A many-body dissipative particle dynamics with energy conservation study of droplets icing on microstructure surfaces

Droplets icing has important applications in real life. The icing process of droplets on microstructure is explored based on the MDPDE method in this study. Firstly, the correctness of the heat transfer model was verified by one-dimensional heat conduction simulation, and then the feasibility of the phase change model was verified by investigating the icing process of droplets. The influence of cold surface temperature, droplet volume and contact angle on freezing time of droplets was discussed, and it was found that the temperature of cold surfaces had a greater effect on freezing. We finally explored the influence of different microstructure surfaces on the icing of droplets, and results showed that the presence of microstructures greatly enhanced the anti-icing effect of the surface. In our research, the contact angle is a relatively large factor affecting the icing of droplets. In addition, it was discovered that the droplet had the strongest ability to delay freezing on the surface of triangle microstructures with a contact angle of 157.1°.

Independent Control Over Size and Surface Density of Droplet Epitaxial Nanostructures Using Ultra-Low Arsenic Fluxes

Modern and future nanoelectronic and nanophotonic applications require precise control of the size, shape and density of III-V quantum dots in order to predefine the characteristics of devices based on them. In this paper, we propose a new approach to control the size of nanostructures formed by droplet epitaxy. We reveal that it is possible to reduce the droplet volume independently of the growth temperature and deposition amount by exposing droplets to ultra-low group-V flux. We carry out a thorough study of the effect of arsenic pressure on the droplet characteristics and demonstrate that indium droplets with a large initial size (>100 nm) and a low surface density (<108 cm−2) are able to shrink to dimensions appropriate for quantum dot applications. Small droplets are found to be unstable and difficult to control, while larger droplets are more resistive to arsenic flux and can be reduced to stable, small-sized nanostructures (~30 nm). We demonstrate the growth conditions under which droplets transform into dots, ring and holes and describe a mechanism of this transformation depending on the ultra-low arsenic flux. Thus, we observe phenomena which significantly expand the capabilities of droplet epitaxy.

Dynamic Reversible Evolution of Wrinkles on Floating Polymer Films under Magnetic Control

In this paper, we present a simple and versatile method to dynamically and reversibly tailor surface wrinkles on a floating polymer film by combining a magnetic droplet and neodymium magnet. The magnetic force from the attraction of the neodymium magnet to the magnetic droplet is the main reason for surface instabilities of floating polymer films, which can induce radial stress in the radial direction, and further, compressive stress in the circumferential direction. This compressive stress can trigger not only floating film wrinkling but also a wrinkle-fold transition. Surface morphologies on the floating polymer film have been systematically studied, by varying the distance between the magnetic droplet and neodymium magnet, polymer film thickness, and magnetic droplet volume. With the decrease in the distance between a magnetic droplet and a neodymium magnet, the decrease in polymer film thickness, and the increase in the magnetic droplet volume, the wrinkle numbers increase and even a wrinkle-fold transition happens. Additionally, the coupling effect of multiple magnetic droplets on the floating film has also been used to achieve novel surface wrinkle patterns, which greatly widens the applications of surface wrinkling.

Insecticide spray drift reduction with different adjuvants and spray nozzles

ABSTRACT Insecticide spray drift can lead to reduced control efficiency and loss of product to the environment. Thus, we conducted a study to evaluate the effect of different spray nozzles and the addition of adjuvants in insecticide spray on the resulting droplet spectrum and wind tunnel drift. All experiments were conducted in a completely randomized design with four repetitions using a 5 × 3 factorial scheme. Five spraying solutions were studied; one contained only water and the other four comprised thiamethoxam + lambda-cyhalothrin (no adjuvant, Oro-solve, Wetcit Gold, and Orobor N1), in combination with three spray nozzles (AXI, JFC, and J3D). The droplet spectrum was evaluated through the volumetric median diameter, relative amplitude, and percentage of the droplet volume with diameter ≤ 100 µm. The drifts were evaluated in a wind tunnel at 5, 10, and 15 m. Data were subjected to analysis of variance and means were compared using the Tukey’s test. In addition, a principal component analysis was performed. Application of the insecticide with the adjuvants combined with the different nozzles changed the droplet spectrum and the risk of drift. The AXI nozzle and the J3D associated with the Oro-solve and Wetcit Gold adjuvants resulted in a greater volumetric median diameter of the droplets and drifts were observed at 5 m.

Novel electrodes for precise and accurate droplet dispensing and splitting in digital microfluidics

Digital microfluidics (DMF) is a versatile fluid handling tool that is widely used in the biochemical field. There are very high requirements for the volume of single droplet in many biochemical applications. Droplet dispensing and splitting are two main operations to generate a single droplet in DMF. Therefore, the generation of droplets with high volume precision and accuracy in the two droplet operations is one of the keys to the efficient application of DMF in biochemical analysis. We have developed a novel droplet dispensing and splitting scheme where electrode geometry is optimized. The liquid column can contract in a regular shape, which keep the neck shape uniform and stable, and the position of pinch-off point was fixed; meanwhile, the liquid tail is eliminated before pinching off, so that the precision and accuracy of droplet volume were greatly improved. The increase in the radius of the cutting electrodes elongated the droplet neck and increased the neck curvature at the pinch-off point, which further effectively improved the precision and accuracy of droplet volume. The optimized droplet splitting scheme can also be applied to the droplet splitting with unequal volume effectively.

Switchable Electrohydrodynamic Capillary Bridges

<p>The deformation of sessile droplets and capillary bridging in a parallel-plate capacitor under DC fields has been the subject of several scientific studies. Coaxially located droplets on opposing electrodes experience an attraction in the presence of an electric field. Application of a suitably large field will lead to either the droplets forming a liquid bridge or oscillation between bridged and de-bridged (i.e. droplet) states. We explored the bridging behavior of a variety of liquids in air. Among the liquids and droplet geometries that could form a stable field-induced bridge, only a limited set could reversibly make and break the capillary bridge by switching the electric field on and off. The ability to form a switchable liquid bridge is a function of both the liquid’s properties, including surface tension, electric conductivity, and dielectric constant, and external conditions such as electrode separation, droplet volume.</p>

Switchable Electrohydrodynamic Capillary Bridges

<p>The deformation of sessile droplets and capillary bridging in a parallel-plate capacitor under DC fields has been the subject of several scientific studies. Coaxially located droplets on opposing electrodes experience an attraction in the presence of an electric field. Application of a suitably large field will lead to either the droplets forming a liquid bridge or oscillation between bridged and de-bridged (i.e. droplet) states. We explored the bridging behavior of a variety of liquids in air. Among the liquids and droplet geometries that could form a stable field-induced bridge, only a limited set could reversibly make and break the capillary bridge by switching the electric field on and off. The ability to form a switchable liquid bridge is a function of both the liquid’s properties, including surface tension, electric conductivity, and dielectric constant, and external conditions such as electrode separation, droplet volume.</p>