Research Topics
Liquid repellent surface
Our major topic is to understand “How to prevent unwanted adhesion to surfaces”. Research targets are fingerprint, snow, mist, nucleated ice, fluidic food, polymer melt, biomaterials, and granular materials. The outcomes will offer us ideas to design functional non-adhesion surface materials. We are now in the stage of understanding the dynamics of their adhesion processes by integrating high-speed cameras with custom-built optical set-ups. One of our achievements is the design of super liquid-repellent coatings. The surface possesses both nano to micro-scale hierarchical structure and hydrophobic surface chemistry. Water droplets resting on this surface exhibit a water contact angle of ~170°, and they roll off this surface with small tilting of <5° without any adhesions. We expect this textile can be applied for non-fouling clothing industries, which leads to a significant decrease in laundry costs. Recently we are interested in the development of liquid marble and liquid-infused surface.
See Advanced Materials Interfaces (2022), Langmuir (2017) & Advanced Functional Materials (2016)
Superomniphobic surface
Super-liquid-repellent glass bottle
Anti-fogging slippery surface (SPLASH)
Multi-functional liquid slippery surface
Drycells: Micropowdering single-cells
We encapsulated cell-suspension microdroplets in hydrophobic nanoparticles to form "drycells". The drycells behave like a dry powder while containing >95% aqueous culture medium. Through adjustment of the formation parameters, cell encapsulation number, cell type heterogeneity, and colony localization number per cell can be regulated. The drycell would be a powerful tool for cell picking for high-level cell analysis.
Adaptive droplet
Generation of adaptive materials, which is one of the promising directions in materials science. Applying the jamming concept is effective for materials to have adaptivity. Jamming is a phase transition of granules between fluid-like plasticity or solid-like rigidity that does not rely on temperature changes, as in ordinary materials, but instead is controlled by packing fraction. In this project, hydrophobic particles are capillary trapped at liquid−air interface and their packing fraction is controlled to induce interfacial jamming. It is found that the shape and rheology of liquid droplets are tunable with the packing behavior of the interfacially adsorbed particles. Taking advantage of the jamming and wetting transition scenario, the droplets instantly change their macroscopic behavior from liquid-like wettable state to elastic or plastic soft solid state. This property may be suitable for smart materials with adaptive mechanical properties. We have unraveled the soft material characters and the transition by interfacial jamming, related functions, and some potential applications has been reported.
See Advanced Materials Interfaces (2020) & Advanced Functional Materials (2019)
Reversible jamming transition of adaptive droplet
Non-sticking droplet
Plastically deformed droplet
Wettable droplet
Preprogrammed death of floating droplet
Droplets covered with hydrophobic nanoclay collapse on the liquid pool with a specific lifetime. The lifetime of the droplet can be modulated over seconds to hours scale depending on the selection of chemically modulated wettability of the nanoclay. The critical mechanism of lifetime modulation is responsible for controlling the coalescence kinetics between the water pool and inner liquid by nanoclays’ high diffusion length and chemically varied water spreading potential.
Patchwork on droplets
Materials with a core-shell structure have been widely explored for applications in carrier systems. Liquid marble is one of the core-shell materials, which is formed by covering a fluid droplet with particles and is expected to be useful for various applications, especially in industrial and biomedical fields. We study the formation of multi-functional liquid marbles for practical applications. A wide variety of functional particles have been synthesized to form functional liquid marbles. However, the formation of multifunctional liquid marbles by integrating several types of functional particles is challenging. We recently reported a general strategy for the flexible patterning of functional particles on droplet surfaces. Based on this strategy, a single bi-functional liquid marble is designed from two mono-functional liquid marbles as an advanced droplet carrier. One of the serious issues in practical use for liquid marble is fragileness. We recently unraveled the dynamics of liquid marble breakage, which is classified into two scenarios. Based on these investigations, we proposed a way to improve the robustness of liquid marbles.
Multi-faced liquid marbles
Adaptive granular raft
Hydrophobic-particles-jammed film on the liquid pool is designed. The film can transport small objects adaptively irrespective of their state (gas/liquid/solid) by switching its state without hindrance from physical obstacles. The film also exhibits adaptive jamming transition for regeneration ability, obstacle penetration, and dispersed solids collection. This work contributes to the development of swarm biomimetics, object transportation, and adaptive materials.
Mechanics of droplet transportation
The transport of liquid droplets plays an essential role in various applications. Modulating the wettability of the material surface is crucial in transporting droplets without external energy, adhesion loss, or intense controllability requirements. Although several studies have investigated droplet manipulation, its design principles have not been categorized considering the mechanical perspective. Here, we categorized liquid droplet transport strategies based on wettability modulation into those involving (i) application of driving force to a droplet on non-sticking surfaces, (ii) formation of gradient surface chemistry/structure, and (iii) formation of anisotropic surface chemistry/structure. Accordingly, reported biological and artificial examples, cutting-edge applications, and future perspectives are summarized.
