Droplet最新文献

Hydrogel microcapsules are powerful microreactor vessels that have attracted widespread attention and research. Among the various methods for their generation, the aqueous two-phase system (ATPS) is by far the most straightforward approach. However, the high viscosity of ATPS solutions significantly limits the generation throughput of hydrogel microcapsule. In this study, we developed a novel high-throughput approach for generating hydrogel microcapsules using a microfluidic bubble-triggering strategy. By integrating constant-pressure air flow with droplet microfluidics devices, we efficiently manipulated the formation of ATPS droplet through bubble-induced Rayleigh-Plateau instability, enabling the production of uniform, monodisperse microcapsules. Additionally, the droplet generation frequency in the bubble-triggering method exceeded 36 kHz. We further demonstrated the encapsulation of genetically engineered Escherichia coli strains, which acted as biosensors for arsenic ions and caprolactam, highlighting the potential of these microcapsules for biosensing applications. This advancement in hydrogel microcapsule generation offers promising implications for scalable applications in biosensing, organoid culture, and high-throughput screening.

We report on the dielectrowetting of sessile droplets of two common liquid crystals, 4-cyano-4′-pentylbiphenyl (5CB) and 4-cyano-4′-n-octylbiphenyl (8CB), deposited on interdigitated electrodes that were treated to induce homeotropic anchoring. We found a pronounced hysteretic response of the contact angle to the applied voltage caused by the pinning and depinning of the droplet contact line. Depinning occurred as the voltage exceeded a threshold value that increased from the nematic to the isotropic phase, whereas the smectic phase showed an intermediate value. Above the threshold, the contact angle decreased linearly and rapidly as a function of the voltage square, as expected from the dielectrowetting equation originally formulated for dielectric and isotropic liquids, with a slope larger in the anisotropic liquid crystal phases than in the isotropic phase. Observation between crossed polarizers showed that the molecular director realigned along the applied field in the anisotropic phase near the surface between the electrodes, thereby increasing the effective dielectric constant and strengthening the dielectrophoretic force compared to the isotropic phase. Director realignment involved the nucleation of topological defects in the nematic phase and was inhibited by large energy barriers in the smectic phase, which weakened the dielectrowetting response.

Ambient energy harvesting from various renewable sources, including solar, thermal, wave, droplet, wind, and biomechanical energy, presents a promising solution for sustainable power generation and battery-free Internet of Things networks. However, these technologies face significant challenges in energy conversion efficiency and device durability due to environmental factors such as surface contamination, moisture accumulation, and biofouling. Superhydrophobic surfaces address these limitations through their unique properties of self-cleaning, water-repellent, and anti-bacterial, significantly enhancing energy harvesting performance and reliability. This review systematically summarizes recent advances in superhydrophobic surface-enhanced energy harvesting devices based on various mechanisms, including photovoltaics, electromagnetism, piezoelectricity, triboelectricity, thermoelectricity, and electrical double-layer dynamics. We first provide an updated overview of superhydrophobic surfaces, including their design strategies and fabrication methods. Then, we offer a comprehensive summary of their role in optimizing various energy harvesting devices. Finally, we discuss prospective challenges, potential solutions, and recommendations for future developments within this emerging interdisciplinary field.

Wang G, Hong M, Yang C, et al. Biomimetic chloroplasts: Two-phase microfluidic platforms with selective permeability for artificial photosynthesis. Droplet. 2025; 4(4): e70019. https://doi.org/10.1002/dro2.70019

The corresponding author information in the published version was incomplete due to an oversight during submission. The correct corresponding authors are

Prof. Xuming Zhang

Department of Applied Physics

The Hong Kong Polytechnic University, Hong Kong 999077, China

Email: [email protected]

Prof. Xiaowen Huang

Institute of Brain Science and Brain-Inspired Research

Shandong First Medical University & Shandong Academy of Medical Sciences, Jinan 250000, China

Email: [email protected]

Prof. Yaolei Wang

School of Life Science and Engineering

Southwest Jiaotong University, Chengdu 611756, China

Email: [email protected]

The authors apologize for this error and any inconvenience this may have caused.

The motion of contact line plays a crucial role in both natural phenomena and industrial processes. While it is well known that surface defects influence contact line dynamics, we demonstrate that their impact depends not only on geometry, size, and composition, but also on the history of fluid interaction with the surface. Using ultrafast, high-resolution reflection microscopy, we visualized the dynamics of the three-phase contact line as successive water droplets slid across a hydrophobic surface patterned with protrusions. We observed a growing attraction between the contact line and surface defects with increasing drop number. This effect arises from the spontaneous electrification that occurs during sliding: the droplets and the surface acquire opposite charges, generating electrostatic forces that significantly influence both advancing and receding contact lines. These forces contribute more than half of the total pinning force. Our findings reveal a previously overlooked factor in drop sliding and offer new insights into the dynamics of the contact line.

Inside Front Cover: The cover image is based on the Review Article Phenomenological contact line friction coefficient by Shen et al.

Cover description: The cover art illustrates a droplet dynamically wetting a solid surface with nano/microstructures, where contact line friction plays a dominant role. This review discusses the phenomenological contact line friction coefficient-a key parameter linking microscopic energy dissipation at the contact line to macroscopic wetting dynamics-and details its quantification methods and dependence on surface and liquid properties. (DOI: 10.1002/dro2.70030)

Inside Back Cover: The cover image is based on the Research Article Surfactant-mediated electro-dewetting of droplets in oil for liquid-shape manipulation by Wang et al.

Cover description: This work reports the first surfactant-mediated electro-dewetting of liquid droplets in oil. The cover illustrates that surfactant-laden droplets are manipulated by electric field to induce significant shape changes in an oil environment. Notably, contact-angle change of 100 degrees is obtained for electro-dewetting of a dimethyl sulfoxide (DMSO) droplet in hexadecane oil with mere 4 V. (DOI: 10.1002/dro2.70033)

Back Cover: The cover image is based on the Research Article Bubble pinch-off on biphilic and superhydrophobic surfaces by Ling et al.

Cover description: The pinch-off of bubbles from diverse surfaces—including superhydrophobic, biphilic, hydrophilic, and nozzle surfaces—follows the same underlying dynamics. In all cases, the time evolution of the neck is governed by liquid inertia, while bubble size and contact line behavior exert negligible influence on the pinch-off process. The neck size follows a universal power-law relations. (DOI: 10.1002/dro2.70021)

Front Cover: The cover image is based on the Research Article Solidification characteristics of two-dimensional water droplets by Song et al.

Cover description: This cover image illustrates trapped air bubbles in a solidified two-dimensional water droplet. Our study visualizes dendritic growth, freezing front profile evolution, internal temperature distribution, and trapped air bubble formation during droplet solidification. The findings are expected to enhance the understanding of three-dimensional water droplet solidification and provide valuable insights for investigating solidification phenomena in other materials. (DOI: 10.1002/dro2.70031)

The capability to manipulate liquid shape at the microscale has enabled numerous microfluidic devices. Due to its simple electric actuation, electrowetting-on-dielectric has been widely used in a variety of microfluidic applications that require reversible liquid-shape modulation. However, its use of dielectric and hydrophobic layers raised operation voltage, caused reliability issues, and increased fabrication cost. As an alternative mechanism, ionic-surfactant-mediated electro-dewetting has recently been demonstrated to enable digital microfluidics in air with a much lower voltage, higher reliability, and simpler chip fabrication. However, electro-dewetting for liquid-shape manipulation has remained poorly explored due to its limited contact-angle changes. Here, we investigated electro-dewetting in oil by testing various droplet liquids and hydrophilic substrate materials. To guide device development, cationic surfactants with varying hydrocarbon chain lengths and concentrations are tested. A contact-angle change of 100° is obtained for electro-dewetting of a dimethyl sulfoxide droplet in hexadecane with mere 4 V. To evaluate the utility of electro-dewetting in oil, proof-of-concept devices are assembled to explore the potential in optical applications such as reflective displays and liquid lenses. Compatible with various liquids and substrates, electro-dewetting with the liquid-in-oil configuration opens a door for simpler and more reliable microfluidic devices.