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It is known that the CTAB/NaSal aqueous solution forms wormlike micelles when the concentration is higher than a certain value and shows the flow-induced structure change when both the shear rate and shear strain exceed respective critical values. In the present work, the start-up behavior of this surfactant solution in a two-dimensional abrupt contraction channel driven by a constant pressure was investigated. At a low driving pressure, the flow rate increases gradually and reaches an equilibrium state. When the driving pressure is higher than a certain value, the flow rate rises at a certain elapsed time. The elapsed time showing increase in flow rate shortens with increasing driving pressure. In the entry area of the narrow channel, a pair of wedge shape opaque regions appears. From the comparison with the observation in Couette flow of the same solution, it is found the opaque regions are caused by shear induced structure and the viscosity of the regions is higher than the other region. The regions grow up and make the other region with low viscosity narrower. The opaque regions suddenly break and disappear when the flow rate changes. Flow instability is induced by a sudden change of flow states. These phenomena are characteristic of the fluid showing the flow-induced structure change, whereas ordinary polymer solution do not exhibit such behavior.

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Optically transparent and stable sols of copper ion doped zinc sulfide (ZnS:Cu) nanoparticles were obtained by heating a mixture of ethylene glycol aqueous solution and sulfide precipitate at 348 K for 24 h. The sulfide precipitates containing zinc ions, copper ions and citrate ions were peptized in an aqueous solution of ethylene glycol having a 0.5 molar fraction of [Ethylene glycol]/ ([H 2 O]+[Ethylene glycol]). Photoluminescence characteristics and stability of the sols depended on the amount of citrate ions in the aqueous solution which was used for preparing sulfide precipitates. The citrate ions strongly affected the characteristics of the obtained sols with dispersion of the copper ion doped-ZnS nanoparticles. According to TGDTA curves and N 2 adsorption isotherms of the precipitated sulfides, the citrate ions in the aqueous solution containing zinc ions, copper ions coprecipitated in the sulfide precipitates formed by adding the sodium sulfide aq. The citrate ions played an important role for the peptization and the formation of stable sols.

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