Droplet最新文献

Frosting occurs due to the freezing of condensed water droplets on a supercooled surface. The nucleated frost propagates through interdroplet bridges and covers the entire surface, resulting from the deposition of highly supersaturated vapor surrounding tiny droplets. While inhibition of the formation of frost bridges is not possible, the propagation of frost can be delayed by effectively removing tiny droplets. Passive technologies, such as superhydrophobic surfaces (SHS) and hydrophobic slippery liquid-infused porous surfaces (SLIPS), rely on static growth and direct contact with densely distributed droplets. However, use of these approaches in delaying frost propagation involves challenges, as the interdroplet distance remains small. Here, we report a new approach of spontaneous droplet movement on hydrophilic SLIPS to delay the formation of interdroplet frost bridges. Surface tension forces generated by the hydrophilic oil meniscus of a large water droplet efficiently pull neighboring droplets with a diameter of less than 20 μm from all directions. This causes a dynamic separation between water droplets and an adjacent frozen droplet. Such a process delays the formation and propagation of interdroplet frost bridges. Consequently, there is significant delay in frosting on hydrophilic SLIPS compared to those on SHS and hydrophobic SLIPS.

Back Cover: The cover image is based on the Review Article Liquid metal droplet dynamics by Zhao et al.

Gallium-based liquid metal droplets are newly intriguing research targets in diverse areas due to their unique properties which combine the dual merits of both liquids and metals. This review summarizes the latest progress and presents an overview on basic findings related to liquid metal macro-droplet dynamics, including droplet types, fabrication methods, different dynamic behaviors, main challenges, and future perspectives. (DOI: 10.1002/dro2.104)

Front Cover: The cover image is based on the Research Article Digital twin of a droplet microarray platform: Evaporation behavior for multiple droplets on patterned chips for cell culture by Wu et al.

This cover highlights evaporation phenomenon of multiple droplets on patterned surfaces, affected by humidity, temperature, and droplet distribution. We establish a digital twin system and propose a theoretical method to detect volumes and pH variation on evaporating droplets onto patterned substrates. The proposed strategy allows us to achieve an active maneuver of the collective evaporation of droplets on patterned surfaces. (DOI: 10.1002/dro2.94)

Inside Front Cover: The cover image is based on the Research Article Acoustic micro-beam vortex generator for flow actuation inside droplets by Sánchez-Saldaña et al.

A micro-size spiral IDT placed at the base of the droplet leads to an acoustic vortex that induces a poloidal flow inside the droplet with an ascendent flow in the centre and descendent flow in the periphery. This paper shows that the micro-size spiral IDT can control the scale of the flow actuation inside the droplet which in turn can be used for facilitating the operations on particles. (DOI: 10.1002/dro2.96)

Inside Back Cover: The cover image is based on the Review Article Recent advances in droplet-based microfluidics in liquid biopsy for cancer diagnosis by Shi et al.

Droplet-based microfluidics with high throughput, low contamination, high sensitivity, and single-cell/single-molecule/single-exosome analysis capabilities have shown great potential in the field of liquid biopsy. This review aims to summarize the recent development in droplet-based microfluidics in liquid biopsy for cancer diagnosis. (DOI: 10.1002/dro2.92)

Frontispiece: The cover image is based on the Research Article Chemical reaction in a liquid–liquid phase-separated multiple droplet: Synchronization of color change dynamics with droplet movement by Goto et al. (This cover image is licensed under CC BY-NC-ND 4.0.)

Exemplifying self-similarity, a large Matryoshka doll holds a smaller one within. The shape is repeated at different reduced-scales to generate a nested structure. The smallest doll hosts a micro-channel, which formed nested droplets through liquid-liquid phase separation when oil-rich and aqueous alcohol liquids were mixed. (DOI: 10.1002/dro2.93)

Acoustic levitation has developed into a popular but elegant tool for the study of drops as well as soft matter due to its exceptional levitation capabilities to a variety of liquid samples. The acoustically levitated drops offer opportunities for the investigation of a wide range of fundamental issues related to liquid drops. In this review, the unique physics/chemical processes involved in acoustically levitated drops are dealt with. We first introduce the dynamics of the acoustically levitated drops, including drop oscillation, coalescence, and the associated capillary phenomena. The bubble formation and stability are also discussed. Depending on the inhibition of solid surfaces and the nonlinear effects of ultrasound, the self-assembly of colloidal particles at the air–liquid interface as well as granular matter in air is reviewed. In particular, the exploration of biological drops by using acoustic levitation is also highlighted. In the end, the concept of acoustic-levitation-fluidics and possible potential topics are proposed.

The unique properties to combine the dual merits of both liquids and metals together make the gallium-based liquid metal (LM) droplets a class of unconventional substitute which possess great potential for a group of newly emerging areas, such as stretchable electronics, soft devices, micro sensors and actuators. In addition, LM droplets are undoubtedly an intriguing target worth of pursuing in fundamental hydrodynamic investigations due to their extremely high surface tension nature compared to classical nonmetallic fluids. Since the discovery of the diverse transformation phenomena and self-fueled droplet mollusks of LM that can move automatically in solution via single electricity or even without any external energy supply, tremendous attentions were attracted to this special fluidic object of LM droplets. Over the past decade, there has been a proliferation of explorations on LM droplet dynamics, while the involved contents are heterogeneous due to the interfacial physical/chemical activity of the LM and the diversity of the kinetic behaviors. To better understand and manipulate the droplet behavior and to promote further development of the LMs, this review is dedicated to summarize the latest progress and presents an overview on basic findings related to LM macro-droplet dynamics. Firstly, the extended definition of LM droplets and the corresponding fabrication methods are given. Then, typical works on LM droplet dynamics are systematically interpreted based on their different behavior categories. Finally, the perspectives, main obstacles and challenges restricting the development of LM droplet dynamics are pointed out.

Harnessing abundant kinetic water energy in diverse forms of river flows, ocean waves, tidal currents, raindrops, and others, is highly attractive to ease the energy crisis and satisfy the demands of scattered sensor network nodes in the Internet of things. Among them, raindrops, widely and ubiquitously distributed in nature and ambient living life, have been extensively explored and regarded as significant renewable energy carriers. Extensive efforts have been made to investigate droplet-based electricity nanogenerators in fundamental mechanism, performance, and applications for achieving sustainable energy demands of the rapidly developing society over the past decade. In this review, we introduce the remarkable progress in this field and discuss the fundamental mechanisms of droplet energy harvesting technology for achieving high-power generation. More significantly, a systematic review of droplet energy harvesting in different two-phase interfaces, including liquid–solid, liquid–liquid, and liquid–gas interfaces, is provided. Finally, this survey reveals that droplet-based electricity generators present vast potential in the power supply. At the same time, several development challenges and prospective solutions are discussed to spur future technological advancements.

Due to poor chemical robustness, superhydrophobic surfaces become susceptible to failure, especially in a highly oxidative environment. To ensure the long-term efficacy of these surfaces, a more stable and environmentally friendly coating is required to replace the conventional salinization layers. Here, soot-templated surfaces with re-entrant nanostructures are precoated with polydimethylsiloxane (PDMS) brushes. An additional nanometer-thick lubricant layer of PDMS was then applied to increase chemical stability. The surface is superhydrophobic with a nanoscale liquid coating. Since the lubricant layer is thin, ridge formation is suppressed, which leads to low drop sliding friction and fast drop shedding. By introducing a bottom “reservoir” of a free lubricant as an oil source for self-replenishing to the upper layer, the superhydrophobic surface becomes more stable and heals spontaneously in response to alkali erosion and O₂ plasma exposure. This design also leads to a higher icing delay time and faster removal of impacting cooled water drops than for uncoated surfaces, preventing icing at low temperatures.