Droplet最新文献

Inside Back Cover: The cover image is based on the Research Article High-throughput generation of aqueous two-phase microcapsules using microfluidic bubble triggering by Rao et al.

Cover description: This cover image illustrates the rapid generation of aqueous two-phase droplets enabled by air-assisted microfluidics. The introduction of air bubbles imposes additional mechanical perturbations on the highly viscous aqueous phases, greatly facilitating droplet breakup and formation. Upon generation, the droplets spontaneously adopt a core–shell architecture, which can be subsequently converted into stable microcapsules through UV-induced gelation. These microcapsules provide a robust and versatile platform for biosensing, organoid culture, and high-throughput screening applications. (DOI: 10.1002/dro2.70034)

Back Cover: The cover image is based on the Review Article Strategies for achieving real-world robustness in topologically engineered surfaces with special wettability by Siu et al.

Cover description: Engineered topologies on surfaces with special wettability provide tailored functionalities and precise control over wetting and droplet behaviors, setting them apart from randomly structured surfaces. This review specifically addresses their critical durability challenges in real-world scenarios. It analyzes robust design principles and strategies to enhance longevity, providing a roadmap for sustaining functionality in demanding outdoor, underwater, and specialized practical applications. (DOI: 10.1002/dro2.70040)

Front Cover: The cover image is based on the Research Article When contact lines remember: Surface charge and the evolving interaction with defects by Xiang et al.

Cover description: This cover depicts a sliding droplet whose advancing contact line is pulled toward a surface defect by spontaneous electrification prior to physical contact. In this study, ultrafast, high-resolution microscopy reveals history-dependent contact-line dynamics driven by surface charges, uncovering an overlooked electrostatic mechanism in dynamic wetting. These insights pave the way for programmable wettability and advanced droplet control. (DOI: 10.1002/dro2.70039)

Inside Front Cover: The cover image is based on the Research Article Droplet manipulation enabled by bio-inspired high-aspect-ratio micropumps via mold-assisted microfabrication by Mao et al.

Cover description: The cover illustrates a bio-inspired electrohydrodynamic (EHD) micropump featuring high-aspect-ratio electrodes developed via a novel mold-assisted microfabrication strategy. This device enables precise on-chip droplet manipulation. The background digital stream represents the integration of machine learning algorithms, which are employed to model droplet generation dynamics and optimize the system's performance parameters. (DOI: 10.1002/dro2.70049)

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.

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.

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 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.

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.