S051024 マイクロ流路流れでの障害物によるひも状ミセル水溶液の流動誘起構造変化([S051-02]複雑流体の流動現象(2))

Abstract

A surfactant, cetyltrimethylammonium bromide (CTAB) forms wormlike micelles in aqueous solutions with additive of sodium salicylate (NaSal). Wormlike micelles can self-organize under flow to form higher-order flow-induced structures (FISs). In this study, flow patterns and a FIS formation are investigated experimentally in the microchannel flow past obstructions. Test fluids used were entangled worm-like micelle solutions of CTAB and NaSal. Steady laminar flow patterns were observed in a water flow, where the flow can be considered as the Hele-Shaw flow. The Hele-Shaw flow pattern was altered drastically in a worm-like micelle solution (3mM, molar ratio 1:1), where the flow was no longer steady. The flow pattern change was accompanied by a formation of FIS in the worm-like micelle solution, which we observed directly with a phase-contrast microscopy. We observed sticky, viscous, transparent streaks of FIS in the fluid flowing down from the obstructions, where the apparent property of the fluid was locally changed. The streaks are having a refractive index different from that of surrounding fluid, but they were hardly observed with bright field images. The streaks were mostly observed in the stagnation flow behind each obstructions as well as the entry flow into the gap between obstructions. The flow with the streaks was heterogeneous and highly unsteady. The fluctuations of the streaks were observed downstream of the obstructions, where the difference in flow velocity across the streak plays a crucial role in the deformation of the streak.