Journal Articles
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Item Probing the synergism of halloysite nanotubes and electrospinning on crystallinity, polymorphism and piezoelectric performance of poly(vinylidene fluoride)(Royal Society of Chemistry, 2016) Khalifa, M.; Mahendran, A.; Anandhan, S.Poly(vinylidene fluoride) (PVDF) nanofibers have tremendous potential in nano-sensing and energy scavenging applications. In this study, uniaxially aligned nanofibers were developed from halloysite nanotubes (HNT)/PVDF nanocomposite using electrospinning technique. Incorporation of HNT into PVDF not only reduced the diameter of the electrospun nanofibers, but, also improved their morphology. Fourier transform infrared spectroscopy, wide angle X-ray diffraction and differential scanning calorimetry techniques were used to characterize the crystallinity, polymorphism and polymer-filler interaction in the nanocomposite nanofibers. A force sensor was indigenously designed to study the piezoelectric responses of the nanocomposite nanofibers. At 10 wt% of HNT loading, the sensor produced the highest voltage output, which can be ascribed to its highest ?-phase content. Incorporation of HNT and use of electrospinning synergistically enhanced the ?-phase content and hence the piezoelectric behavior of PVDF. Hence, these nanofibers could be promising and prominent materials in sensor and actuator applications. © The Royal Society of Chemistry.Item Synergism of Electrospinning and Nano-alumina Trihydrate on the Polymorphism, Crystallinity and Piezoelectric Performance of PVDF Nanofibers(Minerals, Metals and Materials Society 184 Thorn Hill Road Warrendale PA 15086, 2018) Khalifa, M.; Deeksha, B.; Mahendran, A.; Anandhan, S.Poly(vinlylidene fluoride) (PVDF) is known for its electroactive phases, which can be nucleated by incorporating nanoparticles into PVDF to enhance its piezoelectric performance. In this study, the synergistic effect of electrospinning and nano alumina trihydrate (ATH) filler was used to enhance the electroactive ? phase of PVDF. Electrospun nanofibers of PVDF/ATH nanocomposite (PANCF) were synthesized with different loadings of ATH. The presence of ATH enhances the surface charges of the electrospun droplets, leading to thinner fibers. The highest ?-phase content was found to be 70.1% for PANCF with 10% ATH. The piezoelectric performance of the nanofiber mats was studied using an indigenous setup. The highest voltage output of 840 mV was produced by PANCF with 10% ATH. These nanofibers could be a promising material in the field of sensors, actuators and energy-harvesting applications. © 2018, The Minerals, Metals & Materials Society.Item Synergism of graphitic-carbon nitride and electrospinning on the physico-chemical characteristics and piezoelectric properties of flexible poly(vinylidene fluoride) based nanogenerator(Springer Netherlands rbk@louisiana.edu, 2019) Khalifa, M.; Mahendran, A.; Anandhan, S.Herein, we investigated the piezoelectric performance of electrospun poly(vinylidene fluoride)/graphitic carbon nitride (PVDF/g-C 3 N 4 ) nanocomposite fibers (PGN-X). Addition of g-C 3 N 4 nanosheets improved the spinnability of nanofibers and augmented the ?-phase content of PVDF. The synthesized PGN non-woven mats were flexible and easily deformable without disrupting the continuity of fibers. Upon the addition of g-C 3 N 4 , tensile strength and thermal stability of nanocomposite fibers improved significantly. A maximum voltage output of ~7.5 V was generated for PGN nanogenerator which is ~8 times more than that of PVDF nanogenerator. Also, the PGN-X nanogenerator generated current output of 0.23 ?A and a power density of 0.22 ?W/cm ?2 . Improved physico-chemical characteristics and piezoelectric performance of PGN nanogeneratoris promising and makes it suitable for portable electronic and wearable devices. © 2019, The Polymer Society, Taipei.Item 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 EngineersItem PVDF/halloysite nanocomposite-based non-wovens as gel polymer electrolyte for high safety lithium ion battery(John Wiley and Sons Inc. cs-journals@wiley.com, 2019) Khalifa, M.; Janakiraman, S.; Ghosh, S.; Adyam, A.; Anandhan, S.Gel polymer electrolyte (GPE) based on electrospun poly(vinylidene fluoride) (PVDF)/halloysite nanotube (HNT) nanocomposite non-wovens was synthesized and its suitability as a separator in lithium-ion battery (LIB) was explored. In this study, HNT played a key role in reducing the average diameter of the electrospun fibers and uplifted the porosity of the non-wovens thereby improving their electrolyte uptake. Due to a reduction in crystallinity and increased % porosity of the PVDF/HNT non-wovens, the ionic conductivity (1.77 mScm?1) and ionic transport across the separator were improved. Moreover, this GPE separator exhibited high tensile and puncture strength with negligible thermal shrinkage and a higher melting temperature compared with a commercially available separator, which is vital from the safety perspective. The cycling performance of Li/GPE/LiCoO2 cell was evaluated and it exhibited a high capacity of 138.01 mAhg?1 with 97% coulombic efficiency for the initial cycle. The cell was stable and retained its high performance with little loss in capacity even after repeated charge–discharge cycles. Such a combination of high ionic conductivity, tensile strength with low thermal shrinkage is seen to be very rare in polymer-based separators. It is noteworthy that this novel GPE outperformed the commercial separator also in the cycle performance. POLYM. COMPOS., 40:2320–2334, 2019. © 2018 Society of Plastics Engineers. © 2018 Society of Plastics EngineersItem An electroactive ?-phase polyvinylidene fluoride as gel polymer electrolyte for magnesium–ion battery application(Elsevier B.V., 2019) Singh, R.; Janakiraman, S.; Khalifa, M.; Anandhan, S.; Ghosh, S.; Adyam, A.; Biswas, K.The gel polymer electrolytes (GPEs) are currently interesting research area in rechargeable batteries. In the present study, synthesis and characterization of electroactive gel polymer electrolyte (EGPE) for Mg-ion batteries application have been investigated. The bead free electroactive polyvinylidene fluoride (PVDF) with high porosity is achieved by an electrospinning process. The ?-phase of PVDF is polar and electroactive with a high dipole moment. Electroactive ?-phase is confirmed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Field emission scanning electron microscopy (FESEM) study is done to analyze the structure and morphology of the electroactive membrane. The electroactive gel polymer electrolyte is formed by immersing an electroactive PVDF membrane in 0.3 M magnesium perchlorate (MgClO4) and propylene carbonate (PC) solution. The ionic conductivity of electroactive ?-phase PVDF membrane is achieved to be 1.49 mS cm?1 at 30 °C, which is higher than commercial available polypropylene (PP) Celgard. Tortuosity of electroactive gel polymer electrolyte is found to be 1.44. The voltage stability of the EGPE is stable up to a high voltage of 5.0 V against Mg+2/Mg. The total ionic transference number and magnesium ion transference number of EGPE are also investigated to confirm high ionic conductivity. © 2019 Elsevier B.V.Item PVDF Nanofibers with Embedded Polyaniline-Graphitic Carbon Nitride Nanosheet Composites for Piezoelectric Energy Conversion(American Chemical Society service@acs.org, 2019) Khalifa, M.; Anandhan, S.Herein, a facile approach was used to synthesize an ultrasensitive, durable, and flexible electrospun poly(vinylidene fluoride) (PVDF)/polyaniline (PANI)/graphitic carbon nitride nanosheets (g-C3N4) blend nanocomposite fibers (PPBF) based piezoelectric nanogenerator. PANI/g-C3N4 nanocomposite (PGNC) was prepared prior to its dispersal in PVDF. This unpretentious synthesis approach exploited the ?-nucleating activity of g-C3N4 along with the enhancement of electrical conductivity due to a network of PANI within individual PVDF nanofibers. Addition of PGNC and electrospinning synergistically enhanced the ?-phase content (?97%) of PVDF. The PPBF nanogenerator displayed remarkable improvement in the voltage and current output compared to pristine PVDF nanofibers (?1300%). The nanogenerator generated a voltage output of ?30 V and current output of 3.7 ?A with high stability and reproducibility (>50※000 cycles). The PPBF nanogenerator exhibited high-power density and conversion efficiency and was able to light up 70 commercial LEDs. The newly developed high performance nanogenerator could be a potential material in smart, self-powered wearable devices. © 2019 American Chemical Society.Item Physicochemical characteristics of bio-based thermoplastic polyurethane/graphene nanocomposite for piezoresistive strain sensor(John Wiley and Sons Inc. P.O.Box 18667 Newark NJ 07191-8667, 2020) Khalifa, M.; Ekbote, G.S.; Anandhan, S.; Wuzella, G.; Lammer, H.; Mahendran, A.R.Herein, we report the physicochemical characteristics and piezoresistive strain sensing performance of flexible thin film comprising graphene and bio-based thermoplastic polyurethane (TPU) prepared by solution cast method. A detailed analysis was carried to study the influence of graphene nanoplatelets on the morphological, thermal, mechanical, and electrical properties of TPU nanocomposite. Upon increasing the graphene nanoplatelets loading, the thermal stability and tensile properties improved remarkably, while glass transition temperature decreased slightly. Owing to better dispersion of graphene, the electrical conductivity was significantly increased, which broaden the utilization of the nanocomposite for various applications. The piezoresistive sensor was able to respond to various stress modes such as tapping, bending, and finger touch. The piezoresistive sensor was sensitive and achieved a gauge factor of 11. Sensor attached to finger, showed distinctive response upon bending at different angles and showed high stability and reproducibility even after >10,000 cycles under repetitive constant load. Also, the nanocomposite was able to detect any breakage or fracture in the form of change in electrical resistance. A combination of bio-based TPU and graphene offered improved physical properties and high sensing performance, which could be a potential material in flexible electronics and structural health monitoring systems. © 2020 Wiley Periodicals, Inc.Item A high thermally stable polyacrylonitrile (PAN)-based gel polymer electrolyte for rechargeable Mg-ion battery(Springer, 2020) Singh, R.; Janakiraman, S.; Khalifa, M.; Anandhan, S.; Ghosh, S.; Adyam, A.; Biswas, K.The ionic conductivity and thermal stability of the electrolyte-separator system is an essential parameter for improving battery performance and safety. The present work addresses the high thermally stable gel polymer electrolyte (GPE) using polyacrylonitrile (PAN) as a polymer membrane and magnesium perchlorate in propylene carbonate (Mg(ClO4)2-PC) as a liquid electrolyte. The PAN based polymer membrane is prepared by electrospinning process which produces a bead free and uniformly distributed nanofibers. The electrospun PAN based GPE is characterized by different physical and electrochemical techniques like X-ray diffraction, field emission scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, ionic conductivity, linear sweep voltammetry, magnesium ion transference number and electrochemical impedance spectroscopy. The ionic conductivity of PAN is 3.28 mS cm?1, compared to that of PP Celgard is 1.97 × 10–4 mS cm?1 at 30 °C. The electrochemical stability of PAN is 4.6 V and also exhibits excellent interfacial stability with magnesium metal. The results showed that the PAN-based GPE has higher ionic conductivity and thermal stability than the polypropylene (PP) Celgard membrane. © 2020, Springer Science+Business Media, LLC, part of Springer Nature.Item 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.