Study on flow-indueed structure and instability of surfactant aqueous solution by measuring microscopic distribution of flow birefringence

2004 Fiscal Year Final Research Report Summary

• Project/Area Number: 15560133
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Fluid engineering
• Research Institution: Nagaoka University of Technology
• Principal Investigator: TAKAHASHI Tsutomu Nagaoka University of Technology, Faculty of Engineering, Associate Professor, 工学部, 助教授 (20216732)
• Project Period (FY): 2003 – 2004
• Keywords: surfactant aqueous solution / shear-induced structure / flow birefringence / micelles structure / flow instability / wormlike micelles

Research Abstract

This research is an investigation of flow property of surfactant aqueous to use as working fluid. We introduced a microscopic point of view into this research with considering the flow-induced structure change of micelles. Prof.Shikata, Osaka University, reported that the wormlike micelles are not only entangled but they are passing through each other. Since we thought that the micelles aligned stronger than polymer filaments by this concept, we measured the state of alignment of micelles by flow birefringence. Moreover, we aimed to develop the birefringence distribution microscope metrology that was able to measure the distribution of the flow birefringence from several μm at tens of μm intervals, and to measure the process from the change in the micelle that formed the texture structure such as banding to the generation of unstable flow by the resolution of the optical microscope order. The flow behavior of a surfactant solution, CTAB/NaSal, in parallel plates flow cell which has 0.5 mm to 2.0mm in gap was observed by using optical microscope. To make start-up flow with a constant flow rate, a syringe pump was used. It was observed by the flow visualization that all sample in the flow cell becomes opaque immediately after beginning of flow when the flow rate exceeds a certain value. In this case, the shear stress and strain applied homogeneously to the sample in the flow cell and then the shear induced two opaque thin layers formed near the upper and lower plates. After a while, a white band area which is orthogonal to the flow direction is formed on the entrance region. This band area is also the micelle's structure change but it is generated by elongation deformation in reservoir. The nonuniformity of this band area causes instability of flow. The instrument which can measure the flow birefringence at different 16 positions simultaneously was completed. By using this instrument, the start-up behavior of the distribution of the flow birefringence in the flow cell was measured.