2016 Fiscal Year Annual Research Report
| Project/Area Number |
15F15769
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| Research Institution | The University of Tokyo |
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Principal Investigator |
田中 肇 東京大学, 生産技術研究所, 教授 (60159019)
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| Co-Investigator(Kenkyū-buntansha) |
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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| Project Period (FY) |
2015-11-09 – 2018-03-31
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| Keywords | Hydrodynamics / Colloids / Viscoelasticity / Optical tweezers / Rheology |
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| Outline of Annual Research Achievements |
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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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
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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| Strategy for Future Research Activity |
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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Research Products
(3 results)
