Direct observations of thermophoresis in microfluidic systems

Abstract

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) mm 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.

Flow with nanoparticle clustering controlled by optical forces in quartz glass nanoslits

“…With the aid of such a restriction, we can stably trap the target particles without pushing them away. In addition, the nanoslit confinement can diminish unwanted thermal and fluid phenomena, such as thermal convection and thermophoresis in microfluidic systems (Tsuji et al 2017. Therefore, the proposed device in the present study is a suitable starting point for investigating the optical manipulation in the nanofluidic devices and developing novel particle flow control techniques.…”

Microfluidic Pump Driven by Anisotropic Phoresis

“…Catalytic surfaces and related chemical gradients have shown a large potential in microfluidic applications [29][30][31][32], while thermal gradients are relatively less exploited. Thermal gradient-driven motion has though promising prospectives since it works equally well in charged and neutral solutions, and it is pollution-free due to the absence of surfactants or chemical fuels, which enables the way to bio-compatible applications [33][34][35]. Furthermore, thermal gradient-driven motion allows optical microscale operations with optical heating which is the basic principle of the emerging field of optofluidics [36,37].…”

Negative Thermophoretic Force in the Strong Coupling Regime

“…In the limit of vanishing coupling, the oscillator's frequency ω is not affected by the heat bath's temperature, the rightmost term in (15) vanishes, and the usual energy expression for a harmonic oscillator is recovered. However, in the strong coupling regime, the spectrum frequency ω is affected by the energy of the oscillators around it, i.e.…”

“…As a cautionary note, the reader is warned that, in the literature, the terms thermodiffusion and thermophoresis are sometimes used interchangeably (see e.g. [1,2,15,16]). However, while the former (also known as Soret effect, or Ludwig-Soret effect) refers to the formation of a concentration gradient as a result of a thermal gradient, the latter refers to the migration of a particle in a fluid due to the presence of a temperature gradient [17].…”

“…This physical behavior may be modeled as ω(T ) = ω 0 e −αT (with a positive coupling constant α). The resulting energy function (15) displays one (and only one) minimum at a positive temperature T = T * . This temperature is known as the reversal temperature [5], i.e.…”