| Project/Area Number |
17560158
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Fluid engineering
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| Research Institution | Osaka Prefecture University |
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Principal Investigator |
TAKAHIRA Hiroyuki Osaka Prefecture Univ., Graduate School of Engineering, Professor, 工学研究科, 教授 (80206870)
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| Project Period (FY) |
2005 – 2006
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| Project Status |
Completed (Fiscal Year 2006)
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| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2006: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 2005: ¥2,500,000 (Direct Cost: ¥2,500,000)
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| Keywords | Microbubble / Surfactant / Surface Tension / Adsorption / Desorption / Permeation Resistance / Deformation / Multilayers / Equilibrium Radius |
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| Research Abstract |
The shrinkage and growth of microbubbles that were trapped with laser-trapping technique or attached underneath a cover glass were observed with a CCD camera. The influence of gas diffusion was investigated for two kinds of surfactant microbubbles; one was Levovist and the other was Imavist. Two kinds of equilibrium radii were observed for laser-trapped shrinking microbubbles. The first one was related to the equilibrium surface concentration of surfactant. The other was related to the decrease of the surface tension due to the compression of the surface area at the maximum surfactant concentration. It was shown that when the ambient liquid pressure increased, a tiny microbubble shrank accompanied with large surface deformation, and did not return to the initial size even after the pressure was reduced. On the other hand, a large microbubble shrank nearly spherically. The depression of bubble surface suggests the formation of multilayers of surfactant or lipid on bubble surface. It was also shown that air diffusion enhanced the growth of the Imavist.
A bubble model was also constructed by considering the adsorption/desorption of surfactant, the dynamic surface tension, and the gas permeation resistance of surfactant or lipid layers. The profiles of laser-trapped microbubbles were compared with simulations based on the model. The simulations with the dynamic surface tension agreed with the experimental results. The simulations showed that the rate of adsorption of surfactant was much faster than the shrinking speed of microbubbles. The decrease of surface tension due to the decrease of the surface area of a microbubble was a significant factor to determine the bubble profile. The simulations considering the gas permeation resistance were in good agreement with the experiments for nearly spherical bubbles attached to the cover glass. The results also showed that the increase of the permeation resistance during bubble shrinkage stabilized microbubbles.
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