Droplet最新文献

Droplet impact on solid surfaces is essential both in nature and industry. Precisely regulating the dynamic behavior of droplet impact is of great significance for energy harvesting, anti-icing, inkjet printing, pesticide spraying, and many other fields. Various rebounding behaviors (deposition, rebounding, rotation, instability control, and so on) and rebounding intrinsic parameters (such as contact time) after droplets impacting on solid surfaces can be regulated by surface engineering. This paper reviews the advances in regulating droplet impact behavior from the perspective of symmetry by modifying solid surfaces from the following aspects: chemical modification and physical structure regulation, in which the symmetry is discussed from mirror symmetry and rotational symmetry. Firstly, the symmetry of the droplet impact dynamics and its influencing factors are introduced. Then the modulation of droplet impact symmetry, using homogeneous and heterogeneous chemically modified solid surfaces, is summarized. The following presents the influence of physical structures, from micro to macro scale compared to the droplet size, on the droplet impact symmetry. Finally, the future challenges and opportunities of the droplet impact behavior regulation are discussed.

The high-throughput production of monodisperse droplets is paramount in most of the applications in droplet microfluidics. In a flow-focusing junction, a straightforward way to increase droplet production rate is to increase the flow rates. However, at a critical flow velocity, the droplet monodispersity breaks down due to a transition from the dripping to the jetting regime. As a result, a much more polydisperse droplet population is generated. The change from monodisperse to polydisperse droplet production emerges from the intrinsic properties of the instabilities of jets. In the jetting regime, droplet pinch-off is governed by a convective instability which amplifies random noise when traveling down the jet leading to an irregular breakup. We show that with the use of an amplitude-modulated electric signal, we select the breakup frequency of the jet. Matching the perturbation frequency close to the natural breakup frequency of the jet, we increase the monodispersity of the droplet population. This method is applicable to droplet production at a high throughput, that is, beyond the dripping to jetting threshold, including an active control since the frequency, and hence droplet sizes, are determined by the forcing frequency.

As a typical superwettability behavior, superhydrophobicity can provide an appropriate strategy to enhance the mass transport in multiphase chemical reactions. In the oxidase-based enzymatic reactions, the elaborately regulating of reactant oxygen are critical to the development of an oxidase-based high-performance biosensor. In solid–liquid diphase condition, however, the kinetics of oxidase-catalyzed reactions is inhibited by delayed mass transport and poor solubility of oxygen. To address this limitation, the design of the solid–liquid–air triphase interface is proposed according to the binary cooperation of superhydrophobicity and hydrophilicity. On the triphase joint interface, oxygen required for the oxidase-catalyzed reactions can diffuse directly to the reaction center from the air phase through the micro/nanostructured superhydrophobic substrate, thus improving the kinetics of the oxidase-catalyzed reactions. In this minireview, we summarize recent advances in the fabrication of triphase reaction system based on different superhydrophobic substrate for oxidase-based biosensors. Common substrates including fibrous network, nanowire arrays, 3D porous framework, and hollow sphere structures are outlined in categories.

Control of droplet sliding and its interfacial behavior such as sliding resistance and friction have important applications in microfluidic and energy-related fields. Nature provides many examples of interface-driven droplet sliding control; yet, to date, the continuous governing of the multiphase process and precise steering of droplet sliding remain challenging. Here, directional-dependent ultraslippery patterned surfaces with significant droplet sliding anisotropy were created by coordinating the heterogeneous wettability of the back of the dessert beetle, directional-dependent architecture of the butterfly wing, and ultraslippery configuration of the Nepenthes alata. Analysis of the sliding resistance on typical ultraslippery patterned surfaces reveals that the directional-dependent triple phase line (TPL) immigration on the ultraslippery patterns dominates the strong sliding anisotropy, which can be modeled using the classic Furmidge equation. In particular, the sliding anisotropy for the semicircular ultraslippery patterned surface shows threefold higher than that of natural butterfly wings due to the most significant difference in TPL immigration in two opposite directions, which enables the simultaneous handling of multiple droplets without mass loss and steering of droplet sliding/friction. This work may transform the design space for the control of multiphase interface motion and the development of new lab-on-a-chip and droplet-based microsystems.

Liquid marbles (LMs) are nonsticky droplets stabilized by hydrophobic solid particles that are adsorbed at the liquid–air interface. LMs are emerging as a potential platform in digital microfluidics, sensing applications, storage unit, biological incubation, and cosmetic applications. Incorporating multifunctional particles to form Janus liquid marble (JLM) could enhance the capabilities of the pristine LM. JLMs are multifunctional next-generation LMs comprising two hemispherical domains of distinct physicochemical properties such as size, hydrophobicity, electrical conductivity, surface functionalization, stimuli-responsivity, and so on. The JLMs offer precise control on the manipulability and enhanced performance over pristine LMs. Though the properties, applications, and progress of LMs are detailed in the recent literature, a focused review encompassing the fabrication, recent developments, potential applications of JLMs, and the challenges regarding its reliable fabrication remains a gap in the literature. The review provides insights into the importance of JLMs, systematically discussing the fabrication strategies, applications, challenges, and future directions.

Back Cover: The cover image is based on the Research Article Sustainble dropwise condensation enabled ultraefficient heat pipes by Chang et al.

The combination of hydrophobic condenser with sustained DWC and nano-engineered evaporator in grooved heat pipes can sufficiently decrease both the thermal resistance of condensation and evaporation simultaneously. Up to 82.3% reduction of the total thermal resistance has been realized. An ultrahigh k_eff of ~ 140 kW/(m·K), which is 5.17 times higher than that of traditional groove heat pipes, has been achieved. (DOI: 10.1002/dro2.43)

Inside Back Cover: The cover image is based on the Research Article Slippery quartz surfaces for anti-fouling optical windows by Li et al.

An antifouling transparent window is fabricated on a silica glass surface by infusing lubricant into its porous microstructure prepared by femtosecond laser ablation. The as-prepared surface exhibits great repellence to various liquids, good antifogging ability and stability after immersion into corrosive solutions. Such remarkable characteristics can protect the lens from contamination so as to achieve uninterrupted inspection during endoscopic detection procedure. (DOI: 10.1002/dro2.41)

Inside Front Cover: The cover image is based on the Research Article Preparation of nano-pico droplets using an open fibrous system by Xu et al.

This cover image (DOI: 10.1002/dro2.27) demonstrates that a macroscopic droplet on a micro-/nano-textured copper fiber could be dispersed to a number of tiny droplets by applying and removing a suitable electric potential. The facile strategy offers an innovative open system for continuous preparation of nano-pico droplets.

Front Cover: The cover image is based on the Research Article High performance and wide relative humidity passive evaporative cooling utilizing atmospheric water by Wang et al.

Passive cooling without energy input is highly desirable for solar panels, which improves the solar-to-electricity conversion efficiency and reduces greenhouse gas emissions. This cover image (DOI: 10.1002/dro2.32) demonstrates a passive evaporative cooling technology for solar panels. The cooling technology possesses high cooling performance in a wide range of relative humidity and solar irradiances.

The friction force opposing the onset of motion of a drop on a solid surface is typically considered to be a material property for a fixed drop volume on a given surface. However, here we show that even for a fixed drop volume, the static friction force can be tuned by over 30% by preshaping the drop. The static friction usually exceeds the kinetic friction that the drop experiences when moving in a steady state. Both forces converge when the drop is prestretched in the direction of motion or when the drop shows low contact angle hysteresis. In contrast to static friction, kinetic friction is independent of preshaping the drop, that is, the drop history. Kinetic friction forces reflect the material properties.