• 한국정밀공학회지
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• 제31권1호
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• pp.91-96
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• 2014

We present a droplet-manipulation method using opto-thermal flows in oils. The flows are originated from Marangoni and buoyancy effects due to temperature gradient, generated by the adsorption of light on an amorphous silicon thin film. Using this method, we can transport, merge and mix droplets in an extremely simple system. Since the temperature rise during the operation is small, this method can be used for biological applications without the damage on cell viability.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2013년도 춘계학술대회 논문집
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• pp.571-572
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• 2013

• 한국가시화정보학회지
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• 제12권2호
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• pp.13-17
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• 2014

In the present study, the optofluidic droplet manipulation in a microfluidic platform was demonstrated via theoretical and experimental approaches. Optical scattering force and gradient force were used to separate and trap droplets. Two types of droplets were generated by a T-junction method in the microfluidic channel. While they approach a test region where the optical beam illuminates the droplets, they were pushed by the optical scattering beam. The displacement by the laser beam is dependent on the refractive index of the droplets. By using the optical gradient force, the droplets can be trapped and coalesced. In order to bring the droplets in a direct contact, the optical gradient force was used to trap the droplets. A theoretical modeling of the coalescence was derived by combining the optical force and drag force on the droplet.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.666-669
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• 2008

Droplet in miniaturized microfluidic systems have received much focused attention recently. In this work, electrical charging phenomenon of a conducting water droplet on the electrode under the dc electric field is studied and using this phenomenon droplet actuation method for microreactor applications is experimentally demonstrated. To find effects of key factors, the effects of electric field, medium viscosity, and droplet size are investigated. A scaling law of charging for the conducting droplet is derived from the experimental results. Unlike the case of a perfect conductor, the estimated amount of electrical charge ($Q_{est}$) of a water droplet is proportional to the 1.59 power of the droplet radius (R) and the 1.33 power of the electric field strength (E). (For a spherical perfect conductor, Q is proportional to R2 and E.) It is thought that the differences are mainly due to incomplete charging of a water droplet resulted from the combined effect of electrochemical reaction at electrode and the relatively low conductivity of water. Using this phenomenon, we demonstrate the transport of the charged droplet and fusion of two oppositely-charged droplets. When electric field is subjected sequentially on the electrode, the charged droplet is transported on the electrode. For the visualization of fusion of charged droplets, the precipitation reaction is used. When subjected to a DC voltage, two droplets charged are moving and merging toward each other due to the Coulombic force and chemical reaction is simultaneously occurred by coalescence of droplets. It may be due to the interchange effect of charge. It is shown that the droplet can be used for microreactor where transporting, merging etc. of reagents constitute unit operation.

• 한국가시화정보학회지
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• 제20권3호
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• pp.19-26
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• 2022

In droplet microfluidics, precise droplet manipulation is required in numerous applications. This study presents ultrasonic surface acoustic wave (USAW)-based microfluidic device for label-free droplet separation based on size. The proposed device is composed of a slanted-finger interdigital transducer on a piezoelectric substrate and a polydimethylsiloxane microchannel placed on the substrate. The microchannel is aligned in the cross-type configuration where the USAWs propagate in a perpendicular direction to the flow in the microchannel. When droplets are exposed to an acoustic field, they experience the USAW-induced acoustic radiation force (ARF), whose magnitude varies depending on the droplet size. We modeled the USAW-induced ARF based on ray acoustics and conducted a series of experiments to separate different-sized droplets. We found that the experimental results were in good agreement with the theoretical estimation. We believe that the proposed method will serve as a promising tool for size-based droplet separation in a label-free manner.

• 센서학회지
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• 제18권2호
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• pp.154-159
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• 2009

This paper describes two methods - stamp-to-stick bonding and microtransfer molding - to integrate microfluidic channel into an optoelectrofluidic device for in-channel microparticle manipulation. We have demonstrated the optoelectronic microparticle manipulation in the channel-integrated optoelectrofluidic device using a liquid crystal display. As injecting a liquid sample containing $15{\mu}m$-diameter polystyrene particles into the fabricated channel, trapping and transport of individual microparticles have been successfully demonstrated. This channel-integrated optoelectrofluidic device may be useful for several in-channel applications based on the optoelectrofluidics such as optoelectronic flow control, droplet-based protein assay and bead-based immunoassay.

• Korean Chemical Engineering Research
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• 제62권1호
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• pp.105-111
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• 2024

SLA (Stereo Lithography Apparatus) 방식은 액체 상태의 광경화성 레진(Resin)이 자외선 레이저에 닿으면 고체가 되는 원리를 활용한 3D 프린팅 방식으로 다양한 분야에서의 활용도가 증가하고 있다. 본 연구에서는 이 SLA 3D 프린팅 출력물의 표면 특성 중 소수성과 투명도를 개선하여 미세 유체 시스템의 제작에 활용하기 위한 기초 연구를 수행하였다. SLA 출력물은 소수성 코팅 방법을 이용해 표면 소수성의 특성을 개선할 수 있었으나, 소수성 코팅 방법의 종류에 따라 다양한 환경에서의 코팅 유지력은 차이를 보였다. 또한, 미세 유체 시스템의 제작에 요구되는 충분한 투명도와 소수성의 특성을 함께 확보하기 위해 선행된 연구에서 제안한 투명도 확보 방법에 소수성 코팅을 적용하여 접촉각의 변화를 비교하였다. Teflon 코팅법이 이산화 티타늄 코팅법과 비교하여 우수한 투명도의 확보가 가능하며, 다양한 환경에 노출되었을 때 높은 코팅의 유지력을 가져 미세 유체 시스템의 제작에 활용되기에 적합한 소수성 코팅법으로 제안되었다. 마지막으로 본 연구를 통해 제안된 미세 유체 시스템의 제작에 적합한 소수성 코팅 방법인 Teflon 코팅법 중 Fluoropel 800을 이용하여 디지털 미세 유체 시스템 중 하나인 액적 접촉 충전 현상(Electrophoresis of Charged Droplet, ECD) 칩을 SLA 3D 프린팅으로 제작, 액적의 조작을 성공적으로 시연함으로써 SLA 3D 프린팅 기술의 미세 유체 시스템의 제작에 활용 가능성을 확인하였다.

• Korean Chemical Engineering Research
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• 제51권5호
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• pp.597-601
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• 2013

본 연구는 액적기반 미세유체 장치를 이용하여 단분산성 마이크로캡슐의 간단한 제조방법에 관한 것이다. 본 연구에서 제시한 제조 방법은 이중액적을 생성시키기 위해 기존의 복잡한 표면처리가 필요한 이중 유화과정을 대신하여 하나의 교차점을 가진 단일공정을 사용하고자 한다. 먼저, 분산상은 광중합이 가능한 ethoxylated trimethylolpropane triacrylate (ETPTA) 단량체와 fluorocarbon (FC-77) 오일을 사용하고 연속상은 poly(vinyl alcohol) (PVA) 수용액을 사용하였으며, 미세유체 채널 내부로 흘려 주면 하나의 교차점에 흐름이 집중되어 균일한 이중액적을 생성한다. 생성된 이중액적은 광중합을 통해 마이크로캡슐을 제조한다. 상기 방법은 ETPTA 유체의 부피유속을 조절하여 이중액적의 껍질두께 제어가 가능하고 연속상인 물의 부피유속을 조절하여 전체 직경을 제어할 수 있다. 더 나아가, 본 시스템을 사용하여 다양한 물질들을 함입한 마이크로캡슐을 제작할 수 있으며, 약물전달시스템의 응용 기술에 활용될 것으로 예측된다.