Droplet最新文献

Harvesting renewable water energy in various formats such as raindrops, waves, and evaporation is one of the key strategies for achieving global carbon neutrality. The recent decade has witnessed rapid advancement of the droplet-based electricity generator (DEG) with a continuous leap in the instantaneous output power density from 50 W/m² to several kW/m². Despite this, further pushing the upper limit of the output performance of DEG is still constrained by low surface charge density and long precharging time. Here, we report a DEG incorporating the Kelvin water dropper (K-DEG) that can generate an ultrahigh instantaneous power density of 10⁵ W/m² upon one droplet impinging. In this design, the Kelvin water dropper continuously replenishes the high density of surface charges on DEG, while DEG fully releases these surface charges into electric output. K-DEG with such a high output can directly light five 6-W commercial lamps and even charge a cellphone by using falling droplets.

Controlling acoustic streaming inside a droplet has excellent potential for enabling fluid and particle operations such as mixing, separation, and aggregation in various applications. Most concepts for generating surface acoustic waves are based on the placement of an interdigitated transducer at the side of a droplet, thus externally acting on the droplet. In this case, the flow structure inside the droplet is controlled by the relatively large scale of the interdigitated transducer compared to the droplet, thus limiting the local control of the flow. One possibility to overcome this drawback is to reduce the size of the actuator such that a highly focused ultrasound transducer can induce localized acoustic streaming in space. Here, we introduce a micro-spiral interdigitated transducer smaller than a droplet size that can generate micro-size vortices inside the droplet. This step enables a new way of controlling the flow inside the droplet, facilitating mixing, separation, aggregation, and patterning of particles. We study the characteristics of the acoustic streaming and the potential application of the flow for the separation and patterning of particles. The simplicity of the concept provides in-droplet particle manipulation toolsets for many applications such as biosensing, microbiology, and point-of-care devices.

Precise control of the evaporation of multiple droplets on patterned surfaces is crucial in many technological applications, such as anti-icing, coating, and high-throughput assays. Yet, the complex evaporation process of multiple droplets on well-defined patterned surfaces is still poorly understood. Herein, we develop a digital twin system for real-time monitoring of key processes on a droplet microarray (DMA), which is essential for parallelization and automation of the operations for cell culture. Specifically, we investigate the evaporation of multiple nanoliter droplets under different conditions via experiments and numerical simulations. We demonstrate that the evaporation rate is not only affected by the environmental humidity and temperature but is also strongly linked to the droplet distribution on the patterned surfaces, being significantly reduced when the droplets are densely distributed. Furthermore, we propose a theoretical method to aid in the experimental detection of volumes and pH variation of evaporating droplets on patterned substrates. This versatile and practical strategy allows us to achieve active maneuvering of the collective evaporation of droplets on a DMA, which provides essential implications for a wide range of applications including cell culture, heat management, microreactors, biochips, and so on.

Liquid–liquid phase separation in a biotic cell system organizes complicated biochemical reactions and functions by forming membraneless compartments that allow a substrate to move across the phase boundary. On the other hand, liquid–liquid phase separation in an abiotic system gives rise to an emulsion and/or multiple droplets that hardly undergo chemical reactions. We have developed a method for the formation of phase-separated multiple droplet in a ternary mixture with a 3D-printed microchannel and demonstrated the occurrence of the iron(III) thiocyanate ligand exchange reaction in the multiple droplet. The reaction proceeded differently in the outer- and the inner-droplet phases, giving a different iron(III) complex that was identified on the basis of its color change. Surprisingly, the color change was dynamic, enabling visualization of the interphase mass transfer. At the same time, the color change dynamics synchronized with the multiple-droplet movement.

Liquid biopsy, a noninvasive technique to obtain tumor information from body fluids, is an emerging technology for cancer diagnosis, prognosis, and monitoring, providing crucial support for the realization of precision medicine. The main biomarkers of liquid biopsy include circulating tumor cells, circulating tumor DNA, microRNA, and circulating tumor exosomes. Traditional liquid biopsy detection methods include flow cytometry, immunoassay, polymerase chain reaction (PCR)-based methods, and next-generation sequencing (NGS)-based methods, which are time-consuming, labor-intensive, and cannot reflect cell heterogeneity. 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.

Inside Back Cover: The cover image is based on the Review Article Hydrodynamic metamaterials: Principles, experiments, and applications by Chen et al.

This cover highlights diverse hydrodynamic metamaterials with versatile applications. These materials show great potential in drag reduction, advanced drug delivery, microfluidic device design, and tissue engineering. The review explores various design principles and the wide-ranging possibilities offered by hydrodynamic metamaterials in these fields. (DOI: 10.1002/dro2.79)

Front Cover: The cover image is based on the Review Article New insights into the interactions between two-dimensional ice and two-dimensional materials by Thi et al.

Controlling water droplet to two-dimensional (2D) ice transition by temperature at interface with the 2D layer materials enable multiple processes including cleaning surface, achieving high-yield instant transfer, and reducing friction for tribological applications. (DOI:10.1002/dro2.88)

Inside Front Cover: The cover image is based on the Research Article Liquid encapsulation in a freezing sessile drop by Lyu et al.

This paper demonstrates 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, which changes the final outcome of a freezing drop. This study highlights the importance of considering the properties of the environmental medium and provides novel strategies to manipulate a freezing drop. (DOI: 10.1002/dro2.90)

Back Cover: The cover image is based on the Review Article Building block copolymer particles via self-assembly within a droplet by Zhang et al.

The self-assembly of block copolymers within emulsion droplets is a flexible strategy for the preparation of polymer particles. This review systematically delves into the multiple mechanisms that drive BCP self-assembly within emulsion droplets, discusses various applications of BCP particles across multiple disciplines, and presents an overview of the current challenges and future directions for BCP emulsion self-assembly. (DOI: 10.1002/dro2.81)

Frontispiece: The cover image is based on the Research Article Two modes of contact-time reduction in the impact of particle-coated droplets on superhydrophobic surfaces by Lathia et al.

Micro-nano hydrophobic particle-coated droplets, known as liquid marbles (LM), can reduce impact contact time. This paper identifies two distinct modes of contact time reduction, namely, adhesion mode and fragmentation mode which are responsible for up to 65% reduction as compared to a bare droplet impact. (DOI: 10.1002/dro2.89)