Particles transport driven by a temperature gradient in a solution is known as thermophoresis or Soret effect. The drift velocity $v T$ of a particle is expressed as $v T = − D T ∇ T$ , where $D T$ is a thermophoretic mobility. Therefore, the thermophoretic mobility is a parameter to characterise the nature of thermophoresis, and the systematic measurement of $D T$ for various combinations of particles and solvents is necessary for its potential application. In the present work, we develop the microfluidic system called microgap Soret cell and show its validity by obtaining $D T$ for wide experimental conditions. It is shown that the microgap Soret cell can rapidly and directly obtain the thermophoretic mobility of a particle with the diameter of $O ( 1 ) μ m$ by maintaining the large temperature gradient in the microfluidic system. Moreover, by using the microgap Soret cell, the temperature dependency of $D T$ is investigated for thermophoresis of polystyrene particles in solutions of sodium hydroxide, polyethylene glycol, and glycerol.

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Direct observations of thermophoresis in microfluidic systems

References

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