Browsing by Author "Lammer, H."

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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.
Ionic Surfactant-Assisted PVDF Nanofabrics with High Dielectric and Excellent Piezoelectric Performance
(Korean Fiber Society, 2024) Khalifa, M.; Lammer, H.; Anandhan, S.
Flexible dielectrics and piezoelectric sensors have attracted a number of applications in advanced electronic systems. In this regard, poly(vinylidene fluoride) (PVDF) is considered as a promising option due to its flexibility and ferroelectric properties. In this study, a highly flexible non-woven fabric was developed from electrospun PVDF nanofibers containing cationic and anionic surfactants. Cetrimonium bromide (CTAB) was used as a cationic surfactant, while sodium lauryl sulfate (SLS) was used as an anionic surfactant. The presence of cationic and anionic surfactants played a pivotal role in the production of finer fibers. PVDF-SLS nano-fabric exhibited oriented fibers, while PVDF-CTAB nano-fabric displayed randomly arranged fibers. PVDF-SLS-based nano-fabric displayed the highest β-phase content of 98.2%, while PVDF-CTAB non-woven showed a β-phase content of 91.6%. A significant improvement in the dielectric properties of PVDF nano-fabric was observed upon the addition of cationic and anionic surfactants. Furthermore, PVDF-SLS nano-fabric demonstrated exceptional dielectric and piezoelectric properties, generating a piezoelectric voltage of ~ 19 V. In comparison, PVDF-CTAB nano-fabric exhibited a piezoelectric voltage of 12.5 V. The power density of PVDF improved significantly upon the addition of SLS surfactant. Such attributes position PVDF-SLS nanofabrics as valuable candidates for diverse applications, particularly in the field of piezoelectric sensors and energy storage devices. The research not only advances the understanding of optimizing PVDF nanofabrics, but also establishes a foundation for future exploration in the realm of flexible electronics. Graphical Abstract: (Figure presented.) © The Author(s), under exclusive licence to the Korean Fiber Society 2024.
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.