Concentration-adjustable micromixer using droplet injection into a microchannel

A novel micromixing technique that exploit a thrust of droplets into the mixing interface is developed. The technique enhances the mixing by injecting immiscible droplets in a mixing channel and the methodology enables a control of the mixing level simply by changing the droplet injection frequency. We experimentally characterize the mixing performance with various droplet injection frequencies, channel geometries, and diffusion coefficients. Consequently, it is revealed that the mixing level increases with the injection frequency, the droplet-diameter-to-channel-width ratio, and the diffusion coefficient. Moreover, the mixing level is found to be a linear function of the droplet volume fraction in the mixing section. The results suggest that the developed technique can produce a large amount of sample solution whose concentration is arbitrary and precisely controllable with a simple and stable operation.Comment: 12 + 3 pages, 6 + 4 figure

Lubrication effects on droplet manipulation by electrowetting-on-dielectric (EWOD)

Electrowetting has a potential to realize stand-alone point-of-care (POC) devices. Here we report droplet-migration characteristics on oil-infused electrowetting-on-dielectric (EWOD) substrates. We prepare sparse micropillars to retain the oil layer in order to exploit the layer as a lubricating film. A physical model of the droplet velocity is developed, and effects of the lubrication, the oil viscosity, the droplet volume, and the thickness of solid and liquid dielectric layers are discussed. It is found that the droplet velocity is scaled as square of E, which differs from a relationship of cube of E for droplets sliding down on liquid-infused surfaces by gravity. Furthermore, our device achieves droplet velocity of 1 mm/s at the applied voltage of 15 V. The velocity is approximately tenfold as high as the same condition (applied voltage and oil viscosity) on porous-structure-based liquid-infused surfaces. The achieved high velocity is explained by a lubrication-flow effect.Comment: 16 pages, 10 figure

ICNMM2008-62207 LOCAL MICROFLOW CONTROL USING PHOTOTHERMAL VISCOSITY DISTRIBUTION

ABSTRACT A novel method of microflow control by locally heated liquid using an optical technique is described in this paper. Microflow control in the present study utilizes temperature dependence of the fluid property which becomes dominant in microscale. Since it is known that viscosity has strong temperature dependence, a local viscosity distribution has a potential to change microflow behavior. The purpose of the present study is to validate this concept of microflow control by using the local distribution of viscosity. In order to induce the temperature variation, photothermal effect is utilized

Particle sorting by optical radiation pressure with low energy density

This paper presents the development of a microfluidic device for particle sorting using optical radiation pressure with low energy density. The need for efficient particle manipulation in the microchannel has led to the recent development of a couple of advanced techniques of particle manipulation. An optical approach to sort particles in a microchannel by the optical radiation pressure can provide non-contact and remote handling technique of manipulating the particles. We utilized a two-dimensionally focused laser beam, namely light sheet, for a light source to enable the optical-based particle sorting with low energy density leading less damage to the sample and device. A microfluidic device in this study consisted of the channel structure made of SU-8 between silicon substrate and PDMS lid. Since SU-8 has higher refractive index than other materials, the total reflection of the optical wave occurs to serve the channel walls as a waveguide leading the 2D focused laser beam with less scattering. Particle migration to the direction of light propagation was verified without any damage in the chip under an irradiation of a 2 W laser beam, which had enough strong power to damage the polymer chip using a spot, namely 3D focused beam. Reasonable agreement of our experimental results with theoretical prediction was also confirmed