Droplet最新文献

This paper demonstrates the use of deep learning, specifically the U-Net model, to recognize the menisci of droplets in an electrowetting-on-dielectric (EWOD) digital microfluidic (DMF) device. Accurate recognition of droplet menisci would enable precise control over the movement of droplets to improve the performance and reliability of an EWOD DMF system. Furthermore, important information such as fluid properties, droplet characteristics, spatial position, dynamic behavior, and reaction kinetics of droplets during DMF manipulation can be understood by recognizing the menisci. Through a convolutional neural network utilizing the U-Net architecture, precise identification of droplet menisci is achieved. A diverse dataset is prepared and used to train and test the model. As a showcase, details of training and the optimization of hyperparameters are described. Experimental validation demonstrated that the trained model achieves a 98% accuracy rate and a 0.92 Dice score, which confirms the model's high performance. After the successful recognition of droplet menisci, post-processing techniques are applied to extract essential information such as the droplet and bubble size and volume. This study shows that the trained U-Net model is capable of discerning droplet menisci even in the presence of background image interference and low-quality images. The model can detect not only simple droplets, but also compound droplets of two immiscible liquids, droplets containing gas bubbles, and multiple droplets of varying sizes. Finally, the model is shown to detect satellite droplets as small as 2% of the size of the primary droplet, which are byproducts of droplet splitting.

Ladybirds (Coccinella septempunctata) are adept at living in humid conditions as their elytra can effectively shield their bodies from raindrops. However, due to technical difficulties in examining the delicate structure, the understanding of the water-proofing mechanism of the coupling structure and its impact on the dome-like elytra response to the raindrops remain elusive. In this combined experimental and theoretical study, we showed that the coupling structure on the ladybird elytra can ward off the raindrops traveling at a velocity of 6 m/s, which generates an impact force equivalent to 600 times the body weight. The waterproofing mechanism relies on the deformability of the elytra and their microstructures, which collectively impedes the formation of microchannels for liquids. The enhanced water-proofing capabilities enabled by the coupling structures are validated through experimental testing on comparative 3D-printed models, showing the effectiveness of these structures in improving water resistance. Subsequently, we showcased a water-proofing device, which substantially improved the efficiency of solar panels in converting solar energy. This multidisciplinary study not only advances our understanding of the biomechanics of coupling systems in insects but also inspires the design of water-proofing deployable structures.

Given recent interest in laboratory automation and miniaturization, the microdroplet research space has expanded across research disciplines and sectors. In turn, the microdroplet field is continually evolving and seeking new methods to generate microdroplets, especially in ways that can be integrated into diverse (microfluidic) workflows. Herein, we present a convenient, low-cost, and re-usable microdroplet generation device, termed as the “NanoWand,” which enables microdroplet formation in the nanoliter volume range through modulated surface energy and roughness, that is, an open surface energy trap (oSET), using commercially available and readily assembled coating and substrate materials. A wand-like shape is excised from a microscope glass cover slip via laser-micromachining and rendered hydrophobic; a circle is then cut-out from the hydrophobically modified wand's tip using laser-micromachining to create the oSET. By adjusting the size of the oSET with laser-micromachining, the volume of the microdroplet can be similarly controlled. Using liquid microjunction–surface sampling probe–mass spectrometry (LMJ-SSP-MS), specific NanoWand droplet capture volumes were estimated to be 117 ± 23.6 nL, 198 ± 30.3 nL, and 277 ± 37.1 nL, corresponding to oSET diameters of 0.75, 1.00, and 1.25 mm, respectively. This simple approach provides a user-friendly way to form and transfer microdroplets that could be integrated into different liquid handling applications, especially when combined with the LMJ-SSP and ambient ionization MS as a powerful and rapid analytical tool.

Evaporation of saline droplets significantly impacts industrial processes such as water and gas treatment. Simulations, with advantages in describing temperature, concentration, and velocity distribution inside the droplet, receive increasing attentions. This paper summarized research on numerical simulations of droplet evaporation at micro-, meso-, and macroscales, emphasizing saline or multicomponent droplets. Accurate description of physics at phase interfaces and within proves to be critical for modeling. While recent studies have investigated on interface motion and temperature distribution, the coupling effect of internal concentration and flow distribution is still rarely considered. Among numerical methods, the lattice Boltzmann method is suitable for droplet scale due to its ability to handle non-continuum behavior. Bridging multiscale models remains a challenge, particularly in describing Marangoni and capillary flows. Experimental approaches to the effects of external physical fields (electric, magnetic, convection, and laser) and substrate properties on evaporation were also reviewed. Visualizing evaporation under various conditions can validate macroscopic models, while experiments with different substrates can validate molecular scale simulations, as substrate properties primarily affect evaporation by affecting capillary flow at the droplet bottom. This paper comprehensively reviewed numerical research on droplet evaporation, and analyzed the advantages, limitations, and development directions of various numerical methods.

Evaporation deposition of a spilt sugary drop on the supporting surface can attract ants to surround it. People have a long history of using this phenomenon as an implication of sugar in the drop. Unfortunately, it is hard to detect sugar concentration and has to depend exclusively on ants. Here, we show a facile strategy for the eye-naked detection on sugar concentrations in common liquid mixtures, based on their evaporation depositions. Our experiments show that evaporation drops without any sugar form clear ring-like depositions, and the width of the ring area enlarges with the increase in sugar concentration. We demonstrate that the increase in sugar concentration can increase the liquid viscosity and decrease the capillary flow velocity, thus weakening the “coffee ring” effect. Our further experiments indicate that the temperature has insignificant effects on the correlation between sugar concentrations and ring-like depositions, but the substrate wettability impacts on the correlation by promoting the formation of ring-like depositions. Based on the mechanism study, we develop a strategy for detecting sugar concentrations via quantitatively correlating them with the width of the ring area, and demonstrate that it is valid for various liquid mixtures, for example, carbonate beverage, liquid medicine, and plant nutrient. Our findings not only present new insights into the understanding of the sugary drop evaporation, but also provide a facile strategy of detecting sugar concentration that promises great applications in food safety, pharmaceutical detection, and agricultural product measurements.

Many regions across the globe are grappling with water scarcity issues, prompting the exploration of innovative water harvesting techniques. While the development of high-performance water harvesting materials has been widely documented, these technologies often rely on a singular source with limited efficiency. This study presents a dual-functional copper Janus system that facilitates continuous freshwater harvesting by integrating seawater desalination powered by solar energy during daylight hours and fog collection during night and morning time. The Janus system consists of a copper sheet and copper foam substrate, featuring superhydrophilic pores arranged on the superhydrophobic surface, as well as superhydrophilic flake-like structures made of soot-carbon particles, which are deposited on the framework of the copper foam. The fog collection rate of this system has been measured at 210.65 kg m⁻² h⁻¹, while the solar-driven evaporation rate of seawater under 1-sun conditions is reported at 1.44 kg m⁻² h⁻¹. The fog collection and evaporation efficiency have been enhanced by 28.72% and 183.27%, respectively. Furthermore, the system demonstrates strong and consistent performance even after repeated use, ensuring sustained water collection over prolonged periods. Therefore, this study presents a promising avenue for water collection technologies and offers valuable insights for the advancement of sustainable freshwater production methods.

Front Cover: The cover image is based on the Research Article DropletMask: Leveraging visual data for droplet impact analysis by Zhao et al.

Cover description: Capturing the dynamic movements of droplet impacts is critical in thermal science and applications involving droplets. We propose a framework that leverages machine learning-assisted computer vision tools that quantitatively analyze their impacts. The interconnected network on the image background represents digital droplets, enabling precise measurements of the spatiotemporal data involving droplet movements, sizes, and impact forces on various surfaces. (DOI: 10.1002/dro2.137)

Inside Back Cover: The cover image is based on the Research Article Electro-coalescence of heterogeneous paired-droplets under AC electric field by Tao et al.

Cover description: Electro-coalescence of heterogeneous paired-droplets is achieved within milliseconds under AC electric fields on a lab-on-a-chip platform. The physical mechanisms are examined by parameters such as conductivity, surface tension, non-Newtonian properties. This technique could be applied to the droplet-based chemical reaction at microscale, including the efficient and additive-free fabrication of hydrogel microspheres. (DOI: 10.1002/dro2.145)

Inside Front Cover: The cover image is based on the Research Article A facile method to fabricate cell-laden hydrogel microparticles of tunable sizes using thermal inkjet bioprinting by Suntornnond et al.

Cover description: We demonstrate a novel approach for fabricating hydrogel microparticles (HMPs) using thermal inkjet-based bioprinting. The technique enables precise control over HMP size, porosity, and modularity, with potential applications in tissue engineering and regenerative medicine. Cell-laden HMPs of tunable sizes can be fabricated by adjusting surfactant concentration and jetting volume, highlighting their versatility for advanced biomedical applications. (DOI: 10.1002/dro2.144)

Back Cover: The cover image is based on the Research Article Programmable curvilinear self-propelling of droplets without preset channels by Feng et al.

Cover description: We propose a programmable curvilinear self-propelling strategy for droplets based on the collaboration of curvilinear wetting gradient and the Leidenfrost effect. This design achieves a well-controlled manner in motion trajectory, as well as high velocity and long distance of droplet transport independent on the pre-set channel. (DOI: 10.1002/dro2.138)