Directional Liquid Transport from the Cold Region to the Hot Region on a Topological Surface

Dynamics of Pulsed-Laser Interaction with Janus Particles

Janus particles, with their flexible chemistry and multifunctionality, have broadened the scope of the optical manipulation field as an emerging class of materials. Laser-based manipulation is particularly promising for half-metal-coated particles, offering a platform to study optical and thermal effects. However, the role of the laser's operation regime in particle behavior needs to be understood better. Hence, in this work, we studied the interaction of nanosecond-pulsed lasers on 4.1 μm Au-Janus particles with a 100 nm gold cap. We focused on the interaction in three sections: (1) We observed three pulse energy influence regimes: In the low-influence regime (less than ∼10 nJ), the particle maintains its intrinsic Brownian motion. In the medium-influence regime (less than ∼40 nJ), the particle exhibits an extended range of motion. In the high-influence regime (higher than ∼40 nJ), the particle undergoes superdiffusion and establishes a new equilibrium position. (2) During optical manipulation trials, a threshold pulse energy of 4 nJ (average power of 40 μW) was sufficient to move Au-Janus particles against the laser spot. We achieved translation velocities of 0.9-5.1 μm/s at 4-50 nJ. (3) The gold cap is damaged at 20 nJ (fluence of 0.7 J/cm2) when the laser is focused on the particle, consistent with theoretical predictions, and the ablation process generates micro- and submicrometer gold particles. These findings reveal the potential of pulsed lasers for precise, power-efficient manipulation of Janus particles, advancing our understanding of laser-particle interactions and opening new pathways for optical manipulation applications.

A Review of Droplet/Bubble Transportation on Bionic Superwetting Surface

The controllable droplets/bubble transportation has a wide range of applications in the fields of biomedical, chemistry, energy, and material applications, and has aroused great attention for its significant scientific and technology importance. The main challenges derived from the liquid/solid or gas/solid contact strength and actuating energy input. Artificial superwetting surfaces inspired by nature creatures have triggered technology revolution in many fields relevant to droplet operation, and the applied actuating force improve the controllability to preferential direction. In this review, we highlights recent advancements in droplets/bubble transportation on the superwetting surfaces driven by passive or active stimulation methods inspired by bionic function interfaces. The three main superwetting surfaces including superhydrophobic surface, slippery liquid-infused porous surface, hybrid surface, various stimuli methods including gravity/buoyance, chemical/morphology gradient, heat, magnetism, electricity, light, adhesion force, and prosperous applications including micro-reaction, biochemical analysis, fog collection/antifog, energy transfer, bubble/liquid micro-robot, self-cleaning, light/circle switch have been systematically summarized. Finally, the challenges and future perspectives of research innovations and practical applications are discussed.

Gradient-Wettable Multiwedge Patterned Surface for Effective Transport of Droplets against the Temperature Gradient

With the rapid advancement of electronic integration technology, the requirements for the working environment and stability of the heat dissipation equipment have become increasingly stringent. Consequently, studying a high-efficiency gas-liquid two-phase heat transfer surface holds significant importance. Aiming at the limited liquid transport performance caused by the temperature gradient in the heat transfer process, this paper combines the wetting gradient with the shape gradient and proposes a gradient-wettable multiwedge patterned surface, where droplets can be transported over long distances and at high velocities. In this paper, the effect of the average wetting gradient on droplet transport performance is investigated by designing a multiwedge hydrophilic pattern and adjusting the wetting properties of the hydrophobic region. The study focuses on the temperature gradient resistance of gradient-wettable, multiwedge patterned surfaces, providing a mechanistic explanation of the surface's ability to resist temperature gradients through theoretical analysis. It is shown that the gradient wettability multiwedge patterned surface has better resistance to the temperature gradient that hinders the droplet movement, and the droplets can still achieve transport of ∼38 mm at an average speed of ∼158 mm/s under the temperature gradient of 0.59 °C/mm. The research in this paper provides some insights into the application of temperature gradient resistance on heat transfer surfaces and contributes to heat dissipation methods for electronic integrated environments.

Bioinspired functional SLIPSs and wettability gradient surfaces and their synergistic cooperation and opportunities for enhanced condensate and fluid transport

Bioinspired smart functional surfaces have received increasing attention in recent years owed to their tunable wettability and enhanced droplet transport suggesting them as excellent candidates for industrial and nanotechnology-related applications. More specifically, bioinspired slippery lubricant infused porous surfaces (SLIPSs) have been proposed for their low adhesion enabling continuous dropwise condensation (DWC) even of low-surface tension fluids. In addition, functional surfaces with chemical and/or structural wettability gradients have also been exploited empowering spontaneous droplet transport in a controlled manner. Current research has focused on the better understanding of the mechanisms and intimate interactions taking place between liquid droplets and functional surfaces or on the forces imposed by differences in surface wettability and/or by Laplace pressure owed to chemical or structural gradients. Nonetheless, less attention has been paid to the synergistic cooperation of efficiently driving droplet transport via chemical and/or structural patterns/gradients on a low surface energy/adhesion background imposed by SLIPSs, with the consequent promising potential for microfluidics and condensation heat transfer applications amongst others. This review provides a detailed and timely overview and summary on recent advances and developments on bioinspired SLIPSs and on wettability gradient surfaces with focus on their synergistic cooperation for condensation and fluid transport related applications. Firstly, the fundamental theory and mechanisms governing complex droplet transport on homogeneous, on wettability gradient surfaces and on inclined SLIPSs are introduced. Secondly, recent advances on the fabrication and characterization of SLIPSs and functional surfaces are presented. Then, the condensation performance on such functional surfaces comprising chemical or structural wettability gradients is reviewed and their applications on condensation heat transfer are summarized. Last a summary outlook highlighting the opportunities and challenges on the synergistic cooperation of SLIPSs and wettability gradient surfaces for heat transfer as well as future perspective in modern applications are presented.

Regular Self-Actuation of Liquid Metal Nanodroplets in Radial Texture Gradient Surfaces

Liquid metal movement in microfluidic devices generally requires an external stimulus to achieve its motion, which results in many difficulties to precisely manipulate its motion at a nanoscale. Therefore, there is an attempt to control the motion of a liquid metal droplet without the input of an external force. In this paper, we report an approach to achieve the self-actuation of a gallium nanodroplet in radial texture gradients on substrates. The results have proved the validity of this method. It is suggested that there are four stages in the self-motion of the droplet and that the precursor film forming on the second stage plays a pivotal role in the motion. Furthermore, how the impact velocity affects the self-actuation of the nanodroplet on the gradient surface is also studied. We find that the moderate impacting velocity hinders the self-actuation of the gallium nanodroplet. This study is very helpful to regulate the self-actuation on patterned substrates and facilitate their applications in the fields of microfluidics devices, soft robots, and liquid sensors.