Liquid marbles (LMs) have become a focal point in microfluidics for their efficient manipulation of small liquid volumes. These non-wetting droplets, typically coated with hydrophobic particles, offer enhanced stability, reduced evaporation and diverse utility, distinguishing them from bare droplets. This review examines advancements in LMs from 2014 to 2024, focusing on their rapid formation, robust manipulation, and revolutionary applications—termed the “3R trilogy.” We delve into the generation mechanisms, analyzing laboratory and engineering production techniques, and explore how surface particles affect LMs’ physicochemical properties. The structural dynamics and motion control of LMs are investigated, detailing their response to external forces and environmental factors. The review also highlights the state-of-the-art applications of LMs in digital microfluidics, biochemical analysis, materials synthesis, environmental monitoring, soft robotics, and energy harvesting. Concluding with a discussion on significant progress and future development trends, this review provides insights and ideas for broader applications of LM-based microfluidic platforms.

Droplet impact on solid surfaces is widely involved in diverse applications such as spray cooling, self-cleaning, and hydrovoltaic technology. Maximum solid‒liquid contact area yielded by droplet spreading is one key parameter determining energy conversion between droplets and surfaces. However, for the maximum deformation of impact droplets, the contact length and droplet width are usually mixed indiscriminately, resulting in unignored prediction errors in the maximum contact area. Herein, we investigate and highlight the difference between the maximum contact length and maximum droplet width. The maximum droplet width is never smaller than the maximum contact length, and the difference appears once the contact angle exceeds 90° (which becomes more significant on superhydrophobic surfaces), regardless of impact velocities, liquid viscosities, and system scales (from macroscale to nanoscale). A theoretical model analyzing the structure of the spreading rim is proposed to demonstrate and quantitatively predict the above difference, agreeing well with experimental results. Based on molecular dynamics simulations, the theoretical analysis is further extended to the scenario of nanodroplets impacting on solid surfaces. Reconsideration on the maximum deformation of impact droplets underscores the often-overlooked yet significant difference between maximum values of contact length and droplet width, which is crucial for applications involving droplet‒interface interactions.

The development of 3D cell culturing toward labor saving and versatility is highly desired. Here, we propose a platform consisting of a multiwell plate and liquid marbles (LMs). The inner walls of the plate are covered with particle-detachable superhydrophobic coatings that serve as both the substrates and particle sources for LM production. A produced LM, which serves as a minireactor for the 3D culture, features a monolayer nanoparticulate shell and naked-droplet-like transparency. The LM-in-plate platform provides a double-superhydrophobic environment that increases the stability of the 3D culture and reduces the necessary operational cautions. In addition, both cell observation and high-throughput applications can be conducted in situ, owing to the high LM transparency and the multiwell structure, respectively. This platform integrates the advantages of naked droplets (transparent and clean), LMs (stable non-wetting), and multiwell plates (high-throughput capability) and thus is promising for labor-saving and versatile 3D culturing.

Liquid directional transport surfaces have the ability to control the movement of liquids in specific directions, making them highly applicable in various fields such as heat transfer, fluid management, microfluidics, and chemical engineering. This review aims to summarize the research progress on liquid directional transport surfaces and spacecraft fluid management devices. Among the different liquid control technologies available, certain surface design methods based on principles of fluid dynamics under microgravity show remarkable potential for space fluid management. Precise fluid management is crucial for the in-orbit operation of spacecraft. Utilizing surface tension effects represents the most direct and effective approach to achieve directional liquid transport in space. The intrinsic flow characteristics of the two-dimensional plane of directional transport surfaces are advantageous for managing fluids in the confined spaces of spacecraft. By analyzing the functional characteristics of these liquid directional transport surfaces, we assess their feasibility for integration into spacecraft fluid management devices. Considering the features of the space environment, this review also provides design guidelines for liquid directional transport surfaces suitable for use in spacecraft fluid management devices, serving as a significant reference for future research.

Fog collection can be an affordable, practical solution to water scarcity in many regions around the world. Commercial fog harvesters typically use mesh structures composed of cylindrical wires or thin strips. The choice of their length scale, especially the width, has been a challenge due to a trade-off problem—wide wires or strips cause fog droplets to avoid contact and display lower deposition efficiency, while meshes comprising thin cylinders or strips often suffer from clogging and exhibit low drainage efficiency. In this study, we propose a cost-effective dual-scale structure, a vertical core composed of two twisted cylindrical wires surrounded by thin hairs protruding along radial direction, which can greatly improve the water collection efficiency by decoupling the mechanisms for droplet deposition and drain: while thin hairs allow fog droplets to retain high Stokes number and deposit with high efficiency, a vertical core functions as a wicking mechanism for deposited droplets to drain quickly. Fabricated hairy wires have a water collection rate of more than two and a half times that of smooth cylindrical wires of the same diameter, and their steady-state performance does not suffer from clogging, in contrast to conventional meshes composed of thin wires. Proposed hairy wires can be mass-produced by slightly modifying commercial products. This study provides a practical solution for the optimal design of fog collectors, benefiting the fight against the global water crisis.

Compartmentalization in living systems, where multiple reactions occur in parallel within confined spaces, has inspired the development of droplet networks in the past decade. These fascinating assemblies offer unique and versatile functions that are unattainable by single droplets and have shown their potential as advanced platforms for chemical and biological applications. This review highlights recent progress in the creation and application of droplet networks, covering strategies for generating the droplets and assembling them into functional networks. Key applications such as microreactors, signal conductors, actuators, and power sources are summarized. We also discuss the challenges and future trends in this field, aiming to narrow the gap between fundamental research and real applications.

Bubble growth kinetics has been attracting vast attention in water electrolysis and other gas evolution reactions, but mostly investigated under ambient pressure. For practical scenarios, bubble evolution is usually carried out under high pressure. To better understand the bubble growth kinetics, we monitored the hydrogen bubble evolution process at increased pressures during electrochemical hydrogen production. Unlike the common sense that high pressures could result in smaller bubble size, our results revealed that the increased pressure would increase the aerophilicity of electrode surface, with decreased bubble contact angle from 111° to 89° for 0.1‒2.0 MPa, increased detachment size from 233 to 1207 µm, and reduced growth coefficient from 230 to 10.9 for the high pressures from 0.1 to 3.0 MPa. The steady high-pressure bubble growth kinetics are basically governed by the as-formed supersaturation in bulk solution, which is the balance between the driving force (current density) and the enlarged solubility of bulk solution under high pressure. Insufficient driving force would induce the depletion of bulk supersaturation and stagnate the bubble growth. Further investigation on high-pressure bubble evolution behaviors should shed light on practical industrial electrode design with extended usage life.

Droplets are ubiquitous in nature and play an essential role in spray cooling, which is a highly efficient cooling approach for high-power-density miniaturized electronic devices. However, conventional pressure-driven spray faces significant challenges in controlling microdroplet characteristics, particularly the droplet size and spray direction, both of which critically impact cooling performance. Herein, to conquer these challenges, we designed an acoustic microdroplet atomizer composed of a lead zirconate titanate (PZT) transducer and silicon inverted pyramid nozzles. This design enables precise control of droplet generation, overcoming the limitations of traditional spray methods. The acoustic atomization technology minimizes excess liquid accumulation while significantly enhancing thin liquid film evaporation. Compared to the conventional droplet generation techniques such as pressure-driven, injector-based, and piezoelectric spray, our acoustic atomizer achieves superior cooling performance. Notably, we demonstrate a high heat flux of ∼220 W/cm² with a 3.6-fold enhancement at a low flow rate of 24 mL/min, achieving significantly improved cooling efficiency. Finally, our acoustic atomizer provides precise control over droplet size, velocity, and flow rate by adjusting the number of nozzles and the PZT transducer's resonant frequency, elevating spray cooling performance. This novel acoustic atomization cooling technology holds great promise for practical applications, particularly in the thermal management of compact electronic components.

Achieving mobile liquid droplets on solid surfaces is crucial for various practical applications, such as self-cleaning and anti-fouling coatings. The last two decades have witnessed remarkable progress in designing functional surfaces, including super-repellent surfaces and lubricant-infused surfaces, which allow droplets to roll/slide on the surfaces. However, it remains a challenge to enable droplet motion on hydrophilic solid surfaces. In this work, we demonstrate mobile droplets containing ionic surfactants on smooth hydrophilic surfaces that are charged similarly to surfactant molecules. The ionic surfactant-laden droplets display ultra-low contact angle and ultra-low sliding angle simultaneously on the hydrophilic surfaces. The sliding of the droplet is enabled by the adsorbed surfactant ahead of three-phase contact line, which is regulated by the electrostatic interaction between ionic surfactant and charged solid surface. The droplet can maintain its motion even when the hydrophilic surface has defects. Furthermore, we demonstrate controlled manipulation of ionic surfactant-laden droplets on hydrophilic surfaces with different patterns. We envision that our simple technique for achieving mobile droplets on hydrophilic surfaces can pave the way to novel slippery surfaces for different applications.