Phonon energy dissipation in friction between black phosphorus layers.

Herein, we employ molecular dynamics simulations to decode the friction properties and phonon energy dissipation between black phosphorus layers. The observations reveal the influence of three factors, temperature, velocity, and normal load, on the friction force of monolayer/bilayer black phosphorus. Specifically, friction is negatively correlated with layer thickness and temperature, and positively correlated with velocity and normal load. The change in friction force is further explained in terms of frictional energy dissipation, and supplemented by the height of potential barriers as well as the number of excited phonons. From the phonon spectrum analysis, the phonon number at the contact interface is found to be higher than that at the non-contact interface. This is due to the larger distance of the contact interface atoms deviate from their equilibrium positions, resulting in higher total energy generated by more intense oscillations, and therefore contributes greater to friction.

Coupling Effect of Structural Lubrication and Thermal Excitation on Phononic Friction.

This work investigates the coupling effect of structural lubrication and thermal excitation on phononic friction between black phosphorus (BP) layers. As the rotation angle increases from commensurate to incommensurate states, the friction gradually decreases at any temperature. However, the role of temperature in friction depends on commensurability. For a rotation angle less than 10°, increasing temperature leads to a decrease in friction due to thermal excitation. Conversely, when the rotation angle exceeds 10°, elevated temperature results in an increase in friction due to the effect of thermal collision. At a critical rotation angle of 10°, higher temperatures lead to reduced friction through thermal lubrication at low speeds, and at large speeds, the thermal excitation duration becomes so short that the role of thermal lubrication is weakened, and instead thermal collision dominates. Further research reveals that BP's ability to withstand different maximum speeds is also determined by commensurability. Finally, a method to measure the sliding period length of a rotated tip through an unrotated substrate potential energy topography is proposed and simply verified by using the phonon spectrum.

Ultrasound-assisted air-jet spinning of silk fibroin-soy protein nanofiber composite biomaterials.

Ultrasound utilizes a non-radiation technology that can meet modern standards to gain access to cheap, reliable and sustainable modern energy. Ultrasound technology can be implemented in the field of biomaterials for its exceptional potential in controlling the shape of nanomaterials. This study presents the first example of the production of soy and silk fibroin protein composite nanofibers in various ratios via combining ultrasonic technology with air-spray spinning. Characterization of ultrasonic spun nanofibers was performed by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric (TG) analysis, water contact angle, water retention, enzymatic degradation, and cytotoxicity assays. The effects that adjustments on the ultrasonic time have on the surface morphology, structures, thermal properties, hydrophilicity, water-uptake, bio-enzyme degradability, mechanical properties, and cytocompatibility of the material were examined. It was discovered that as the sonication time increased from 0 to 180 min, the beading phenomenon disappeared, forming nanofibers with uniform diameter and porosity; while the content of ß-sheet crystals in the composites and their thermal stability gradually increased, the materials glass transition temperature decreased, and preferred mechanical properties were obtained. Additional studies show that the hydrophilicity, water retention capacity and enzymatic degradation rate were also enhanced by ultrasound, providing a favorable environment for cell attachment and proliferation. This study highlights the experimental and theoretical methods for ultrasound assisted air-jet spinning of biopolymer nanofibrous materials with tunable properties and high biocompatibility, which provide a wide range of applications in wound dressings and drug-carrying systems. This work shows great potential for a direct road to sustainable development of protein based fibers in the industry, thus promoting economic growth, and improving the health of the general population and well-being of wounded patients worldwide.