Separation of Nano- and Microparticle Flows Using Thermophoresis in Branched Microfluidic Channels

Abstract

Particle flow separation is a useful technique in lab-on-a-chip applications to selectively transport dispersed phases to a desired branch in microfluidic devices. The present study aims to demonstrate both nano- and microparticle flow separation using microscale thermophoresis at a Y-shaped branch in microfluidic channels. Microscale thermophoresis is the transport of tiny particles induced by a temperature gradient in fluids where the temperature variation is localized in the region of micrometer order. Localized temperature increases near the branch are achieved using the Joule heat from a thin-film micro electrode embedded in the bottom wall of the microfluidic channel. The inlet flow of the particle dispersion is divided into two outlet flows which are controlled to possess the same flow rates at the symmetric branches. The particle flow into one of the outlets is blocked by microscale thermophoresis since the particles are repelled from the hot region in the experimental conditions used here. As a result, only the solvent at one of outlets and the residual particle dispersion at the other outlet are obtained, i.e., the separation of particles flows is achieved. A simple model to explain the dynamic behavior of the nanoparticle distribution near the electrode is proposed, and a qualitative agreement with the experimental results is obtained. The proposed method can be easily combined with standard microfluidic devices and is expected to facilitate the development of novel particle separation and filtration technologies.

Progress of Microfluidic Continuous Separation Techniques for Micro-/Nanoscale Bioparticles

“…Temperature is a fundamental variable in many fluidic experiments and plays an important role in determining particle transport ability in a fluid as described by the total mass flux equation below: where D is the Brownian diffusion coefficient, c i is concentration of species i , and D T and T are thermal diffusivity and temperature, respectively. There has been active research on thermophoresis, which controls mass transfer and particle motion by forming a microthermal environment (i.e., thermal gradient) in microfluidic devices [ 100 , 101 , 102 , 103 , 104 , 105 , 106 ]. This is because temperature is a variable that has a large influence on the kinetic properties of particles and solvents, including viscosity, which provides an advantage in terms of sensitivity compared to standard particle manipulation.…”

“…As shown in Figure 3 A(i), a thin film electrode heater was integrated in the Y-shaped microfluidic channel to induce a temperature increase, which maintained the boundary condition of uniform heat flux by applying a DC power source [ 101 ]. In addition, a continuous fluid flow using a small pressure difference (0.5 or 1.0 Pa) acts as a heat sink, creating a thermal gradient for thermophoresis of the particles.…”

“…Particles separated toward outlet α or β according to their thermophoretic responses. Reprinted with permission from MDPI [ 101 ]; ( B ) ( i ) Illustration to describe creation of gas (CO 2 ) concentration gradient using air-permeable PDMS microchannel. ( ii ) Separation results using gas concentration gradient.…”

A Review on Optoelectrokinetics-Based Manipulation and Fabrication of Micro/Nanomaterials

“…To address real-world needs for manipulation and fabrication of micro/nanomaterials, a number of micro-/nano-scaled methods have been presented. Typical examples include microfluidic [14,15], acoustic [16,17], electrokinetics [18,19], magnetic [20,21], optical [22,23], thermal [24,25], and atomic force microscope [26,27] approaches. An emerging topic on the manipulation and fabrication of micro/nanoparticles is about how to develop a novel mechanism that can complement what a single technique can offer.…”

Editorial for the Special Issue of Selected Papers from the 9th Symposium on Micro-Nano Science and Technology on Micromachines

“…This Special Issue covers these topics with five papers. First, separation of nano- and micro-particle flows in branched microfluidic channels using thermophoresis [10]. Localized temperature increases near the branch are achieved using the Joule heat from a thin-film micro electrode embedded in the bottom wall of the microfluidic channel.…”