Decomposition of Mullite by Silica Volatilization

Thermal decomposition of mullite into corundum was investigated using a high-temperature X-ray single-crystal camera equipped with a gas-flame furnace and by scanning electron microscopy and electron probe microanalysis (EPMA). When heated to ∼1750°C, mullite decomposed to corundum by the liberation of the SiO₂ component with topotaxial relations of:

• (1) 

  (310)_mull∥(001)_cor; [001]_mull∥[110]_cor
• (2) 

  (130)_mull∥(001)_cor; [001]_mull∥[110]_cor
• (3) 

  (110)_mull∥(001)_cor; [001]_mull∥[110]_cor

Thus, it was considered that, when mullite decomposed into corundum, their oxygen close-packed planes were almost preserved. The SEM photographs showed that the crystals of the developed corundum are prismatic and ∼5 μm wide. The EPMA showed that the phase boundary between mullite and developed corundum is discontinuous.     

Preparation and optical properties of an all‐polymer light modulator using colored N‐isopropylacrylamide gel particles in a gel‐in‐gel system

A novel all‐polymer light modulator with a gel‐in‐gel system was developed. The gel‐in‐gel system was constructed with colored gel particles responsive to stimuli held independently in another stimuli‐nonresponsive gel matrix. Well‐known thermoresponsive N‐isopropylacrylamide (NIPAM) gel particles containing a pigment were dispersed and fixed in an outer stimuli‐nonresponsive gel matrix. When poly(vinyl alcohol)–styrylpyridinium (PVA–SbQ) was used for the outer gel matrix, the light modulator showed excellent color‐changing properties because the PVA–SbQ matrix was selectively formed around the NIPAM gel particles and the particles exhibited a large volume change in the matrix. The temperature when the outer gel matrix was formed affected the haze of the light modulator. When the outer gel matrix was formed in the swollen state of the NIPAM gels, the haze of a light modulator increased with heating. On the contrary, the haze of a light modulator prepared in the shrunken state of the NIPAM gels decreased with heating. The response time of the color change was less than 1 s. The gel‐in‐gel system made a very fast macroscopic color change, taking advantage of the fast response of the micrometer‐sized gel particles. We believe that a light modulator with a gel‐in‐gel system may find various applications in optical devices. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2295–2303, 2007     

Study on shock wave and turbulent boundary layer interactions in a square duct at Mach 2 and 4

In this paper, the outline of the Mach 4 supersonic wind tunnel for the investigation of the supersonic internal flows in ducts was firstly described. Secondly, the location, structure and characteristics of the Mach 2 and Mach 4 pseudo-shock waves in a square duct were investigated by color schlieren photographs and duct wall pressure fluctuation measurements. Finally, the wall shear stress distributions on the side, top and bottom walls of the square duct with the Mach 4 pseudo-shock wave were investigated qualitatively by the shear stress-sensitive liquid crystal visualization method. The side wall boundary layer separation region under the first shock is narrow near the top wall, while the side wall boundary layer separation region under the first shock is very wide near the bottom wall.     

Controlling optical properties of a novel light‐modulation device consisting of colored N‐isopropylacrylamide gel particles dispersed in a poly(vinyl alcohol) solution

The optical properties of a novel light modulator consisting of colored particles of N‐isopropylacrylamide (NIPAM) gel, a well‐known thermoresponsive gel, dispersed in an aqueous poly(vinyl alcohol) solution were examined. The performance of the light modulator was mainly defined by two factors: the NIPAM gel properties and device compositions. The NIPAM gel properties included the amount of the volume change, the volume‐change temperature, and the pigment concentration in the NIPAM gels. The larger the volume change was of the NIPAM gel particles, the wider the transmittance change became. The color‐change temperature was controlled by the manipulation of the volume‐change temperature of the NIPAM gels with the addition of sodium dodecyl sulfate (SDS). The volume‐change temperature of the NIPAM gels became higher with an increasing concentration of SDS. The pigment concentration also had a significant effect. The higher the pigment concentration was in the NIPAM gels, the wider the breadth of the transmittance changes became. This occurred because, in the case of low pigment concentrations, absorbed water diluted the pigment, and this led to low absorption at each NIPAM gel particle. The properties of light modulation could also be controlled by the composition of the light‐modulation layer. The two main parameters were the concentration of the gel particles in the layer and the thickness of the layer. The transmittance of the light modulators decreased as the thickness and/or concentration of the gel particles increased. Light modulators with various colors were obtained with NIPAM gel particles containing pigments of different colors. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 362–368, 2006     

Photo‐patterning of smart light‐modulation gel

A novel method for fabricating desired patterns of smart light‐modulation gels, which consist of thermoresponsive N‐isopropylacrylamide (NIPAM) gel particles containing pigment, was developed. The patterns were fabricated by photo‐patterning of dispersion of colored NIPAM gel particles in photosensitive poly(vinylalcohol)‐styrylpyridinium solution. The pattern showed drastic color changes in response to the surrounding temperature changes. By repeated cycles of the patterning method, several independent patterns that contained different color particles were fabricated. In addition, a thermosensor array was also fabricated, which was constructed with independent patterns containing colored NIPAM gel having different color‐changing temperatures. The patterning method studied here is considered to have strong potential to extend the application field of the smart light‐modulation gels. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5351–5357, 2006