Journal of the Japan Society of Colour Material

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We report here on the manufacturing methods for emulsifier-free (EF-) oil-in-water (O/W) emulsions, in which oil and water were mechanically mixed in the absence of any emulsifiers such as surfactants. A commercially available bath-type ultrasonic cleaner (Bath-US; 42 kHz, 26 W) did not disperse dodecane (DD) completely in water even by the treatment for 15 min, and the average diameter of DD droplets in the EF-dodecane-in-water (DD/W) emulsions prepared was several micrometers. Using a commercially available horn-type ultrasonic homogenizer (Horn-US; 19.5 kHz, 600 W), the EF-DD/W emulsions were prepared by treatment for ~1 min, and the average diameter of DD droplets in EF-DD/W emulsions prepared was ~1 μm. Preparation of EF-DD/W emulsions using a high-powered bath-type ultrasonicator (HPBath-US; 28 kHz, 300 W) that we developed required the treatment period for ~1 min. The DD droplets in EF-DD/W emulsions prepared with HPBath-US became several hundred nanometers in diameter by treatment for ~10 min. The preparation of EF-DD/W emulsions with a commercially available rotor-stator homogenizer (RS-HG; 15,000 rpm, 800 W) required the treatment period for ~1 min, and DD droplets in DD/W emulsions prepared were several micrometers in diameter. Colloidal stability of EF-DD/W emulsions prepared with Horn-US and HPBath-US was higher than that of EF-DD/W emulsions prepared with Bath-US and RS-HG. These studies indicate that HPBath-US has advantages for the manufacturing of EF-O/W emulsions. Furthermore, the continuous manufacturing of EF-DD/W emulsions was achieved by attaching the flow chamber with HPBath-US.

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Tunable colloidal photonic crystal films consisting of loosely packed colloidal crystals immobilized in elastomers were prepared. The prepared soft film was adhered to an aluminum specimen and the tensile testing was performed. Before applying the tensile force, the film exhibited red color due to Bragg reflection from (111) lattice planes of the face-centered cubic structure, which are parallel to the film surface. With increasing strain on the specimen, the Bragg wavelength of the colloidal crystals was blue-shifted, mainly owing to reduction of the lattice spacing. Consequently, the color of the film changed to orange, yellow, and green in accordance with increasing strain. The prepared films can be used as simple sensors that detect the strain on the materials to which they are adhered based on color change.

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