Droplet最新文献

Hydrodynamic metamaterials, a nascent research field, possess immense potential for fluid flow manipulation. With engineered structure design, they offer unparalleled control over fluid behavior beyond the capabilities of conventional methods. In this review, we focus on hydrodynamic metamaterials and provide a comprehensive overview of the current state of this research field. We start by introducing basic theories and principles of hydrodynamic metamaterials and then illustrate the different functions of hydrodynamic metamaterials that have been realized in porous medium flow and Hele-Shaw flow. Moreover, we also demonstrate the multifunctional metamaterials that have been developed in hydrodynamics. Some research progresses are highlighted due to their promising applications, including drag reduction, microfluidic manipulation, and biological tissue coculture. The review concludes by identifying major challenges and proposing research directions for the future.

The self-assembly of block copolymers (BCPs) within emulsion droplets is a flexible strategy for the preparation of polymer particles. This strategy permits the fine-tuning of shapes, internal structures, and surface nanostructures of the polymer particles, thus allowing many applications. Although some literature has reviewed the BCP preparation via self-assembly within a droplet, a comprehensive summary including in-depth understanding, controllable preparation, and application is lacked. In this review, we systematically delve into the multiple mechanisms that drive BCP self-assembly within emulsion droplets, such as commensurability effects for minimizing total free energy, interfacial instability, organized spontaneous emulsification, phase separation of multiple components, and entropy effects between BCPs and nanoparticles. Additionally, a strategy combining selective cross-linking and disassembly can further generate Janus particles featuring unique structures. Next, various applications across multiple disciplines are discussed, including drug delivery, display, biomedical imaging, macromolecular separation, and fuel cells. Finally, we present an overview of the current challenges and future directions for BCP emulsion self-assembly, covering mechanism investigation, molecular design, stability control, and application exploration. We anticipate deeper understanding, more varieties, enhanced performance, and broader applications can be achieved with BCP emulsion self-assembly after addressing the challenge.

During the solidification of a sessile drop, the effect of heat exchange from the gaseous environmental medium is generally ignored. However, by combining experimental observations, direct numerical simulations, and a theoretical model, we have demonstrated that the environmental medium, particularly one with high thermal conductivity such as a liquid, has nonnegligible heat exchange with both the drop and the substrate, leading to accelerated cooling of the outer surface of the sessile drop. Consequently, it causes alterations in the geometry of the freezing front and ultimately results in the formation of a solidified shell that encloses the drop. Furthermore, the encapsulated liquid continues to solidify, which induces volume change and consequently changes the final outcome of the freezing process. This study highlights the importance of considering the properties of the environmental medium and provides novel strategies to manipulate the freezing rate and reshape the morphology of the solidified drop.

Water is one of the most essential substances for life on Earth and plays a vital role in both natural and technological processes. Recently, there has been growing interest in studying the behavior of water molecules in confined spaces, particularly in low-dimensional materials and structures. Regardless of whether it is in the form of gas, liquid, or solid, water can interact and form interfaces with many low-dimensional structures. Given the current controversial understanding of two-dimensional (2D) ice and the increasing interplay between water/ice and 2D materials such as graphene and transition-metal dichalcogenides, we provide a brief overview of recent progresses on the interfaces of 2D ice and 2D van der Waals layered materials. This review highlights their potential contributions to the breakthroughs in tribology, membrane technology, nanofluidic, and nanodevice applications. Of particular interest is the recent discovery of ultrahigh lubricity between 2D ice and 2D layered materials, as well as the ability to modulate the surface adhesion between layers. These findings have the potential to enable new technological advances in both electronics and various industries. Meanwhile, this rapidly evolving field presents its own challenges, and we also discuss future directions for exploiting the interactions between 2D ice and 2D layered materials.

Reducing the contact time during droplet impact is essential for many scientific and industrial applications, such as self-cleaning, anti-icing, heat transfer, and condensation. This paper reports contact-time reduction by coating droplets with micro–nano hydrophobic particles. Such particle-coated droplets are known as liquid marbles (LM). LM impact on superhydrophobic surfaces reveals two different modes of contact-time reduction. For lower impact energies, the reduced adhesion of LM with the surface is responsible for a reduction of up to 21%. Contact-time reduction in this regime is found to be independent of particle size but dependent on the solid fraction of LM. However, a fragmentation-based contact-time reduction is observed for larger particle sizes and higher impact energies. Here, the reduction is as high as 65%. Such fragmentation occurs because the spreading LM lamella breaks when its thickness becomes similar to particle dimensions. Our findings reveal the potential of LM as a novel approach to reduce contact time during droplet impact, with implications for various scientific and industrial applications.

Switchable hydrophilicity solvents (SHSs) are a unique class of chemical compounds that can be switched between their hydrophobic and hydrophilic forms. The switchable characteristics allow SHSs to be used as emerging, green solvents for sustainable extraction and separation technology. In the production of polymeric microparticles from recycled plastics, SHSs are used to dissolve the polymer and then are switched to the hydrophilic form for separation from the generated polymeric microparticles. However, it is extremely difficult to fully recover the SHS residue from the mixtures. In this work, we will identify the key parameters that determine the level of the solvent residue during the switched-on dissolution of emulsion microdroplets. The SHS N,N-dimethylcyclohexylamine from solvent–polymer binary emulsion droplets was switched to the hydrophilic, water-soluble form, triggered by addition of an acid in the surrounding aqueous phase. By applying a sensitive detection method developed in this work, we compared the levels of SHS residue in polymer microparticles obtained under 30 different dynamical and chemical conditions for the switching processes. The quantitative analysis revealed that residue levels remained constant at varied addition rates and concentration of the trigger solution, but decreased with the increase in organic phase fractions or the decrease in the emulsion temperature. Trapped water in the drops during switched-on dissolution may have contributed to the high level of solvent residue. The understanding of the new possible mechanism for residual solvent reported in this work may help develop effective approaches for the recovery of switchable solvents in environmentally friendly separation processes.

Evaporation of droplets composed of insoluble materials provides a low-cost and facile route for assembling materials and structures in a wide spectrum of functionalities down to the nanoscale and also serves as a basis for innovating ink-solution-based future manufacturing technologies. This review summarizes the fundamental mechanics theories of material assembly by droplet drying both on solid and liquid substrates and in a fully suspended air environment. The evolution of assembly patterns, material deformation, and liquid flow during droplet drying and its response to external stimuli ranging from solution surfactant and pH value, surface geometric pattern and wettability, drying temperature, pressure environment, to electrical field have been highlighted to elucidate the coupling mechanisms between solid materials and liquid solutions and the manipulation strategies for material assembly through an either active or passive means. The recent progresses in ink-based printing technologies with selected examples are also presented to illustrate the immediate applications of droplet drying, with a focus on printing electronic sensors and biomedical devices. The remaining challenges and emerging opportunities are discussed.

Capillary-enabled water energy harvesters (WEHs) are capable of generating direct-current electricity continuously. However, active-metal electrodes can introduce metal–air batteries in these WEHs. Given the nearly identical device structures and output characteristics of these two technologies, it is essential to distinguish between them. Herein, we present a systematic study of the water-activated metal–air battery (WMB) through theoretical analyses and experimental verifications. We conclude the general formation rules of the WMB from a material and device-structure perspective. Furthermore, we provide a comparative summary of various WEHs and WMBs for easy identification. We aim to improve the comprehension of metal–air batteries in the field of WEHs and assist in distinguishing between these technologies.

Water, the source of life, contains immense energy and manifests in diverse forms. Hydrovoltaic technology enables the direct interaction between water and materials to generate electricity, a vital necessity for industry modernization. Due to the ubiquitous presence and easy availability of falling water, hydrovoltaic energy derived from water droplets has attracted considerable attention and shown great potential in raindrop energy harvesting. In this review, a comprehensive summary of the latest advancements in harvesting hydrovoltaic energy from water droplets is presented, with a focus on the configurations and underlying mechanisms of hydrovoltaic devices. Additionally, a brief discussion on the applications of droplet-based hydrovoltaic devices is presented, along with future prospects for this energy-harvesting technology.

Fog Harps harvest substantially more water than conventional mesh-based harvesters. However, to date, all large-scale Fog Harps have been impractically hand-wound at low wire tensions and suffer from elastocapillary wire tangling. Here, we develop large-scale and high-tension Fog Harps that are manufacturable and antitangling. These Fog Harps retain the record-setting fog harvesting efficiency ($��\eta �\approx �17�$%) of their optimized scale-model counterparts, while uniquely enabling practical real-life implementation. Manufacturability was achieved by adapting the industrial process for making harp screens, a pre-existing technology used for screening solid materials. The critical tension required to minimize wire tangling was rationalized by an improved elastocapillary tangling model.