lead-free flexible piezoelectric nanogenerator (PNG) and triboelectric nanogenerator (TENG) are sought after due to their ability to produce electricity by harnessing wasteful mechanical energy. A comprehensive understanding of additives and processing techniques is crucial for fine-tuning the performance of such energy systems. We have investigated in detail the effect of the addition of reverse microemulsion synthesized barium tungstate nanorods (BWN) on morphology, crystallinity, polymorphism of electrospun nanofabrics of poly(vinylidene fluoride) (PVDF). The electroactive phase content of the nanofabrics was enhanced upon the addition of BWN and the highest electroactive phase content of 86.5% was observed in the nanofabric containing 3 wt% of BWN. The dielectric constant of the nanofabric containing 5 wt% BWN was ∼1.96 times higher than that of pristine electrospun PVDF nanofabric (EPVDF). The ratio of relative change in the capacitance to initial capacitance of the sensor fabricated from the same system was ∼4 times greater than that of EPVDF. Consequently, its piezoelectric and triboelectric performances were improved. The PNG fabricated using the nanofabric containing 3 wt% BWN produced the highest open-circuit voltage of 8 V under an applied load of 8 N. A TENG made using the same system was able to produce a voltage output of 200 V, which was 1.77 times as high as that of EPVDF under one-finger tapping in contact-separation mode. The same composite nanofabric produced piezoelectric and triboelectric power densities of 4.3 µW cm−2 and 646 µW cm−2, respectively. The TENG was able to light 40 LEDs under one finger tapping. Fluttering-driven TENG fabricated using the aforementioned nanofabric was able to produce a triboelectric voltage of 84 V at a wind speed of 7 m s−1. Overall, these nanofabrics could be a potential material for energy harvesting devices for powering wearable devices, environmental sensors, and internet of things. © 2023 IOP Publishing Ltd
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    A Facile Strategy to Achieve High Piezoelectric Performance in Electrospun Poly(Vinylidene Fluoride) Non-woven Nanofabrics
    (Korean Institute of Electrical and Electronic Material Engineers, 2024) Khalifa, M.; Kumar, M.; Subramanian, G.; Anandhan, S.
    Poly(vinylidene fluoride) (PVDF) with its piezoelectric characteristics holds the potential to be the promising candidate in microdevices, sensors and actuators. In this study, a facile strategy was adopted to augment the electroactive β-phase of electrospun PVDF non-woven nanofabric. Electrospun PVDF non-woven fabric was mechanically stretched at different strain rates. SEM images revealed that upon stretching the non-woven fabric, the fibers tend to orient along the stretching direction. The fibers from the necked region were characterized to understand effect of stretching on the polymorphism, crystallinity and piezoelectric performance. The β-phase content of PVDF increased upon increasing the strain rate, while the degree of crystallinity decreased slightly. The highest β-phase content of 79% was achieved for electrospun PVDF non-woven fabric stretched at 10 mm/min. Further, the piezoelectric performance of the stretched nanofabric was evaluated to assess its electroactive characteristics. The piezoelectric performance of electrospun PVDF fabric was studied by imparting the pressure/load by one-finger tapping, hand pressure and dropping weight. The highest output voltage and current of 8.4 V and 249 nA, respectively were obtained from the electrospun PVDF non-woven stretched at 10 mm/min, which is almost 8 times higher than that of the unstretched PVDF non-woven. Given the flexibility, lightweight with good piezoelectric performance these electrospun PVDF non-woven fabrics could be a potential material for energy harvesting and self-powered nano-electronic devices. Graphical Abstract: (Figure presented.) © The Korean Institute of Electrical and Electronic Material Engineers 2023.