Flexible materials with high electromechanical coupling performance are highly demanded for wide applications for electromechanical sensors and transducers, including mechanical energy harvesters. Here, outstanding electromechanical performance is obtained in electrospun‐aligned polyvinylidene fluoride (PVDF) fiber film. A theoretical model is developed from systematic theoretical analyses to clarify the underlying constructive piezoelectric‐triboelectric mechanism in the polarized PVDF fiber films that explains the experimental observations well. The electrospinning process induces polarization alignment and thus tunes the electron affinity for PVDF fibers with different polarization terminals, which results in the constructive piezoelectric and triboelectric responses in the obtained PVDF fiber films. Extremely large effective piezoelectric performance properties are achieved in the direct piezoelectric measurements, reaching the maximum effective piezoelectric strain and voltage coefficients of −1065 pm V−1 and −9178 V mm N−1, respectively, at 100 Hz. In the converse piezoelectric measurements without a significant contribution from reversible triboelectric effect, the maximum effective piezoelectric strain and voltage coefficients are −166 pm V−1 and −1499 V mm N−1, respectively. The theoretical analyses and experimental results show the great potential of the electrospun aligned polar PVDF fiber material for various electromechanical device applications, particularly for mechanical energy harvesting.

Many emerging applications strongly demand flexible and efficient electromechanical conversion materials. Polymeric piezoelectric materials, with ability of large area and low temperature processing, are attractive to obtain wide applications for electromechanical sensors, transducers, and mechanical energy harvesters. A major drawback of the polymeric piezoelectric materials is their much lower piezoelectric performance property, such as piezoelectric strain coefficient, than their ceramic counterparts. Here, outstanding piezoelectric performance properties with giant effective strain and voltage coefficients of −116 pm V−1 and −1180 V mm N−1 are achieved in electrospun polyvinylidene fluoride nanofiber films from the precursor solution modified with hydrated salt. The experimental results and theoretical analysis clarify a synergistic interactive role from the hydrated salt and the electric field during electrospinning, effectively leading to polarization enhancement and alignment, and hence the giant macroscopic piezoelectric coefficients in the obtained electrospun fiber films. The demonstrated results and the understanding on the underlying mechanism exhibit the potential and strategy in achieving high‐performance functional materials through dedicated control on their nanostructures and polarizations.

Distributed intelligence involving a large number of smart sensors and edge computing are highly demanded under the backdrop of increasing cyber-physical interactive applications including internet of things. Here, the progresses on ferroelectric materials and their enabled devices promising energy autonomous sensors and smart systems are reviewed, starting with an analysis on the basic characteristics of ferroelectrics, including high dielectric permittivity, switchable spontaneous polarization, piezoelectric, pyroelectric, and bulk photovoltaic effects. As sensors, ferroelectrics can directly convert the stimuli to signals without requiring external power supply in principle. As energy transducers, ferroelectrics can harvest multiple forms of energy with high reliability and durability. As capacitors, ferroelectrics can directly store electrical charges with high power and ability of pulse-mode signal generation. Nonvolatile memories derived from ferroelectrics are able to realize digital processors and systems with ultralow power consumption, sustainable operation with intermittent power supply, and neuromorphic computing. An emphasis is made on the utilization of the multiple extraordinary functionalities of ferroelectrics to enable material-critical device innovations. The ferroelectric characteristics and synergistic functionality combinations are invaluable for realizing distributed sensors and smart systems with energy autonomy.

Ramakrishna, S. (2018). Open-cell poly(vinylidene fluoride) foams with polar phase for enhanced airborne sound absorption. Applied Physics Letters, 113(9), 092903-.

Flexible and lightweight pressure sensors have attracted tremendous attention as a promising component of wearable biological motion sensors and artificial electronic skins. Here, the electromechanical response of as‐electrospun fiber mats composed of a commodity polymer, atactic polystyrene, which can be applied in low‐cost/large‐area, flexible, and lightweight pressure sensors is demonstrated. The fiber mat demonstrates a significantly high apparent converse piezoelectric constant of >30 000 pm V−1 under static measurement and ≈13 000 pm V−1 even at a high frequency of 1 kHz. The first theoretical model to explain the unique electromechanical response is constructed, which reveals that the softness and moderate charge of the fiber mat are the reasons for the significantly high electromechanical response. Further, apparent piezoelectric constants obtained by direct measurement are lower than those obtained by the converse measurement, which is attributed to the densification and hardening of the fiber mat due to prepressure applied in direct measurement. These findings are likely to serve as a milestone for the development of large‐area, flexible, and lightweight pressure sensors at low cost, as well as highly movable actuators like optical modulators without a substantial mechanical load.

Huge mechano-electrical performance obtained from net-like PVDF composites infiltrated with methylammonium lead iodide under vertical ultrasonic vibration, without additional poling.

Lead-free potassium and sodium niobate (KNN) nanofiber webs with random and aligned configurations were prepared by electrospinning process from polymer-modified chemical solution. The crystallization process, structure, composition, dielectric, ferroelectric and piezoelectric properties of the nanofibers and nanofiber webs were investigated. Theoretical analysis and experimental results showed that the surfaceinduced heterogeneous nucleation resulted in the remarkable lower crystallization temperature for the KNN nanofibers with {100} orientation of the perovskite phase in contrast to the bulk KNN gel, and thus wellcontrolled chemical stoichiometry. Low dielectric loss, large electric polarization, and high piezoelectric performance were obtained in the nanofiber webs. In particular, the aligned nanofiber web exhibited further improved piezoelectric strain and voltage coefficients, and higher FOM than their thin film counterparts, promising for high performance electromechanical sensors and transducers applications.

Dental caries is still the most prevalent chronic health condition in childhood. Dental care remains the most prevalent unmet health need, as 621 million children worldwide have untreated dental caries. 1 Despite the global prevalence of dental caries, only a few attempts have been made to investigate children's own accounts of how this condition affects their everyday lives. 2 Using oral health-related quality-of-life measures (OHRQoL), it has been established that the psychosocial, physical, and functional consequences of dental caries are often produced through acute infections, sleep deprivation, irritability, and difficulty in eating. 3 Furthermore, wider psychosocial impacts associated with smiling, schoolwork, and emotional and social well-being have been reported. 4 Although several measures for evaluating the impact of oral diseases on children's OHRQoL have been widely