Comparative Study of PVDF Sheets and Their Sensitivity to Mechanical Vibrations: The Role of Dimensions, Molecular Weight, Stretching and Poling

From Brush to Dendritic Structure: Tool for Tunable Interfacial Compatibility between the Iron-Based Particles and Silicone Oil in Magnetorheological Fluids

Comprehensive magnetic particle stability together with compatibility between them and liquid medium (silicone oil) is still a crucial issue in the case of magnetorheological (MR) suspensions to guarantee their overall stability and MR performance. Therefore, this study is aimed at improving the interfacial stability between the carbonyl iron (CI) particles and silicone oil. In this respect, the particles were modified with polymer brushes and dendritic structures of poly(2-(trimethylsilyloxy)ethyl methacrylate) (PHEMATMS), called CI-brushes or CI-dendrites, respectively, and their stability properties (corrosion, thermo-oxidation, and sedimentation) were compared to neat CI ones. Compatibility of the obtained particles and silicone oil was investigated using contact angle and off-state viscosity investigation. Finally, the magneto-responsive capabilities in terms of yield stress and reproducibility of the MR phenomenon were thoroughly investigated. It was found that MR suspensions based on CI-brushes had significantly improved compatibility properties than those of neat CI ones; however, the CI-dendrites-based suspension possessed the best capabilities, while the MR performance was negligibly suppressed.

Advances in Wearable Piezoelectric Sensors for Hazardous Workplace Environments

Recent advances in wearable energy harvesting technology as solutions to occupational health and safety programs are presented. Workers are often exposed to harmful conditions-especially in the mining and construction industries-where chronic health issues can emerge over time. While wearable sensors technology can aid in early detection and long-term exposure tracking, powering them and the associated risks are often an impediment for their widespread use, such as the need for frequent charging and battery safety. Repetitive vibration exposure is one such hazard, e.g., whole body vibration, yet it can also provide parasitic energy that can be harvested to power wearable sensors and overcome the battery limitations. This review can critically analyze the vibration effect on workers' health, the limitations of currently available devices, explore new options for powering different personal protective equipment devices, and discuss opportunities and directions for future research. The recent progress in self-powered vibration sensors and systems from the perspective of the underlying materials, applications, and fabrication techniques is reviewed. Lastly, the challenges and perspectives are discussed for reference to the researchers who are interested in self-powered vibration sensors.

High Power Generation with Reducing Agents Using Compost Soil as a Novel Electrocatalyst for Ammonium Fuel Cells

Ammonium toxicity is a significant source of pollution from industrial civilization that is disrupting the balance of natural systems, adversely affecting soil and water quality, and causing several environmental problems that affect aquatic and human life, including the strong promotion of eutrophication and increased dissolved oxygen consumption. Thus, a cheap catalyst is required for power generation and detoxification. Herein, compost soil is employed as a novel electrocatalyst for ammonium degradation and high-power generation. Moreover, its effect on catalytic activity and material performances is systematically optimized and compared by treating it with various reducing agents, including potassium ferricyanide, ferrocyanide, and manganese dioxide. Ammonium fuel was supplied to the compost soil ammonium fuel cell (CS-AFC) at concentrations of 0.1, 0.2, and 0.3 g/mL. The overall results show that ferricyanide affords a maximum power density of 1785.20 mW/m2 at 0.2 g/mL fuel concentration. This study focuses on high-power generation for CS-AFC. CS-AFCs are sustainable for many hours without any catalyst deactivation; however, they need to be refueled at regular intervals (every 12 h). Moreover, CS-AFCs afford the best performance when ferricyanide is used as the electron acceptor at the cathode. This study proposes a cheap electrocatalyst and possible solutions to the more serious energy generation problems. This study will help in recycling ammonium-rich wastewaters as free fuel for running CS-AFC devices to yield high-power generation with reducing agents for ammonium fuel cell power applications.

Self-Poled Poly(vinylidene fluoride)/MXene Piezoelectric Energy Harvester with Boosted Power Generation Ability and the Roles of Crystalline Orientation and Polarized Interfaces

Micropiezoelectric devices have become one of the most competitive candidates for use in self-powered flexible and portable electronic products because of their instant response and mechanic-electric conversion ability. However, achievement of high output performance of micropiezoelectric devices is still a significant and challenging task. In this study, a poly(vinylidene fluoride) (PVDF)/MXene piezoelectric microdevice was fabricated through a microinjection molding process. The synergistic effect of both an intense shear rate (>10⁴ s^-1) as well as numerous polar C-F functional groups in MXene flakes promoted the formation of β-form crystals of PVDF in which the crystallinity of β-form could reach as high as 59.9%. Moreover, the shear-induced shish-kebab crystal structure with a high orientation degree (f_h = ∼0.9) and the stacked MXene acted as the driving force for the dipoles to regularly arrange and produce a self-polarizing effect. Without further polarization, the fabricated piezoelectric microdevices exhibited an open-circuit voltage of 15.2 V and a short-circuit current of 497.3 nA, under optimal conditions (400 mm s^-1 and 1 wt % MXene). Impressively, such piezoelectric microdevices can be used for energy storage and for sensing body motion to monitor exercise, and this may have a positive impact on next-generation smart sports equipment.