| 研究課題/領域番号 |
15F15769
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| 研究機関 | 東京大学 |
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研究代表者 |
田中 肇 東京大学, 生産技術研究所, 教授 (60159019)
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| 研究分担者 |
BRUOT NICOLAS 東京大学, 生産技術研究所, 外国人特別研究員
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| 研究期間 (年度) |
2015-11-09 – 2018-03-31
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| キーワード | Hydrodynamics / Colloids / Viscoelasticity / Optical tweezers / Rheology |
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| 研究実績の概要 |
Interactions between particles in colloidal systems are relevant to numerous problems. Systems of dilute colloids can be used as models of elements coupled through the hydrodynamic interaction in a low Reynold's number regime, which is useful to understand cell motility, particles sedimentation or the flowing of complex fluids in confined environments like blood cells in small veins, while dense suspensions that are used to model atomic systems have a phase diagram that relies on the details of the interactions.
Colloidal systems can also be subject to complex fluid-particle interactions such as in thermophoresis when imposing a temperature gradient, which can be used to control colloid concentration fields. This project aims at measuring hydrodynamic interactions between pair of colloids in complex fluids. In a new development, we are also investigating how heated colloids can be used to control colloid concentration fields.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
Optical tweezers are used to manipulate colloids in complex fluids. After making improvements mainly in the computer interface of the setup, hydrodynamic interactions between two colloidal particles have been measured. The study focused on colloids in shear-thinning aqueous solutions of polyethylene glycol. While it is known that the drag coefficient of a single particle decreases with its velocity in such solutions, we did not find any nonlinearity in the interaction between the two colloids.
We then moved to the question of drag coefficient of a colloidal probe in a bath of smaller colloids (that do not interact directly with the optical tweezers) and found a strong nonlinearity of the drag coefficient at low driving speeds. By adding confocal imaging to the setup, we were able to show that the origin of the effect is the formation of aggregates of colloids around the probes because of their heating by the laser from the optical tweezers.
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| 今後の研究の推進方策 |
The aggregates formed by the thermophoretic motion of colloids around probes provide a new technique for the manipulation of colloids. Compared to other methods based on thermophoresis, the use of heated probes allows creating clusters of particles in the bulk of dense systems and controlling concentration fields very locally, which has potential applications in microfluidics and in studying nucleation processes in colloidal systems.
In the remaining six months, we plan to characterize the growth of aggregates and their strength against a flow in order to provide a functional platform for concentration fields manipulation.
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