Hirohmi Watanabe

Preparation of low-surface-energy poly[2-(perfluorooctyl)ethyl acrylate] microparticles and its application to liquid marble formation.

We demonstrate the successful preparation of stable liquid marbles from various liquids. This is accomplished by using low-surface-energy poly[2-(perfluorooctyl)ethyl acrylate] (PFA-C(8)) as microparticles. The PFA-C(8) microparticles were prepared by the spontaneous self-organized microparticulation of PFA-C(8). The physical properties remained intact in the polymer morphology as confirmed by wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) measurements. The extremely low surface energy of PFA-C(8) provides a high solid-liquid spreading coefficient (S(S/L)) value for various combinations of liquids. As a result, liquid marbles were obtained from various liquids, unlike the case with other fluorine polymer particles such as poly(tetrafluoroethylene) (PTFE) and poly(vinilydene fluoride) (PVDF). These results suggest that the technique is widely applicable for preparing novel functional materials.

Robust Liquid Marbles Stabilized with Surface-Modified Halloysite Nanotubes

We have demonstrated the fabrication of fluorine-free liquid marbles from halloysite nanotube. Halloysite is a naturally occurring inorganic nanotube that has a high aspect ratio, and the surface was modified with octadecyltrimethoxysilane. The surface-modified halloysite formed pincushion agglomerates on the surface of the liquid droplets, which create superhydrophobic surface similar to that of the plant gall surface prepared by aphids. As a result, the liquid marbles showed high mechanical strength upon impact without the use of low surface energy fluoroalkyl or fluorine-modified materials. Our results suggest a new strategy for designing novel materials for liquid marbles inspired by nature.

Preparation of poly(lactic-acid)-particle stabilized liquid marble and the improvement of its stability by uniform shell formation through solvent vapor exposure

A liquid marble was prepared from bio-based poly(lactic acid) [PLA] microparticles and water droplets. Solvent vapor exposure to the liquid marble changed the morphology of the granular PLA microparticle shell layer to a film-like shell layer even though the spherical shape of the liquid marble is retained. The morphological changes suppressed the evaporation of the water within the liquid marble by a factor of six compared with a liquid marble without the solvent vapor treatment. The compression test revealed that the mechanical stability of the solvent-treated liquid marble was changed due to the increased rigidity of the shell structure. Solvent vapor exposure is a simple but effective way to fabricate a robust liquid marble with long-term stability.

Manipulation of surface properties: the use of nanomembrane as a nanometre-thick decal

Precise control of surfaces and interfaces is essential for the fabrication of various functional materials. Although various methods have been applied to the functionalization of surfaces, these methods are specialized for the fabrication of specific surfaces for specific purpose. In this context, a versatile, yet efficient tool for the surface manipulation is strongly desired. Here, we demonstrate a simple method of functionalizing various surfaces through a decal-like transfer of a giant nanomembrane. Control of wettability was chosen as an example, and a hydrophobic nanomembrane was transferred to various other substrates, including Si, polymer film, and metal. A drastic change in contact angle clearly indicated that the wettability of the processed material was identical to that of the surface-functionalized nanomembrane. In contrast, other physical properties such as the mechanical properties of the processed material remain unchanged. The decal-like transfer of nanomembrane will become a powerful means for the fabrication of unique functional surfaces.

Biobased Polymer Coating Using Catechol Derivative Urushiol

We have investigated the mechanism of the superior mechanical robustness of coated thin films of the catechol derivative urushiol. We synthesized hydrogenated urushiol (h-urushiol) by hydrogenating the double bonds in the long alkyl side chain of urushiol, and the physical properties of thin films of mixtures of urushiol and h-urushiol were evaluated. Atomic force microscopy observations revealed that these coated thin films have a homogeneous surface with no phase separation, regardless of the h-urushiol content, arising from the similarity of the chemical structures. The films showed good adhesive properties because the adhesion originates from the catechol structure. In contrast, curing time depended strongly upon the h-urushiol content. The curing of the h-urushiol thin film took 12 h, whereas the urushiol thin film was cured within 10 min. Moreover, the strain-induced elastic buckling instability for mechanical measurements test and the bulge test confirmed that the increase in the h-urushiol content decreased the mechanical strength. Because the double bonds in the urushiol side chain contribute to forming the highly cross-linked structure, the lack of double bonds in h-urushiol resulted in the slow curing and low mechanical strength. Interestingly, the mechanical robustness started to increase over 80 mol % h-urushiol. The saturated long alkyl side chain of h-urushiol faced the surface, and the regular structure of the uniform side chain may improve the mechanical properties of the coated film. Our results will help to develop biomimetic catechol-based coatings.

Concealing surface topography by attachment of nanometer-thick film.

Concealing of surface topology of substrates by decal-like attachment of nanomembrane is demonstrated. The nanomembrane attachment provides a flat surface on various substrates, including porous substrates, and the surface property such as wettability was changed to that of the nanomembrane. The monitoring of drying process revealed that a nanomembrane with certain thickness tolerates their flexural deflection during the procedure. Moreover, the supporting position of nanomembranes as well as the physical properties of nanomembranes strongly affected the degree of deflection. The decal-like attachment of nanomembranes shown here is potentially a powerful method for creating a new functional surface that is independent of the topological and chemical properties of the original substrate.

One-step nanopatterning of conjugated polymers by electron-beam-assisted electropolymerization

We propose a one-step nanopatterning method where liquid monomers are polymerized directly with an electron beam under an atmospheric pressure. The method allows precise positional control of an electron beam that induces electropolymerization based on an anodic oxidation only in the irradiated areas. Various versatile conjugated polymers, including polypyrrole, polyaniline and poly(3-hexylthiophene), have been directly polymerized from monomers without solvents and patterned by our one-step nanopatterning method. Vertically oriented arrays of nanorods several hundred nanometers in diameter with an aspect ratio (height to diameter) of around two were fabricated.