Anisotropic Impact Sensitivity of Metal-Free Molecular Perovskite High-Energetic Material (C6H14N2)(NH2NH3)(ClO4)3 by First-Principles Study.

Density functional theory simulations were carried out to investigate energetic molecular perovskite (C6H14N2)(NH2NH3)(ClO4)3 which was a new type energetic material promising for future application. The electronic properties, surface energy, and hydrogen bonding of (100), (010), (011), (101), (111) surfaces were studied, and the anisotropic impact sensitivity of these surfaces were reported. By comparing the values of the band gaps for different surface structures, we found that the (100) surface has the lowest sensitivity, while the (101) surface was considered to be much more sensitive than the others. The results for the total density of states further validated the previous conclusion obtained from the band gap. Additionally, the calculated surface energy indicated that surface energy was positively correlated with impact sensitivity. Hydrogen bond content of the surface structures showed distinct variability according to the two-dimensional fingerprint plots. In particular, the hydrogen bond content of (100) surface was higher than that of other surfaces, indicating that the impact sensitivity of (100) surface is the lowest.

Ion Transport in the EMITFSI/PVDF System at Different Temperatures: A Molecular Dynamics Simulation.

We used all-atom molecular dynamics simulations to study the ion transport in the 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide/poly(vinylidene fluoride) (EMITFSI/PVDF) system with 40.05 wt % EMITFSI at different temperatures. The glass-transition temperature (T g = 204 K) of this system shows a good agreement with the experimental value (200 K). With the increase of temperature, the peaks of the pair correlation function show an increasing trend. Interestingly, the coordination numbers of ion pairs and the degree of independent ion motion are mainly affected by the binding energy between ion pairs as the temperature increases. In addition, the ion transport properties with increasing temperature can be studied by the ion-pair relaxation times, ion-pair lifetimes, and diffusion coefficients. The simulation results illustrate that the ion transport is intensified. Especially, the cations can always diffuse faster than the anions. The power law shows that mobilities of anions and cations are seen to exhibit a "superionic" behavior. With the increase of temperature, transference numbers of anions decrease first and then increase and transference numbers of cations show the opposite changes; ionic conductivity increases gradually; and viscosity decreases gradually, indicating that the diffusion resistance of ions decreases. In general, after adding PVDF into the EMITFSI system, the glass-transition temperature and viscosity increase, the ionic conductivity and degree of independent ion motion decrease, and diffusion coefficients of cations decrease faster than those of the anions.

Power Generation from Moisture Fluctuations Using Polyvinyl Alcohol-Wrapped Dopamine/Polyvinylidene Difluoride Nanofibers.

Despite the boom in the water-triggered electric power generation technologies, few attempts have been made with a broader horizonyielding the electricity from sweat, which is of great value for low-power-consumption wearable electronics. Here, an electromechanical coupling and humidity-actuated two-in-one humidity actuator-driven piezoelectric generator (HAPG) are reported, that can yield continuous electric power from fluctuations in the ambient humidity. It is composed of polyvinyl alcohol (PVA)-wrapped highly aligned dopamine (DA)/polyvinylidene fluoride (PVDF) shell/core nanofibers (PVA@DA/PVDF NFs). As-received PVA@DA/PVDF NFs can exchange water with the ambient humidity to perform expansion and contraction and convert them into electric power. An all-fiber-based portable HAPG is fabricated and tested on human palm skin. The devices show high sensitivity and accuracy for converting the mental sweating-derived continuous moisture fluctuations into electric power. This electric power can be stored in capacitors, which is expected to power micro- and nano-electronic devices or be used in electrotherapy such as electrical stimulation to promote wound healing. Beyond this, the obtained voltage profiles exhibit unique features that can reflect the typical sweat damping oscillation curve features.

High-Performance Poly(vinylidene difluoride)/Dopamine Core/Shell Piezoelectric Nanofiber and Its Application for Biomedical Sensors.

Fabrication of soft piezoelectric nanomaterials is essential for the development of wearable and implantable biomedical devices. However, a big challenge in this soft functional material development is to achieve a high piezoelectric property with long-term stability in a biological environment. Here, a one-step strategy for fabricating core/shell poly(vinylidene difluoride) (PVDF)/dopamine (DA) nanofibers (NFs) with a very high ß-phase content and self-aligned polarization is reported. The self-assembled core/shell structure is believed essential for the formation and alignment of ß-phase PVDF, where strong intermolecular interaction between the NH2 groups on DA and the CF2 groups on PVDF is responsible for aligning the PVDF chains and promoting ß-phase nucleation. The as-received PVDF/DA NFs exhibit significantly enhanced piezoelectric performance and excellent stability and biocompatibility. An all-fiber-based soft sensor is fabricated and tested on human skin and in vivo in mice. The devices show a high sensitivity and accuracy for detecting weak physiological mechanical stimulation from diaphragm motions and blood pulsation. This sensing capability offers great diagnostic potential for the early assessment and prevention of cardiovascular diseases and respiratory disorders.

Core/Shell Piezoelectric Nanofibers with Spatial Self-Orientated ß-Phase Nanocrystals for Real-Time Micropressure Monitoring of Cardiovascular Walls.

Implantable pressure biosensors show great potential for assessment and diagnostics of pressure-related diseases. Here, we present a structural design strategy to fabricate core/shell polyvinylidene difluoride (PVDF)/hydroxylamine hydrochloride (HHE) organic piezoelectric nanofibers (OPNs) with well-controlled and self-orientated nanocrystals in the spatial uniaxial orientation (SUO) of ß-phase-rich fibers, which significantly enhance piezoelectric performance, fatigue resistance, stability, and biocompatibility. Then PVDF/HHE OPNs soft sensors are developed and used to monitor subtle pressure changes in vivo. Upon implanting into pig, PVDF/HHE OPNs sensors demonstrate their ultrahigh detecting sensitivity and accuracy to capture micropressure changes at the outside of cardiovascular walls, and output piezoelectric signals can real-time and synchronously reflect and distinguish changes of cardiovascular elasticity and occurrence of atrioventricular heart-block and formation of thrombus. Such biological information can provide a diagnostic basis for early assessment and diagnosis of thrombosis and atherosclerosis, especially for postoperative recrudescence of thrombus deep within the human body.