A fast and highly controllable method of fabricating large films of photonic crystals of colloids is reported. A charge‐stabilized colloidal suspension was run in a flat capillary driven by a pressure‐regulated air pulse. The colloidal crystal texture formed in the capillary was a sensitive function of air pressure. Above a critical pressure, the entire capillary was filled with a uniform single‐domain texture whose transmittance spectrum showed a high quality as a photonic crystal, i.e., excellent opacity at a photonic bandgap and high transparency at other wavelengths. The present method is easily applicable to industrial processes for mass production.
Dilute charged colloidal silica (particle diameter = 110 nm) containing pyridine exhibits a novel directed crystallization under a temperature gradient. The crystal growth can be explained in terms of a combination of heat conduction and thermally induced crystallization. Well-oriented and large (1 mm × 10 mm × ∼30 mm) single-domain crystals are formed in a short time (<10 min). Moreover, they have sharp and deep transmission dips as well as good spatial uniformity in the Bragg wavelength (∼0.1%).
Colloidal crystals are potentially mass-fabricative and the most accessible three-dimensional photonic crystals in the optical regime. We found that a centimeter-sized single-crystalline domain of a colloidal crystal, an ordered latex colloidal array, could be instantaneously tailored through a dynamic process, i.e., quenching nonequilibrium ordering in a concentrated suspension induced by a momentary shear-flow. The single crystal is obtained in an extremely simple manner in a tractable container with a fixed crystallographic orientation, and resulting samples are sufficiently stable against external disturbance for practical application. The proposed method will contribute to the evolution of photonic crystal research and applications.
Particle adhesion onto hydrogels has recently attracted considerable attention because of the potential biomedical applications of the resultant materials. A variety of interactions have been taken advantage of for adsorption, including electrostatic forces, hydrophobic interactions and hydrogen bonding. In this study, we report significant adsorption of submicron-sized silica particles onto hydrogel surfaces in water, purely by van der Waals (vdW) attraction. The vdW forces enabled strong adhesions between dielectric materials in air. However, because the Hamaker constant decreases in water typically by a factor of approximately 1/100, it is not clear whether vdW attraction is the major driving force in aqueous settings. We investigated the adsorption of silica particles (diameter = 25–600 nm) on poly(acrylamide) and poly(dimethylacrylamide) gels using optical microscopy, under conditions where chemical and electrostatic adsorption is negligible. The quantity of adsorbed particles decreased on decreasing the Hamaker constant by varying the refractive indices of the particles and medium (ethyleneglycol/water), indicating that the adsorption is because of the vdW forces. The adsorption isotherm was discussed based on the adhesive contact model in consideration of the deformation of the gel surface. The present findings will advance the elucidation and development of adsorption in various types of soft materials.
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