Droplet最新文献

An important feature of contact line motion, as an irreversible process, is its dissipative nature, which can dominate the dynamics during the early stages of droplet spreading. A phenomenological contact line friction coefficient $�{\mu }_f$, obtained through direct matching of phase-field simulations and experimental observations, emerges as an effective parameter for quantifying this dissipation. This paper provides a comprehensive overview of $�{\mu }_f$, its experimental determination, and its relevance across a variety of surfaces and conditions. We discuss when and why $�{\mu }_f$ becomes the dominant source of dissipation, and examine how it is modulated by factors such as liquid viscosity, surface chemistry, substrate topography, and external stimuli including electric potential. This review highlights the importance of $�{\mu }_f$ in bridging molecular-scale processes and macroscopic wetting dynamics, reflecting the intrinsic material response of the three-phase system.

Frost and ice are ubiquitous in nature and industry, and sometimes cause problems. The solidification of water droplets is in the early stage of frosting and icing and has attracted extensive research interest. However, due to physical occlusion, solidification characteristics inside a droplet are always unclear. In this study, Hele‒Shaw cells were used to produce cross-sectional slices of water droplets deposited on hydrophilic and hydrophobic surfaces, referred to as two-dimensional droplets. The solidification characteristics of these droplets were investigated at micrometer spatial and millisecond temporal scales. Results show that the maximum dendrite growth velocity reached 0.45 m/s during the recalescence stage. Using the side‑view freezing front height from a three‑dimensional droplet as a proxy for the true front height introduces errors ranging from ‒35% to +45%. For a ‒30°C substrate, the maximum longitudinal temperature difference within the droplet reached 7.3°C. Additionally, micro-scale trapped air bubbles with equivalent diameters ranging from 18 to 78 µm switch their growth mode from spheroidal to longitudinal approximately 250 ms into the freezing stage, corresponding to about 17% of the total growing time. These findings provide new insight into frosting and icing physics and may inform enhanced defrosting and de‑icing strategies.

This study investigates how pathogen-laden respiratory droplets transfer diseases via inanimate surfaces. Respiratory fluid ejections containing pathogens pose a significant health threat, especially in high-traffic areas such as hospitals, public transport, restaurants, and schools. When these droplets dry on surfaces, they form deposits that can transfer pathogens to healthy individuals through contact and can be ingested via the oral or nasal route. The study examined the effects of varying salt and mucin concentrations in respiratory fluid droplets containing Pseudomonas aeruginosa. Results showed that P. aeruginosa viability increased 10-fold at elevated mucin concentrations, while changes in salt concentration had minimal impact. Adhesive properties of the deposits were analyzed using atomic force spectroscopy and scotch tape test. Pathogen transfer from the deposit to a fingerprint patterned model thumb at different relative humidity (RH) levels was assessed using confocal microscopy, showing significant pathogen transfer at elevated RH. Out of 10⁶ CFU/mL pathogens in deposits, 17%‒38% are potentially transferable, with most of the transfer occurring from the droplet's edge deposits. The study demonstrated that the combined variation in salt and mucin concentrations significantly influences the evaporation, flow, and precipitation dynamics of droplets. These changes, in turn, affect the solutal deposition and distribution of pathogens within the droplet, ultimately altering the survivability and transmissibility of the pathogen.

The growing demand for surface-enhanced Raman scattering sensors in biochemical detection, environmental monitoring, microfluidics, and other fields has promoted the development of highly sensitive and stable substrates. Femtosecond laser-fabricated surfaces with controlled wettability, unique micro/nanostructure designs, and tunable extreme wetting properties can significantly enhance the signal amplification and reproducibility of surface-enhanced Raman scattering techniques. In this review, we offer a comprehensive overview of recent advancements in surface-enhanced Raman scattering techniques based on superwetting surfaces fabricated by femtosecond laser processing, including fully superhydrophobic surfaces, hybrid wettability surfaces, and visual localization surfaces. The main research areas, such as pattern optimization, dynamic measurements, hot spot enhancement, and stability improvement, are highlighted. We also summarize the practical applications of surface-enhanced Raman scattering in chemical detection, microfluidic control, medical diagnosis, and food safety evaluation. Finally, the current challenges and limitations in the development of femtosecond laser-processed superwetting substrates for surface-enhanced Raman scattering are described.

Rapid and accurate detection of ultralow-concentration nanoparticles is crucial for applications ranging from medical diagnosis to water quality monitoring, yet remains challenging for current laser-based and light-scattering methods. While nanoparticle-translocation-based nanopore sensing offers single-particle resolution, conventional single-nanopore resistive pulse sensing approaches suffer from low capture frequency, transient signals, and clogging issues, limiting their effectiveness at extremely low concentrations. Here, we present a novel nanopore array blockage-based sensing strategy for the rapid detection and quantification of ultralow-concentration nanoparticles. Using hydraulic force, nanoparticles are driven through an array of subnanoparticle-sized pores, and optical microscopy monitors blockage progression to obtain quantitative concentration data. Our results demonstrate a linear correlation between the initial blockage rate and nanoparticle concentration, enabling the detection of fluorescent nanoparticles down to 0.5 aM (300 particles/mL) within 5 min—a three-order-of-magnitude improvement in sensitivity over previous nanopore-based methods. Additionally, our approach can leverage fluorescent nanoparticles as probes to detect unlabeled nanoparticles and contaminants at similarly low concentrations. This strategy provides a robust, efficient, and rapid platform for ultrasensitive nanoparticle detection, with promising applications in biomedical research, environmental monitoring, and industrial quality control.

In this work, we experimentally measured the pinch-off of a gas bubble on a biphilic surface, which consisted of an inner circular superhydrophobic region and an outer hydrophilic region. The superhydrophobic region had a radius of R_SH varying from 2.8 to 19.0 mm, where the large R_SH modeled an infinitely large superhydrophobic surface. We found that during the pinch-off, the contact line had two different behaviors: for small R_SH, the contact line was fixed at the boundary of superhydrophobic and hydrophilic regions, and the contact angle gradually increased; in contrast, for large R_SH, the contact angle was fixed, and the contact line shrank toward the bubble center. Furthermore, we found that regardless of bubble size and contact line behavior, the minimum neck radius collapsed onto a single curve after proper normalizations and followed a power–law relation where the exponent was close to that for bubble pinch-off from a nozzle. The local surface shapes near the neck were self-similar. Our results suggest that the surface wettability has a negligible impact on the dynamics of pinch-off, which is primarily driven by liquid inertia. Our findings improve the fundamental understanding of bubble pinch-off on complex surfaces.

Harvesting electricity from ubiquitous moisture offers the promise of clean power for self-sustained systems. Despite extensive efforts, achieving high-power electricity generation remains challenging. Existing studies mimicking electric eels’ electrogenesis to enhance their electrical performance focused on the two-membrane structure that linearly adds up the voltage, but their current output was either transient or limited to microamperes, because of the large resistance for ion diffusing across material interfaces. Here, we report an electrocyte-inspired moisture-driven electricity generator (EMEG) made from an interphase-mediated Janus film. The continuous interphase significantly alleviates the ion migration resistance, boosting the current output to 150 µA and sustaining the voltage of 0.8 V continuously for more than 1000 h. We also show that integrated EMEGs were easily assembled to self-powered smart watch for emergency rescue. Furthermore, the integrated EMEGs achieved self-sustained and moisture-powered water splitting with a steady hydrogen production. Our results provide a rational for bio-inspired designs toward green and sustained power generation.

The development of biomimetic chloroplasts offers significant potential in addressing global energy and environmental challenges. Traditional droplet-based models are limited by transmembrane transport inefficiencies, leading to the accumulation of aqueous products that severely hinder reaction performance. In this work, we present a biomimetic chloroplast system that integrates light-dependent and light-independent reactions, reaction compartments, and selectively permeable interfaces, fabricated using a biphasic microfluidic platform. The permeable interface facilitates continuous substrate–product exchange, mitigating product inhibition and side reactions, thus enhancing reaction efficiency. Furthermore, a quartz spiral tube was engineered to amplify Dean vortex effects, improving mass transfer. This system exhibited a nicotinamide adenine dinucleotide regeneration efficiency during light-dependent reactions that was 5.52 times higher than that of conventional slurry reactors. In the light-independent reaction, the energy conversion efficiency for the transformation of α-ketoglutaric acid to L-glutamic acid reached 1.45 times that of natural photosynthesis. As the first comprehensive integration of photosynthetic processes within artificial chloroplasts, this work combines biological mechanisms with engineered components to establish a transformative platform for efficient energy conversion and directional biosynthesis. This breakthrough advances the field of photocatalysis and bioinspired technologies, with wide-reaching implications for sustainable energy and synthetic biology applications.

Back Cover: The cover image is based on the Research Article Hypergolic droplet–film interaction dynamics at high temperatures by Song et al.

Cover description: This cover image illustrates the phenomenon of chemically induced micro-explosions generated when an oxidizer droplet impacts a liquid fuel film, accompanied by the formation of numerous high-temperature micro-droplets. Our research clarifies the reactive processes occurring between the coolant films on the thrust chamber walls of liquid rocket engines and the settling oxidizer droplets from the mainstream region, and how these reactions affect the cooling efficiency of the liquid film. (DOI: 10.1002/dro2.70003)

Inside Back Cover: The cover image is based on the Research Article Bubble-induced symmetry breaking in droplet impact by Zhou et al.

Cover description: On flat surfaces, impacting droplets typically exhibit symmetric bouncing dynamics. Here, we demonstrate that embedding a pair of bubbles within a droplet enables asymmetric impact behavior on super-repellent surfaces, where spreading and receding occur simultaneously. This symmetry-breaking dynamics reduces both contact time and contact area, arising from anisotropic capillary effects induced by the encapsulated bubbles. (DOI: 10.1002/dro2.70006)