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With the ever-decreasing size of portable electronics to achieve greater versatility, the power density of electronic devices has increased substantially, to the point where efficient cooling has become a major concern for achieving stable device operation. Herein, we introduce a heat-dissipating film coated with carbon nanotubes (CNTs) entangled with silver nanowires (AgNWs), prepared by supersonic spraying. Low thermal resistance was obtained from the strong adhesion between the deposited nanomaterials and the substrate. The optimal hybrid film for achieving maximal cooling was identified by varying the number of spraying sweeps and the composition of the nanomaterials. The hybrid film, comprising both CNTs and AgNWs, afforded superior cooling owing to its improved thermal conductivity. Surface-texturing of the film also significantly impacted the convective-cooling performance. In addition, the superior heat-spreading capability of the hybrid film was demonstrated by comparing infrared images of the bare substrate, pure CNTs, and hybrid CNT/AgNW films. The wettability of these films was also studied to identify the wetting condition that would provide the maximum heat transfer. The hybrid CNT/AgNW film possessed the most hydrophilic surface, providing the most efficient spray-cooling scenario. The hydrophilic surface captured and held the sprayed droplets firmly throughout the process. Hence, these CNT/AgNW hybrid films represent a commercially viable solution for addressing hotspots in portable electronic devices. [ABSTRACT FROM AUTHOR]

In the present work, aqueous solutions of NaPAA [poly (sodium acrylate)] or PAA [polyacrylic acid] are used as the coolants for a dental handpiece to evaluate their suppressive effect on the aerosolization and bacteria (Staphylococcus epidermidis) transmission in an actual dental environment. Both polymer solutions significantly suppressed the formation of aerosols (<50 μm) and droplets (50–100 μm). The suppression effect was stronger at higher concentrations. The 10 and 20 wt. % of viscous Newtonian solutions of low-molecular weight NaPAA were much less effective in disintegration suppression than the viscoelastic 1 and 2 wt. % PAA solutions. The latter was capable of complete suppression of disintegration, forming instead long liquid threads attached to the rotating bur and settling down underneath. The suppression efficiency of the 2 wt. % PAA solution stems from significant elastic forces in it which prevent drop detachment. In the case of water used as a coolant, the bacterial spread was observed through aerosol, droplets, and splatter. The bacterial spread by large splatters was inversely proportional to the distance from the rotating bur. The spread of aerosols significantly occurred in the direction that the handpiece was facing, and multiple airborne aerosols settled on the wall rather than on the floor. On the other hand, the viscoelastic aqueous 2 wt. % PAA solution suppressed bacterial spread, regardless of the distance or direction. [ABSTRACT FROM AUTHOR]

Cooling liquids used in ultrasonic scalers are aerosolized into droplets. Larger droplets splatter over dental practitioners and patients, and small aerosols become airborne, posing a health threat to people in the surrounding area if a patient is infected by viral or bacterial infections. Polyacrylic acid (PAA), polyethylene glycol (PEG), and polyvinylpyrrolidone (PVP) can efficiently cool teeth and suppress aerosolization owing to their rheological properties, with PAA being the superior viscoelastic suppressant. Although the solutions of PEG and PVP studied here are also efficient in suppressing aerosol formation, their high viscosity may hinder their supply to the dental tools because of high viscous dissipation. The rheological behavior of PAA, PEG, and PVP is studied in the uniaxial elongational flow in self-thinning capillary threads. Then, the behavior of these solutions in an ultrasonic scaler in dental practice is explored. In particular, the aerosolization phenomena and the corresponding aerosol size distributions and droplet trajectories are studied and compared. The tooth temperature is found to be similar to that of water when these polymer solutions are used. The dispersion of the aerosolized droplets is qualitatively demonstrated by performing scaling using model teeth on a phantom mannequin face. [ABSTRACT FROM AUTHOR]

Aerosolized droplets are produced en masse in dental practices; these aerosols disperse in the surrounding space, posing a health threat if the patient is infected with a transmittable disease, particularly COVID-19. Here, a viscoelastic polyacrylic acid (PAA) solution was used to minimize liquid aerosolization and limit the travel distance of aerosols. The PAA concentration was varied to evaluate its effect on aerosolization and droplet size resulting from procedures using dental handpieces, which include tooth cutting, grinding, and polishing. In addition, a thermocouple was inserted at the center of the model tooth to measure its temperature during a handpiece operation. The temperature data suggest that the cooling performance of the PAA solution is comparable to that of pure water in operations in the occlusal and facial directions. The PAA solution droplets splattered on the patient's facial area during the handpiece operation are markedly larger than those of pure water, which is evidence of the settling of the PAA droplets, preventing further transmission. Accordingly, the travel distance of the aerosolized PAA droplets was limited by viscoelastic resistance to droplet detachment. This comparison of the aerosol suppression capability between water and PAA solutions confirms the benefit of using viscoelastic solutions for various dental operations. [ABSTRACT FROM AUTHOR]

Piezoelectricity, flexibility, light weight, and biocompatibility of piezoelectric polymer fibers are the desired attributes for energy harvesting and sensing in wearable and biomedical applications. However, the relatively insufficient piezoelectric performance of piezoelectric polymers remains an issue. Here, we demonstrate a considerable increase in P(VDF-TrFE) fiber alignment via electrospinning with a rapidly rotating collector, which substantially enhanced the piezoelectric performance of the fiber mat over a large area. Considering the relationship between the airflow induced near the collector surface and the rotating speed, the collectors with different geometries were systematically compared in terms of the degree of alignment, fiber morphology, and the resulting crystalline electroactive phases of the fibers produced by each collector. We found that the strong airflow induced by the rapid rotation of the modified drum collector contributes to the preferential fiber orientation by pulling and stretching over a large area, which led to an increase in the crystalline electroactive β-phase content responsible for piezoelectricity. As a result, a maximum voltage of 116.6 V and maximum output power of 13.6 µW were achieved using a flexible piezoelectric device comprising a large-area, highly aligned P(VDF-TrFE) fiber mat produced from a modified drum collector at a significantly high speed. This work provides a facile but powerful solution for the wide use of piezoelectric polymer fibers. [ABSTRACT FROM AUTHOR]

Electrospun piezoelectric polymer fibers, which offer mechanical flexibility, light weight, and relatively low temperature processing, have emerged as a strong solution to shape-adaptive energy harvesting and sensing applications for smart electronics at multi-scales. In this work, we aim to enhance the electrospun fiber-based piezoelectric energy harvesting performance by elucidating the role of the solvent in crystallization kinetics and fiber formation during electrospinning as well as its influence on harvesting performance. Two key solvent characteristics, surface tension and evaporation rate, are found to play a role in determining uniform fiber formation with controllable diameters, degree of crystallization, and electroactive β-phase content, which are primarily responsible for the piezoelectric performance of the electrospun poly(vinylidene fluoride-trifluroethylene) P(VDF-TrFE). A substantial difference in the piezoelectric output performance is clearly observed depending on the choice of solvent. Indeed, N,N-dimethylformamide with a low evaporation rate enables piezoelectric output voltage generation of a thermally annealed P(VDF-TrFE) fiber-based device up to 139.5 V, while the device with as-spun fibers in the other solvent case, methyl ethyl ketone, yields a much lower voltage of 75.3 V. This study demonstrates that the tailoring capability of the solvent should be carefully considered together with other processing and operating conditions (e.g., thermal annealing, bending frequency, and electrical resistances) in order to realize enhanced piezoelectric energy harvesting performance of electrospun fibers for versatile potential applications. [ABSTRACT FROM AUTHOR]

(1-x)(Bi0.9La0.1)FeO3–xPb(Fe0.5Nb0.5)O3 (BLFO-PFNO) (x=0.2, 0.7, and 0.8), are investigated as an A-site substituted counterpart multiferroic solid solution of previous (Bi0.9La0.1)FeO3–Ba(Fe0.5Nb0.5)O3 (BLFO-BFNO). The unique BLFO-PFNO solid solution system enables soft ferromagnetism at room temperature and macroscopic polarization with the ferroelectric domain evolution due to nanoscale ordered single grains at high composition of relaxor-type ferroelectric PFNO. [ABSTRACT FROM AUTHOR]

The structure of multi-wall carbon nanotubes has been attributed previously to disordered stacking of the graphene planes. Evidence is presented that the nanotubes analyzed in this paper occur with stacked graphene layers in the sequence of AA′, where alternate graphene planes are translated by half the hexagon width. We further present proof that the crystalline materials comprise graphene helices (∼5 nm in width), rather than in the form of a perfect tube. We also show that the structural model proposed here may be a common structure for multi-wall carbon nanotubes. [ABSTRACT FROM AUTHOR]