Droplet impact dynamics on solid surfaces, which are ubiquitously present in aerospace engineering, energy systems, agricultural production, etc., involve complex fluid-structure interactions. Herein, we employ a single-camera high-speed three-dimensional digital image correlation system to quantify the full-field deformations of flexible thin films during droplet impact dynamics. Experimental results revealed that the substrate flexibility not only reduces the maximum spreading diameter by 10% but also modulates rebound dynamics via energy competition between kinetic energy and surface adhesion energy, suggesting that coupled deformation of the solid-fluid interface plays an important role in the dynamic progress. We propose the structure-coupled response number (Sn), a governing dimensionless parameter unifying droplet spreading on both rigid and flexible films, validated by a universal 1/2 scaling law. A theoretical criterion for droplet rebound on hydrophobic flexible thin films is derived and experimentally demonstrated, which achieves the precise control of droplet rebound/non-rebound mode. This work bridges the theories of droplet impact dynamics on rigid and flexible substrates, offering a robust strategy to govern the droplet impact behaviors.

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.

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.

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.

Highly ordered films of polystyrene (PS) micro-spheres have demonstrated various merits in optoelectronic devices, given their size- and thickness-dependent optical properties. So far, various solution strategies have been developed for making such highly ordered films, which have suffered from the lack of precise control on the film thickness (i.e., layer number of micro-spheres). Here, we developed a facile fibrous liquid bridge strategy for fabricating highly ordered PS micro-sphere films, featured as the finely tunable mono- to multi-layer. Guided by a horizontally placed fiber with both ends passing through a capillary tube, respectively, the solution was transferred steadily onto the target substrate forming a homogeneous liquid film, whose dewetting process thus confines the assembly of micro-spheres in a well-controllable manner. Depending on both the solution-shearing speed and the local concentration, a dynamic equilibrium between liquid transfer and evaporation was realized, which enables the formation of highly ordered micro-sphere films with finely tunable layer numbers. We demonstrated the angle-specific information encryption for anti-counterfeiting by utilizing patterned PS micro-sphere films that modulate structural colors based on layer-dependent optical responses. The result offers a new perspective for fabricating highly ordered film with tunable layers.

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.

Engineered topologies on superwetting with special wettability provide tailored functionalities and precise control over wetting and droplet behaviors, setting them apart from randomly structured surfaces. These features are crucial for applications requiring precision and efficiency, for example, directional droplet transport, anisotropic wetting, smart coating, thermal management, etc. Nonetheless, the reliance on engineered topographies renders these surfaces susceptible to structural damage, even at nano/micro-level, leading to functional deterioration in practical scenarios. This review specifically addresses durability challenges faced by the surfaces with engineered topologies, excluding random structures. We commence by examining robust strategies aimed at mitigating practical challenges encountered in real-world scenarios. Next, we outline the structural design principles that underpin these surfaces, integrating real-world examples from outdoor, underwater, and specialized applications are integrated to illustrate diverse approaches for tackling the multifaceted challenges. Finally, we analyze practical issues related to scaling up fabrication processes and identify areas for future research. By dissecting the intricate relationships between structural integrity, functional efficiency, and material selection, this review aims to provide a comprehensive understanding of durability issues. It also offers a strategic roadmap for enhancing the longevity of surfaces with special wettability in the real world, specifically focusing on those with engineered topologies while explicitly excluding random structures.

Nanodroplet impact on nanoscale material interfaces is widely involved in nanoscience and nanotechnology, affecting the technical reliability through complicated liquid‒solid interaction force, that is, the droplet impact force. However, our understanding of the nanodroplet impact force is still blank. Herein, we reveal that the nanoscale size (∼10 nm) and high impact velocity (>100 m/s) of nanodroplets lead to unique characteristics of impact force, significantly differing from those of macrodroplets (∼1 mm). The nanodroplet impact force profile holds a single-peak feature, which is independent of droplet parameters and material wettability. The significant water-hammer pressure induces the abnormal rising of impact force, yielding unexpectedly high peak values governed by the Mach number (more than 10 orders of magnitude higher than droplet gravity). Our findings of droplet impact force at the nanoscale reveal the potential challenge of the damage of material surfaces by nanodroplet impact, highlighting one crucial factor for advancing nanolithography and nanoprinting.

Droplet impact on solid surfaces plays a critical role in a wide range of applications, including inkjet printing, spray cooling, surface coatings, and microdroplet chemistry. Precise control of droplet-surface interactions is essential, but the fundamental mechanisms governing this process are still not fully understood. In this study, we demonstrate that large contact angle hysteresis (CAH) on hydrophobic nanoporous surfaces significantly amplifies post-impact droplet oscillations. This reveals the critical influence of CAH on the redistribution of impact energy and the modulation of droplet-surface interactions. Using shape mode decomposition via Legendre polynomials and fast Fourier transform spectral analysis, we show that surfaces with larger CAH excite and sustain higher-order droplet shape mode oscillations, leading to persistent capillary waves even after contact line pinning. The observed amplitude modulation and multiple frequency components within individual shape modes reveal nonlinear energy transfer between different modes. These amplified and coupled oscillations are shown to promote daughter droplet coalescence. This study presents a framework for understanding the role of CAH in storing and redistributing impact energy through nonlinear mode excitation and establishes CAH as a critical design parameter for controlling fluid dynamics on solid surfaces.

Miniaturized functional fluidic pumps have found broad applications across various fields; however, the fabrication and dimensional limitations of their electrodes remain a significant challenge. Conventional manufacturing techniques often fail to achieve high aspect ratio structures exceeding 2 and electrode heights greater than 1 mm. In this work, we propose a novel extreme microfabrication strategy that integrates flexible molding techniques with advanced microfabrication processes to develop high-precision pump electrodes. These electrodes are successfully implemented in droplet manipulation applications. First, we selected suitable microfabrication-compatible materials and developed a conductive, flexible liquid elastomer, along with a tailored fabrication process. Next, a functional working fluid compatible with the electrodes was synthesized and characterized in terms of its viscosity, electrical conductivity, dielectric constant, and interfacial behavior with aqueous phases. A corresponding microfluidic chip was also fabricated to assess its droplet generation performance. Both duty cycle-based and frequency-based droplet manipulation strategies were investigated using this chip. Finally, a machine learning approach was employed to model the droplet generation process and evaluate the influence of four key parameters on device performance. This study establishes a foundational platform and design pathway for future development of integrated on-chip pumping systems in microfluidic applications.

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: xuming.zhang@polyu.edu.hk

Prof. Xiaowen Huang

Institute of Brain Science and Brain-Inspired Research

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

Email: huangxiaowen2013@gmail.com

Prof. Yaolei Wang

School of Life Science and Engineering

Southwest Jiaotong University, Chengdu 611756, China

Email: wangyaolei@swjtu.edu.cn

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