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Yukikazu Takeoka

Publications and source records attributed to Yukikazu Takeoka.

6 recordsLinked to original sources
PubMed2006

Visualizing conformations of subchains by creating optical wavelength-sized periodically ordered structure in hydrogel.

Thick single-crystalline fcc colloidal crystals exhibiting structural color are obtained by a solvent evaporation method from silica colloidal particle suspensions. A periodically ordered interconnecting porous structure can be imprinted in thermosensitive N-isopropylacrylamide (NIPA) gels by using the colloidal crystals as templates. The porous structure endows a structural color to the NIPA gels. We find that the peak position of the reflection spectra from the porous gels (lamdamax') is expressed as a function of the swelling degree and is synchronized with the change in the swelling degree. The color can be precisely tuned by simply changing the amount of the monomer and the cross-linker in the pre-gel solutions. We can estimate the linear expansion factor (> or =1) of the subchains by comparing the peak position at a given situation (lamdamax') and the reference state (lamdamax,0'), in which the subchains behave as Gaussian coils. Creating the periodically ordered structure, which is similar in size to the wavelength of optical light, in the gels allows us to determine the behavior of polymer chains by observing the structural color.

Journal Article↗
PubMed2006

Preparations and optical properties of ordered arrays of submicron gel particles: interconnected state and trapped state.

Two types of thermosensitive opal-structured hydrogel systems, "interconnected" and "trapped" gel particle arrays, were newly developed by extremely simple methods using silica colloidal crystal as a template. Although both systems diffract visible light following Bragg's law combined with Snell's law, the temperature dependences of their optical properties were quite different. The "interconnected" array exhibited a reversible change in the peak values of the reflection spectra, mainly determined by the swelling ratio of the hydrogel, as a function of the water temperature. Since the swelling ratio is dominant over the peak value, we can observe water temperature through the color of the interconnected type of gel membrane. The "trapped" array revealed a reversible change in the peak intensity of the reflection spectra with the change in temperature, whereas no change in the peak position was observed. We can interpret this phenomenon in the following ways. As the rise in temperature causes a decrease in the water content of the NIPA gel particles, the gel particles becomes stickier on the cavity wall of polystyrene PPM. This may induce a disturbance in the ordered array of the gel particles and form many layers of rough surfaces in the inverse opal structure of the PPM. This situation may lead to the stronger diffused reflection of light from the gel particles, resulting in the decrease in peak intensity at higher temperatures.

Journal Article↗
PubMed2004

Surface activity and redox behavior of a non-ionic surfactant containing a phenothiazine group.

A novel non-ionic surfactant, alpha-(phenothiazinylhexyl)-omega-hydroxy-oligo(ethylene oxide) (PCPEG) containing phenothiazine as an electro-active group has been synthesized. Fundamental interfacial behavior of the surfactant at the air/water interface has been investigated by means of surface tensiometry to provide an insight into the relationship between the structure of the hydrophobic moiety and the surfactant properties. A comparison of diffusivity of PCPEG in the aqueous phase with that in the acetonitrile solution at high PCPEG concentrations shows that micellization has a pronounced effect on the redox behavior of PCPEG. The electrochemical responses for PCPEG aqueous solutions at the interface of a glassy carbon electrode are fairly dependent on the concentration of PCPEG. Above CMC, PCPEG molecules self-associate to form micellar aggregates and the formation and disruption of micelles can be reversibly controlled by change in the redox state of the phenothiazine group. The cyclic voltammetric responses for PCPEG aqueous solutions have been correlated with the dissolved states to explain the distinctive feature of the surfactant.

Adsorption↗
PubMed2003

Self-sustaining peristaltic motion on the surface of a porous gel.

We report the structural color behavior of a periodic ordered mesoporous gel synchronized with the Belousov-Zhabotinsky (BZ) reaction. The structural colored concentric rings which were spatiotemporally spread out on the porous gel were observed during the BZ reaction. The color tone of the structural color, which is determined by the swelling ratio of the gel, was periodically changed. This is the first evidence that a self-sustaining peristaltic motion occurs on the surface of a gel.

Journal Article↗