Yosuke Tsuge

Controllable Broadband Optical Transparency and Wettability Switching of Temperature-Activated Solid/Liquid-Infused Nanofibrous Membranes

Inspired by biointerfaces, such as the surfaces of lotus leaves and pitcher plants, researchers have developed innovative strategies for controlling surface wettability and transparency. In particular, great success has been achieved in obtaining low adhesion and high transmittance via the introduction of a liquid layer to form liquid-infused surfaces. Furthermore, smart surfaces that can change their surface properties according to external stimuli have recently attracted substantial interest. As some of the best-performing smart surface materials, slippery liquid-infused porous surfaces (SLIPSs), which are super-repellent, demonstrate the successful achievement of switchable adhesion and tunable transparency that can be controlled by a graded mechanical stimulus. However, despite considerable efforts, producing temperature-responsive, super-repellent surfaces at ambient temperature and pressure remains difficult because of the use of nonreactive lubricant oil as a building block in previously investigated repellent surfaces. Therefore, the present study focused on developing multifunctional materials that dynamically adapt to temperature changes. Here, we demonstrate temperature-activated solidifiable/liquid paraffin-infused porous surfaces (TA-SLIPSs) whose transparency and control of water droplet movement at room temperature can be simultaneously controlled. The solidification of the paraffin changes the surface morphology and the size of the light-transmission inhibitor in the lubricant layer; as a result, the control over the droplet movement and the light transmittance at different temperatures is dependent on the solidifiable/liquid paraffin mixing ratio. Further study of such temperature-responsive, multifunctional systems would be valuable for antifouling applications and the development of surfaces with tunable optical transparency for innovative medical applications, intelligent windows, and other devices.

Slippery Liquid-Immobilized Coating Films Using in Situ Oxidation–Reduction Reactions of Metal Ions in Polyelectrolyte Films

We fabricated slippery liquid-immobilized coating (SLIC) films by reacting a slippery liquid (polymethylhydrosiloxane) near the surface of a polyelectrolyte film containing silver ions prepared by the layer-by-layer method. The obtained films maintained their slipperiness after chemical and physical treatments, in contrast to slippery liquid-infused porous surfaces. The high chemical and physical stabilities of the films were attributable to gelation and immobilization of the lubricant owing to an oxidation-reduction reaction with subsequent dehydration condensation of Si-OH on the outer surface of the polyelectrolyte film and the bonding of Si-H with NH2 groups within the polyelectrolyte film, respectively. Moreover, the SLIC films exhibited a high degree of slipperiness with respect to low-surface-tension liquids. To the best of our knowledge, this technique of lubricant immobilization using silver ions has not been reported previously. The films should be suitable for use in various applications where contamination must be prevented under extreme conditions, such as those requiring high physical durability and organic solvent use.

Porous Transition of Polyelectrolyte Film through Reaction-Induced Phase Separation Caused by Interaction with Specific Metal Ions.

We describe a novel method for the simple and eco-friendly fabrication of porous polyelectrolyte films. A polyelectrolyte with many amine groups undergoes structural transformation from a dense to a porous structure upon immersion in a specific metal ion solution. The porous transition was the result of a reaction-induced phase separation, which was caused by the formation of new bonds between the polyelectrolyte and metal ions. This method enables control of the pore size of the porous structure in the nanoscale (54 nm) to microscale (1.63 μm) range through variation of the concentration or type of metal ions in the solution. To the best of our knowledge, this is the first report illustrating wide-range control of the pore size of a porous polyelectrolyte structure achieved by metal ions. These porous polyelectrolyte films with adjustable pore size and metastable metal ions can be employed in applications such as adsorption and catalysis.