Contactless, spatiotemporal droplet maneuvering plays a critical role in a wide array of applications, including drug delivery, microfluidics, and water harvesting. Despite considerable advancements, challenges persist in the precise transportation, splitting, controlled steering, and functional adaptability of droplets when manipulated by electrical means. Here, we propose the use of orbital electrowetting (OEW) on slippery surfaces to enable versatile droplet maneuvering under a variety of conditions. The asymmetric electrowetting force that is generated allows highly efficient droplet manipulation on these surfaces. Our results demonstrate that droplets can be split, merged, and steered with exceptional flexibility, precision, and high velocity, even against gravity. Additionally, the OEW technique facilitates the manipulation of droplets across different compositions, volumes, and arrays in complex environments, leaving no residue. This novel droplet maneuvering mechanism and control strategy are poised to impact a range of applications, from chemical reactions and self-cleaning to efficient condensation and water harvesting.

Liquid film cooling serves as a critical thermal protection mechanism in rocket thrusters. The interaction between oxidizer droplet, which is deposited from mainstream region of thrust chamber, and fuel film on the wall inevitably influences cooling efficiency, which is poorly understood in existing research. This study experimentally investigated hypergolic reaction between white fuming nitric acid droplet and ionic liquid fuel film at elevated wall temperature T_w using synchronized high-speed and infrared thermography. Results show that reaction progresses through inertia-dominant spreading, mixing, and culminates in intense liquid-phase explosion (micro-explosion). An elevated T_w intensifies micro-explosion, increasing the risk of wall exposure and leading to the decline of cooling efficiency. Paradoxically, the increase in local film temperature inversely correlates with T_w, which is related to reduced explosion delay time. These findings first provide thermal and hydrodynamic data essential for the design of future thermal protection measures for small hypergolic liquid rocket thrusters and offer theoretical basis for optimizing liquid film cooling systems in bipropellant propulsion architectures.

Emulsions are inherently thermodynamically unstable dispersions that are widely involved in food processing, cosmetic preparation, and drug delivery. The existing ultrasonic emulsification techniques mainly rely on the direct contact between the sonicator probe and liquids, which causes localized high temperature and pressure within the liquid and influences the final properties of the obtained emulsion. In this work, a containerless emulsification approach has been realized by using ultrasonic levitation. The emulsification of water‒oil system can be promoted by adjusting the emitter‒reflector distance to alter the acoustic radiation pressure on the surface of the levitated drop. The dynamic behaviors of the emulsification process were monitored by using a high-speed camera, and the sound field was analyzed via numerical simulation. The experimental results showed that atomization of droplets driven by sound field was the main driving force for emulsification. This method can be used to prepare emulsions in which the average diameter of the droplets was about 2–3 µm. The work provided a new method for containerless emulsification, thus shedding light on the preparation of contamination-free pharmaceuticals.

Symmetry typically characterizes the impact of a liquid droplet on a solid surface, where uniform spreading is followed by radial retraction. Breaking this symmetry traditionally relies on engineering surface properties. Here, we introduce an alternative approach to achieve asymmetric droplet impact by incorporating a pair of bubbles into the liquid droplet, resulting in the coexistence of spreading and retraction. The asymmetric dynamics originate from the anisotropic capillary effects that can be adjusted by varying the volume fraction of bubbles and the impact velocity. The early onset of retraction enhances upward liquid momentum, facilitating prompt droplet takeoff and significantly reducing both the contact area (up to 50%) and contact time (up to 60%). This reduction also diminishes heat exchange between the droplet and the surface. Our findings pave the way for applications that capitalize on reduced contact times through droplet engineering, eliminating the need for surface modifications.

We analytically describe the slip length of the surfactant-covered bubble film under the joint actions of pressure gradient and electric field. Considering the Marangoni effect, the slip length and consequent zeta potential of the liquid‒vapor interface significantly reduced compared to the Marangoni-free interface at low surfactant concentrations, due to the surfactant accumulation at downstream of the bubble liquid film. In addition, we discovered that the friction coefficient of the liquid‒vapor interface becomes field dependent in a regime of strong coupling among volume flow, surfactant transport, and ionic current at the liquid‒vapor interface. We use the Onsager reciprocal relationship to describe the electrokinetic effects within a bubble film, including flow velocity, ionic current, and surfactant transport, which can describe the Marangoni effects while considering multi-physical effects.

Droplet splitting technology presents considerable potential for advancing applications in sample encapsulation, manipulation, chemical reaction control, and precision measurement systems. However, existing methodologies frequently encounter limitations related to complex operation and high cost. To address the need for controllable, high-precision, and cost-efficient droplet splitting, this study combines three-dimensional printing technology with superhydrophobic surface modification to fabricate pyramid microstructures with customized splitting functionalities. The pyramidal sharp edges act as “fluidic blades” to split droplets through the synergistic interaction of edge-induced capillary forces and inertial forces generated at the liquid film periphery during spreading dynamics. Upon penetration by the pyramid apex, the droplet forms an annular liquid ring that subsequently fragments into sub-droplets, enabling programmable splitting. A comprehensive experimental and computational framework was developed to investigate splitting dynamics, force distribution patterns, and geometric dependence of pyramid structures on splitting performance. Results indicate that increased Weber numbers, larger droplet volumes, and reduced pyramid apex angles markedly improve splitting controllability. Additionally, six- and 12-sided pyramid-based splitting/collection devices were engineered to demonstrate practical implementations, including on-demand droplet splitting and liquid marble synthesis. This work establishes a scalable, low-cost platform for precision droplet manipulation with significant implications for microfluidic devices and lab-on-a-chip technologies.

The breakage of the cellular membrane for releasing intracellular material is the starting point for several diagnostics or treatment processes. Surface acoustic waves can provide a novel and chemical-free approach by inducing acoustic streaming generating high shear stress inside a droplet containing cells. However, the power required to achieve an efficient cell lysis can lead to the displacement of the droplet and even the nebulization of the droplet. This effect is aggravated as the droplet size is reduced. In this work, we demonstrate the possibility overcoming the mentioned issue by a micro-size aperture surface acoustic wave generator operating at high frequency. By reducing the aperture of the surface acoustic wave generator to a fraction of the diameter of the deposited droplet, the localized acoustic streaming can lead to high shear stress while not exceeding the adhesion force of the droplet preventing droplet motion or nebulization. This concept can lyse AC16 human cardiomyocyte cells with efficiencies of 80% comparable to a chemical lysis method in 60 s of exposure time.

Soft robots based on stimuli-responsive materials, such as those responsive to thermal, magnetic, or light stimuli, hold great potential for adaptive locomotion and multifunctionality in complex environments. Among these, liquid crystal elastomers (LCEs) and magnetic microparticles have emerged as particularly promising candidates, leveraging their thermal responsiveness and magnetic controllability, respectively. However, integrating these modes to achieve synergistic multimodal actuation remains a significant challenge. Here, we present the thermo-magnetic petal morphing robot, which combines LCEs with embedded magnetic microparticles to enable reversible shape morphing via remote light-to-thermal actuation and high-speed rolling locomotion under external magnetic fields. The robot can achieve rapid deformation under near-infrared light, transitioning from a closed spherical to an open cross-like configuration with consistent shape recovery across multiple cycles, and demonstrates a maximum locomotion speed of 30 body lengths per second, outperforming many state-of-the-art soft robots. Moreover, the robot's performance remains robust across dry, wet, and underwater conditions, with adjustable magnetic particle concentrations allowing tunable actuation performance. Our work addresses the need for soft robots with enhanced versatility and adaptability in complex environments, paving the way for applications in areas such as targeted drug delivery and industrial material handling.