Engineering Triboelectric Charge in Natural Rubber-Ag Nanocomposite for Enhancing Electrical Output of a Triboelectric Nanogenerator

Tannic Acid Modified Epoxidized Natural Rubber Based High Performing Triboelectric Nanogenerator

Considering today's environmental concerns, the development of triboelectric nanogenerator (TENG) is gaining immense interest as a green energy harvesting technology. However, most materials leveraged in TENG construction are based on non-renewable resources. Therefore, developing a bio-based composite with high performance for the TENG application is extremely desirable. This study uses Tannic acid (TA), a naturally occurring polyphenolic compound, as a reactive bio-filler in the bio-based elastomer Epoxidized natural rubber (ENR-50). This bio-composite is utilized as a tribo-positive pair for TENG construction, which resulted in a very high output voltage of 751 V (at 9 Hz) and 568 V (at 5 Hz). The maximum obtained power density recorded at 9 Hz is 37 W m-2 at 1 MΩ external load resistance and an average power density is 20 W m-2 at a load resistance of 10-100 MΩ. This excellent output performance results from the high electron-donating ability of TA. It is many-fold higher in terms of power density than recently reported all the bio-composites. Density Functional Theory is leveraged to probe contact electrification process. The result correlates with surface energy, dielectric, dynamic mechanical properties, and surface morphologies (roughness). Notably that such a bio-composite can be a promising material for next-generation power harvesting technology.

Skin-Inspired, Multifunctional, and 3D-Printable Flexible Sensor Based on Triple-Responsive Hydrogel for Signal Conversion in Skin Interface Electronics Health Management

Hydrogel-based flexible electronic components have become the optimal solution to address the rigidity problem of traditional electronics in health management. In this study, a multipurpose hydrogel is introduced, which is formed by combining a dual-network consisting of physical (chitosan, polyvinyl alcohol (PVA)) and chemical (poly(isopropyl acrylamide (NIPAM)-co-acrylamide (AM))) cross-linking, along with signal conversion fillers (eutectic gallium indium (EGaIn), Ti3C2 MXene, polyaniline (PANI)) for responding to external stimuli. Multiple sensing of dynamic and static signals is permissible for it. The strain sensor based on the hydrogel exhibits up to a 1000% resistance change within a 400% stretch range, and significant capacitance variations are observed upon touch. The temperature sensor yields a sensitivity of ≈-2.9% °C-1 at 20-40 °C and ≈65% °C-1 at 0-20 °C. The pH sensor responds with a sensitivity of near -13.68 mV pH-1. A paper-based triboelectric nanogenerator can be assembled to collect action energy at 83 mW m-2. The skin contact interface is kept in good condition owing to its 3D-printability, controllable antibacterial properties, along high cell survival rate. This multifunctional hydrogel holds promise in facilitating the integration of diagnosis and maintenance.

Enhanced Dielectric Properties and Antibacterial Activity of Natural Rubber by Modification with Poly(Acrylic Acid-Co-Acrylamide) Incorporating Silver Nanoparticles and Titanium Dioxide

This work aims to enhance natural rubber's dielectric properties and antibacterial activity by incorporating silver nanoparticles and titanium dioxide. Deproteinized natural rubber (DPNR) was modified through the graft copolymerization of acrylic acid and acrylamide using N', N'-Methylenebisacrylamide as a crosslinking agent, resulting in poly(acrylic acid-co-acrylamide)-modified, deproteinized natural rubber (MDPNR). This modification facilitated coordination with silver ions and interaction with titanium dioxide. Silver nanoparticles were generated under heat and pressure. Modified natural rubber composites containing silver nanoparticles and titanium dioxide (MDPNR/Ag-TiO2) were prepared. Scanning electron microscopy (SEM) revealed well-distributed silver in the modified natural rubber matrix, while agglomeration of titanium dioxide was observed at a high loading. Both MDPNR and MDPNR/Ag-TiO2 showed high thermal stability compared to DPNR. The MDPNR/Ag-TiO2 composites exhibited higher Tg and lower tan δ, indicating higher stiffness due to the restriction of chain movement compared to that in MDPNR. DPNR exhibited a low dielectric constant, enhanced by poly(acrylic acid-co-acrylamide) modification and silver nanoparticle/titanium dioxide incorporation. Incorporating 0.5 phr of AgNO3 and 2.5 phr of TiO2 in the composites increased the dielectric constant by 1.33 times compared to that of MDPNR. MDPNR showed no antibacterial activity, while the MDPNR/Ag-TiO2 composites exhibited promising antibacterial activity against Staphylococcus aureus and Escherichia coli.

Graphene-Infused Sustainable Rubber-Based Triboelectric Nanogenerator For Real-Time Human Motion Monitoring

Triboelectric nanogenerators (TENG) are promising alternatives for clean energy harvesting. However, the material utilization in the development of TENG relies majorly on polymers derived from non-renewable resources. Therefore, minimizing the carbon footprint associated with such TENG development demands a shift toward usage of sustainable materials. This study pioneers using natural rubber (NR) as a sustainable alternative in TENG development. Infusing graphene in NR, its dielectric constant and tribonegativity are optimized, yielding a remarkable enhancement. The optimized sample exhibits a dielectric constant of 411 (at 103 Hz) and a contact potential difference (CPD) value of 1.85 V. In contrast, the pristine NR sample showed values of 6 and 3.06 V for the dielectric constant and CPD. Simulation and experimental studies fine-tune the TENG's performance, demonstrating excellent agreement between theoretical predictions and practical studies. Sensors developed via stencil printing technique possess a remarkably low layer thickness of 270 µm, and boast a power density of 420 mW m-2, a staggering 250% increase over conventional NR. Moreover, the material is pressure sensitive, enabling precise real-time human motion detection, including finger contact, finger bending, neck bending, and arm bending. This versatile sensor offers wireless monitoring, empowering healthcare monitoring based on the Internet of Things.

Electrostatic energy-driven contact electrification mechanism from the ReaxFF molecular dynamics perspective

Understanding the underlying principles of contact electrification is critical for more efficient triboelectric nanogenerator (TENG) development. Herein, we use ReaxFF molecular dynamics simulations in conjunction with a charge equilibration method to investigate the contact electrification mechanism in polyisoprene (PI), a natural rubber polymer, when it comes into contact with copper (Cu) and polytetrafluoroethylene (PTFE). The simulations reveal that the charge transfer directions in the PI/Cu and PI/PTFE contact models are opposite, and the amount of charge transfer in the former is substantially less than that in the latter, which are consistent with our TENG measurements. Contact electrification is revealed to be a spontaneous process that occurs to lower electrostatic energy, and the electrostatic energy released during contact electrification of PI/PTFE is greater than that of PI/Cu, which can be correlated with the relative strength of triboelectric charging observed for the two systems. A compression simulation of the PI/Cu contact model reveals that the quantity of charge transfer grows exponentially as compressive strain increases. Despite increasing the total energy of the system due to densification and distortion of the polymer structure, the applied deformation results in an energetically more stable electrostatic arrangement. We also find that the incorporation of a carbonaceous material into a polyisoprene matrix causes a faster increase in the amount of charge transfer with compressive strain, which is governed by a steeper electrostatic energy profile. This study provides an alternative perspective on the contact electrification mechanism, which could be beneficial for the development of energy harvesting devices.

Wearable, Machine Washable, Breathable Polyethylenimine/Sodium Alginate Layer-by-Layer-Coated Cotton-Based Multifunctional Triboelectric Nanogenerators

Cotton-based textiles are ubiquitous in daily life and are prime candidates for application in wearable triboelectric nanogenerators. However, pristine cotton is vulnerable to bacterial attack, lacks antioxidant and ultraviolet (UV)-protective abilities, and shows lower triboelectric charge generation against tribonegative materials because it is present in the neutral region of the triboelectric series. To overcome such drawbacks, herein, a facile layer-by-layer method is proposed, involving the deposition of alternate layers of polyethylenimine (PEI) and sodium alginate (SA) on cotton. Such modified fabric remains breathable and flexible, retains its comfort properties, and simultaneously shows multifunctionalities and improved triboelectric output, which are retained even after 50 home laundering cycles. Also, the modified fabric becomes more tribopositive than nylon, silk, and wool. A triboelectric nanogenerator consisting of modified cotton and polyester fabric is proposed that shows a maximum power density of 338 mW/m2. An open-circuit voltage of ∼97.3 V and a short-circuit current of ∼4.59 μA are obtained under 20 N force and 1 Hz tapping frequency. Further, the modified cotton exhibits excellent antibacterial, antioxidant, and UV-protective properties because of the incorporation of PEI, and its moisture management properties are retained due to the presence of sodium alginate in the layer. This study provides a simple yet effective approach to obtaining durable multifunctionalities and improved triboelectric performance in cotton substrates.

Using Natural Dye Additives to Enhance the Energy Conversion Performance of a Cellulose Paper-Based Triboelectric Nanogenerator

Green and sustainable power sources for next-generation electronics are being developed. A cellulose paper-based triboelectric nanogenerator (TENG) was fabricated to harness mechanical energy and convert it into electricity. This work proposes a novel approach to modify cellulose paper with natural dyes, including chlorophyll from spinach, anthocyanin from red cabbage, and curcumin from turmeric, to enhance the power output of a TENG. All the natural dyes are found to effectively improve the energy conversion performance of a cellulose paper-based TENG due to their photogenerated charges. The highest power density of 3.3 W/m2 is achieved from the cellulose paper-based TENG modified with chlorophyll, which is higher than those modified with anthocyanin and curcumin, respectively. The superior performance is attributed not only to the photosensitizer properties but also the molecular structure of the dye that promotes the electron-donating properties of cellulose.

The Modification of Activated Carbon for the Performance Enhancement of a Natural-Rubber-Based Triboelectric Nanogenerator

Increasing energy demands and growing environmental concerns regarding the consumption of fossil fuels are important motivations for the development of clean and sustainable energy sources. A triboelectric nanogenerator (TENG) is a promising energy technology that harnesses mechanical energy from the ambient environment by converting it into electrical energy. In this work, the enhancement of the energy conversion performance of a natural rubber (NR)-based TENG has been proposed by using modified activated carbon (AC). The effect of surface modification techniques, including acid treatments and plasma treatment for AC material on TENG performance, are investigated. The TENG fabricated from the NR incorporated with the modified AC using N2 plasma showed superior electrical output performance, which was attributed to the modification by N2 plasma introducing changes in the surface chemistry of AC, leading to the improved dielectric property of the NR-AC composite, which contributes to the enhanced triboelectric charge density. The highest power density of 2.65 mW/m2 was obtained from the NR-AC (N2 plasma-treated) TENG. This research provides a key insight into the modification of AC for the development of TENG with high energy conversion performance that could be useful for other future applications such as PM2.5 removal or CO2 capture.

Synthetic Polyisoprene Rubber as a Mimic of Natural Rubber: Recent Advances on Synthesis, Nanocomposites, and Applications

Up to now, rubber materials have been used in a wide range of applications, from automotive parts to special-design engineering pieces, as well as in the pharmaceutical, food, electronics, and military industries, among others. Since the discovery of the vulcanization of natural rubber (NR) in 1838, the continuous demand for this material has intensified the quest for a synthetic substitute with similar properties. In this regard, synthetic polyisoprene rubber (IR) emerged as an attractive alternative. However, despite the efforts made, some properties of natural rubber have been difficult to match (i.e., superior mechanical properties) due not only to its high content of cis-1,4-polyisoprene but also because its structure is considered a naturally occurring nanocomposite. In this sense, cutting-edge research has proposed the synthesis of nanocomposites with synthetic rubber, obtaining the same properties as natural rubber. This review focuses on the synthesis, structure, and properties of natural and synthetic rubber, with a special interest in the synthesis of IR nanocomposites, giving the reader a comprehensive reference on how to achieve a mimic of NR.

Design and Fabrication of Polymer Triboelectric Nanogenerators for Self-Powered Insole Applications

Triboelectric nanogenerators (TENGs) are a kind of mechanical energy harvester with a larger force sensing range and good energy conversion, which is often applied to human kinetic energy collection and motion sensing devices. Polymer materials are the most commonly used materials in TENGs' triboelectric layers due to their high plasticity and good performance. Regarding the application of TENGs in insoles, research has often used brittle Teflon for high output performance together with hard materials, such as springs, for the mechanism to maintain its stability. However, these combined materials increase the weight and hardness of the insoles. Here, we propose a polyethylene terephthalate (PET)-based TENG with a micro-needle polydimethylsiloxane (PDMS) elastomer, referred to as MN-PDMS-TENG, to enhance performance and maintain comfort flexibility, and structural stability. Compared with a flat PDMS, the TENG with a microstructure enhances the output open-circuit voltage (Voc) from 54.6 V to 129.2 V, short-circuit current (Isc) from 26.16 μA to 64.00 μA, power from 684 µW to 4.1 mW, and ability to light up from 70 to 120 LEDs. A special three-layer TENG insole mechanism fabricated with the MN-PDMS-TENG and elastic materials gives the TENG insole high stability and the ability to maintain sufficient flexibility to fit in a shoe. The three-layer TENG insole transforms human stepping force into electric energy of 87.2 V, which is used as a self-powered force sensor. Moreover, with the calibration curve between voltage and force, it has a sensitivity of 0.07734 V/N with a coefficient of determination of R2 = 0.91 and the function between force and output voltage is derived as F = 12.93 V - 92.10 under human stepping force (300~550 N). Combined with a micro-control unit (MCU), the three-layer TENG insole distinguishes the user's motion force at different parts of the foot and triggers a corresponding device, which can potentially be applied in sports and on rehabilitation fields to record information or prevent injury.

Ag-Cellulose Hybrid Filler for Boosting the Power Output of a Triboelectric Nanogenerator

The triboelectric nanogenerator (TENG) is a newly developed energy harvesting technology that can convert mechanical energy into electricity. The TENG has received extensive attention due to its potential applications in diverse fields. In this work, a natural based triboelectric material has been developed from a natural rubber (NR) filled with cellulose fiber (CF) and Ag nanoparticles. Ag nanoparticles are incorporated into cellulose fiber (CF@Ag) and are used as a hybrid filler material for the NR composite to enhance the energy conversion efficiency of TENG. The presence of Ag nanoparticles in the NR-CF@Ag composite is found to improve the electrical power output of the TENG by promoting the electron donating ability of the cellulose filler, resulting in the higher positive tribo-polarity of NR. The NR-CF@Ag TENG shows significant improvement in the output power up to five folds compared to the pristine NR TENG. The findings of this work show a great potential for the development of a biodegradable and sustainable power source by converting mechanical energy into electricity.