Droplet最新文献

Inside Back Cover: The cover image is based on the Research Article Collective wetting transitions of submerged gas-entrapping microtextured surfaces by Arunachalam and Mishra.

A variety of scenarios entail undesirable or accidental immersion in water, e.g., “smart” gadgets or air-breathing marine/land insects. We found that the air-filled microcavities can “communicate” with each other via diffusion and, thus, exhibit directionality as they get filled. The fascinating science behind this collective, directional wetting transitions is unveiled, which should inspire technologies for protecting devices against water ingression. (DOI: 10.1002/dro2.135)

Front Cover: The cover image is based on the Research Article Heat transfer during droplet impact on a cold superhydrophobic surface via interfacial thermal mapping by Kumar et al.

Superhydrophobic surfaces reduce the contact area and duration of an impacting droplet, which limits the heat transfer at the solid-liquid interface. This makes superhydrophobic surfaces promising for anti-icing applications. Our work employs spatio-temporally resolved infrared thermography to investigate the effects of contact area and time on interfacial heat transfer as a droplet impacts the cold superhydrophobic surface. (DOI: 10.1002/dro2.124)

Inside Front Cover: The cover image is based on the Research Article Quantitative liquid storage by billiards-like droplet collision on surfaces with patterned wettability by Li et al.

The mass transfer of droplets involves collision and separation, similar to the motion transfer in billiard ball impacts. This droplet transport occurs spontaneously, without the need for external energy fields or gravitational forces, as demonstrated by the level surface of a billiard table. The table's pockets symbolize the quantitative storage of droplets. (DOI: 10.1002/dro2.125)

Back Cover: The cover image is based on the Research Article A strategy to drive nanoflow using Laplace pressure and the end effect by Zhang et al.

When two droplets of unequal sizes connected by a tube, the radius of the larger droplet gradually increases, while the smaller droplet becomes progressively smaller. Finally, the smaller droplet vanishes as if it was inhaled by the larger one. Based on this finding, we theoretically demonstrated a strategy to drive nanoflow using the Laplace pressure. (DOI: 10.1002/dro2.136)

Nanofluidics holds significant potential across diverse fields, including energy, environment, and biotechnology. Nevertheless, the fundamental driving mechanisms on the nanoscale remain elusive, underscoring the crucial importance of exploring nanoscale driving techniques. This study introduces a Laplace pressure-driven flow method that is accurately controlled and does not interfere with interfacial dynamics. Here, we first confirmed the applicability of the Young–Laplace equation for droplet radii ranging from 1 to 10 nm. Following that, a steady-state liquid flow within the carbon nanotube was attained in molecular dynamics simulations. This flow was driven by the Laplace pressure difference across the nanochannel, which originated from two liquid droplets of unequal sizes positioned at the channel ends, respectively. Furthermore, we employ the Sampson formula to rectify the end effect, ultimately deriving a theoretical model to quantify the flow rate, which satisfactorily describes the molecular dynamics simulation results. This research enhances our understanding on the driving mechanisms of nanoflows, providing valuable insights for further exploration in fluid dynamics on the nanoscale.

Unwanted ice formations may cause severe functional degradations of facilities and also have a negative impact on their lifespans. Avoiding and removing ice accumulation is always a hot topic in the industrial and technological field. Bionic functional surfaces have been greatly studied for several decades and have proved to be excellent candidates for passive anti-/deicing applications. However, the drawbacks limit their potential industrial uses under harsh conditions, like low temperatures and high humidity. Most researches on bionic surfaces are focused on a certain function of natural creatures and their underlined fundamental theories are revealed by taking the interface as the static. Actually, living organisms, either plants or animals, are often sensitive and responsive to their surroundings, avoiding risks and even self-repairing upon damage. From this prospect, a novel view of the bionic icephobic materials has been proposed in the present review, which is expected to be studied and designed by taking the biological species as a system. As two representative icephobic materials, the anti-/deicing theories of superhydrophobic and slippery surfaces are first discussed. Further, the recent progress of smart icephobic strategies is summarized from interfaces to substrates. We aim to provide new bionic insights on designing future icephobic strategies.

Water droplets help life in nature survive, thrive, and evolve. With water droplet serving as one of the indispensable elements in the Internet of Things (IoT), many droplet-oriented technologies, such as microfluidics, droplet manipulation, electrowetting, and energy harvesting, make rapid progress driven by material science, computer science, and medicine. Droplet-based wearable devices are endowed with advantages such as flexibility, sensing ability, and automation for various parameter detection. Besides, the continuous exploration of droplet manipulation has led to the emergence of a wide variety of manipulation methods. Meanwhile, electrowetting that utilizes external fields modifying liquid–solid surfaces has found its applications in various areas, including droplet transportation, microfabrication, and healthcare. The energy generation from water droplets also presents exciting opportunities for the development of novel electricity generators. These approaches for droplet utilization underscore the immense potentials and versatilities of droplet-based technologies in the IoT landscape. Hence, this mini review presents the fundamental droplet-based technologies by summarizing their working mechanisms and methods, device structures, and applications. Given the challenges in materials, fabrication, and system integration, this review shows the overall development roadmap in terms of improved functionality and performance and highlights the opportunities toward multifunctional, self-sustainable, and intelligent systems, which is called for IoT construction.

Numerous natural and industrial processes entail the spontaneous entrapment of gas/air as rough/patterned surfaces are submerged under water. As the wetting transitions ensue, the gas diffuses into the water leading to the fully water-filled state. However, the standard models for wetting do not account for the microtexture's topography on collective wetting transitions. In other words, it is not clear whether the lifetime of n cavities arranged in a one-dimensional (I-D) line or a two-dimensional (II-D) (circular or square) lattice would be the same or not as a single 0-D cavity. In response, we tracked the time-dependent fates of gas pockets trapped in I-D and II-D lattices and compared them with wetting transitions in commensurate 0-D cavities. Interestingly, the collective wetting transitions in the I-D and the II-D arrays had a directionality such that the gas from the outermost cavities was lost the first, while the innermost got filled by water the last. In essence, microtexture's spatial organization afforded shielding to the loss of the gas from the innermost cavities, which we probed as a function of the microtexture's pitch, surface density, dimensionality, and hydrostatic pressure. These findings advance our knowledge of wetting transitions in microtextures and inspiring surface textures to protect electronic devices against liquid ingression.

Varying the chemical consistency of acoustically levitated droplets opens up an in situ study of chemical and biochemical reactions in small volumes. However, the optimization of the mixing time and the minimization of the positional instability induced by solution dispensing are necessary for practical applications such as the study of the transient state of macromolecules crystallography during the ligand binding processes. For this purpose, we study the inertial mixing in a configuration compatible with the room-temperature crystallography using the acoustic levitation diffractometer, therein solution drops ejected at high velocity collide and coalesce with droplets dispensed on acoustically levitated and rotating polymer thin-film sample holders. With the proposed method, we are able to achieve the mixing time of ∼0.1 s for sub-micro and a few microliter droplets. The observed short mixing time is ascribed to the rapid penetration of the solution into the droplets and confirmed by a computational fluid dynamic simulation. The demonstrated accelerated solution mixing is tested in a pilot time-lapse protein crystallography experiment using the acoustic levitation diffractometer. The results indicate the detection of transient ligand binding state within 2 s after the solution dispensing, suggesting the feasibility of the proposed method for studying slow biochemical processes.

There has been significant interest in researching droplet transport behavior on composite wetting surfaces. However, current research is primarily focused on modifying individual droplets and lacks an in-depth investigation into high-precision droplet storage. This study introduces a “billiard ball” droplet transport and storage platform (TSP) with differentiated areas. Within this platform, the volume of droplets stored in the area reaches a consistent threshold through droplet “scrambling,” inspired by the water-gathering behavior of spiders. The TSP involves connecting two regions of different sizes using a three-dimensional stepped wedge angle structure. However, this connection is not seamless, leaving a 2-mm gap between the regions. This gap is intentionally designed to enable continuous droplet transfer while preventing any static migration. Through systematic experimental and simulation analysis, we investigated the influence of superhydrophilic pattern structures and parameters on quantitative droplet storage. We established a functional relationship between the pattern area and the stored volume, and analyzed the intrinsic mechanism of droplet collision separation. This enabled us to achieve on-demand quantitative droplet storage and autonomize the storage process. The “billiard ball” droplet transport–storage platform proposed in this study holds promising applications in the fields of biomedical and organic chemistry.