2001 Fiscal Year Final Research Report Summary
Effects of Shear Flow on Structures of Molecular Self-Assembly
| Project/Area Number |
11440207
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
機能・物性・材料
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| Research Institution | Tokyo Metropolitan University |
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Principal Investigator |
KATO Tadashi Tokyo Metropolitan University, Science, Professor, 理学研究科, 教授 (30142003)
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| Project Period (FY) |
1999 – 2000
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| Keywords | shear flow / neutron scattering / light scattering / surfactant / liquid crystal phase / lamellar phase / X-ray scattering / molecular self-assembly |
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| Research Abstract |
Surfactant molecules form aggregates (called micelles) in water. When the surfactant concentration exceeds a specific value, these aggregates associate into higher-order structures such as lyotropic liquid crystal phases. As the length scale of these molecular self-assemblies is much longer than the molecular size, weak perturbations induce large change in their structures. In the present study, effects of shear flow on the structures of lamellar phase formed by nonionic surfactant C_16H_33(OC_2H_4)_7OH and water has been discussed based on the data obtained by using scattering techniques.
First, small-angle x-ray scattering (SAXS) has been measured in the wide concentration and temperature range to investigate fine structures of the lamellar phase at rest. By analyzing both the position and line shape of the diffraction peak, it has been found that bilayers forming lamella phase have defects like holes and that these defects suppress the undulation of bilayers.
Then small-angle neutron scattering has been measured under shear flow in the range of shear rate 10^<-3>-10^2s^<-1>, much lower than those for other studies reported so far. Diffraction peaks have been observed in flow, gradient, and vorticity directions. It has been found that the lamellar spacing (d) decreases substantially (about 30 %) at the shear rate around 1 s^<-1>. With the further increase in the shear rate, d increase slightly and leveled off. Interestingly, the d value under shear does not depend on the concentration very much. Taking into account the results of line shape analyses of SAXS, it has been elucidated that the water layer between bilayers is excluded by shear flow, suggesting the separation into two phases with different concentrations.
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