Precise manipulation of droplets or bubbles hosts a broad range of applications for microfluidic devices, drug delivery, and soft robotics. Generally the existing approaches via passively designing structured surfaces or actively applying external stimuli, inherently confine their motions within the planar or curved geometry at a slow speed. Consequently the realization of 3D manipulation, such as of the underwater bubbles, remains challenging. Here, during the near-infrared-laser impacting on water, by simply introducing a thermally conductive interface, we unexpectedly observe a spontaneously bouncing bubble with hundreds-of-micrometer diameter at tens-of-Hertz frequency. The unique formation of temperature inversion layer in our system generates the depth-dependent thermal Marangoni force responsible for the bouncing behavior. Both the scaling analysis and numerical simulation agree with observations quantitatively. Furthermore, by controlling the navigation speed of the laser beam, the bubble not only shows excellent steerability with velocity up to 40 mm/s, but also exhibits distinctive behaviors from bouncing to dancing within water. We demonstrate the potential applications by steering the bubble within water to specifically interact with tiny objects, shedding light on the fabrication of bubble-based compositions in materials science and contamination removal in water treatment.

Multicomponent droplets are pertinent to diverse applications ranging from 3D printing to fabrication of electronic devices to medical diagnostics and are typically inherent with the occurrence of the phase transition in the manifestation of evaporation and solidification. Indeed, the versatile transformations and fascinating morphologies of the droplets have been identified, which primarily arise from the evaporation-induced flow. Here, we report the self-lifting behavior of a frozen binary droplet, resulting in a nearly doubling in height, in a fashion that defies against the gravitational effect. This counterintuitive observation is attributed to an internal solutal Marangoni flow up to $1\mathrm{mm}/\mathrm{s}$, which is driven by the enriched solute concentration locally in the vicinity of the solidification front. Moreover, we perform theoretical analysis by incorporating the propagation of solidification front, and the calculated spatiotemporal evolution of droplet shape agrees with experiments excellently. The effects of several key physical parameters on self-lifting are elucidated quantitatively, providing guidance to control the self-lifting. These results will further advance our understanding of underlying physicochemical hydrodynamics in the multicomponent liquid systems subjected to heat transfer and phase change, consequently shedding light on the relevant technological applications.

In this paper, the plasmonic resonant absorption of gold nanorods (GNRs) and GNR solutions was studied both numerically and experimentally. The heat generation in clustered GNR solutions with various concentrations was measured by exposing them to Near Infrared (NIR) light in experiment. Correspondingly, calculations based on the discrete-dipole approximation (DDA) revealed the same relationship between the maximum absorption efficiency and the nanorod orientation for the incident radiation. Additionally, both the plasmonic wavelength and the maximum absorption efficiency of a single nanorod were found to increase linearly with increasing aspect ratio (for a fixed nanorod volume). The wavelength of the surface plasmonic resonance (SPR) was found to change when the gold nanorods were closely spaced. Specifically, both a shift and a broadening of the resonance peak were attained when the distance between the nanorods was set to about 50 nm or less. The absorbance spectra of suspended nanorods at various volume fractions also showed that the plasmonic wavelength of the nanorods solution was at 780 ± 10 nm, which was in good agreement with the computational predictions for coupled side-by-side nanorods. When heated by NIR light, the rate of increase for both the temperature of solution and the absorbed light diminished when the volume fraction of suspended nanorods reached a value of $1.24\times {10}^{-6}$. This matches with expectations for a partially clustered suspension of nanorods in water. Overall, this study reveals that particle clustering should be considered to accurately gauge the heat generation of the GNR hyperthermia treatments.

Droplet impacting on the solid substrate, which typically is a simple planar surface, has been extensively studied for various technological applications. Here, through numerical calculation, we explore the droplet impacting on a single hemispherical bead and double bead structures. Several key physical parameters have been taken into account, including the Weber number, wettability, and geometry of microstructures. We reveal the spatiotemporal evolution of the droplet pattern, the correlated physical parameters, and the underlying physical mechanisms (air cushion or bubble). These results provide theoretical guidance to control jump-off forces via the structure design and suitable wettability for the relevant applications such as erosion protection.

In this work, we report the impacting and freezing dynamics when a hexadecane droplet impacts on a supercooled immiscible water pool. By utilizing the synchronized high-speed imaging and thermal imaging, three phases for the droplet dynamics have been identified: the jet phase, the flat phase, and the bowl phase. These different phases arise from the solidification process of the hexadecane droplet, and hence, depend on the degree of supercooling or water temperature. We further perform the scaling analysis for the phase transition, which agrees with the experimental observations remarkably. At a high Weber number, the transition between each phase is primarily determined by the supercooling temperature of the liquid pool.