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미세 유체 시스템에서 전하와 이온의 능동적 제어 방법에 관한 연구

미세 유체 시스템에서 전하와 이온의 능동적 제어 방법에 관한 연구
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In this dissertation, active control methods of charge and ion in micro/nano fluidic system are presented and can be divided into three individual parts. In first part, Electrohydrodynamic Droplet Repulsion (EDR), which can be applicable to microdroplet manipulation and patterning, is presented. In second part, novel ICP desalination device is fabricated and shows good performances. In the last part, we revealed hidden gap, triangular nanochannel, and present tunable ion transport platform in nanofluidic system. In the first part, control technique for charged water droplets, named as Electrohydrodynamic Droplet Repulsion (EDR), is reported. Charged droplets emitting from a capillary and falling down toward an insulating substrate are deflected from their intended impact point due to the like polarity of previously fallen droplets. The mechanism for this potentially critical phenomenon is explained by applying a theoretical model describing the balance between gravitational and Coulomb forces acting on a droplet. In addition to theoretical analysis of EDR, we report a novel method to form a circular pattern of monodisperse microdroplets using EDR. In addition to regular EDR system, by placing a ring electrode between capillary and ground substrate, two separate regions were created. Parameter study of two regions was carried for droplet formation and falling velocity to control the radius of the generated droplets and the circular patterns independently. Based on energy conservation theory, our experimental results showed that the free falling region exerted crucial influences on the sizes of the circular patterns. In the second part, low cost and single step removal system of multiple heavy metals by Ion Concentration Polarization (ICP). Groundwater contamination by heavy metal compounds, such as arsenic, cadmium and lead, poses significant public health challenges, especially in developing countries of the world. Existing water purification strategies for heavy metal removal are not readily applicable due to many technological, environmental, and economical barriers. Based on our previous ion concentration polarization (ICP) water purification process, we are reporting a small scale water purification system that is made of low cost, manufacturable materials and processes. We demonstrate that the system can simultaneously eliminate more than 99% of arsenic, cadmium, and lead contained in the water modeled after Bangladeshi ground water, reducing their concentrations below the safety limit in a single step process. The same system can also be used for desalination of water (NaCl: 30,000TDS, seawater concentration) at the power efficiency of ~5Wh/L, at the membrane efficiency of 0.7 mL/min/cm2 and 50 % recovery rate. The energy efficiency, removal efficiency, and low cost and manufacturability of this system hold a strong promise for portable, self-powered water purification / desalination system that can have an impact on water shortage in developing / rural part of the world. In the third parts, a simple and economic, but reliable nanochannel fabrication technique, leading a heterogeneously charged triangular nanochannel is reported. The nanochannel utilized the elasticity of PDMS when it bonded with micron-scale structure on a substrate. Secondly we successfully demonstrated novel ionic transportations by tweaking the micron structures
(1) the transition of nonlinear ionic conductance depending on the nanochannel properties and (2) the ionic field-effect transistor. Nanochannel conductance has two distinguishable nonlinear regimes called “surface-charge-governed” and “geometry-governed” regime and its only individual overlooks were frequently reported. However, the transition between two regimes by adjusting nanochannel properties has not been reported due to the difficulty of functional nanochannel fabrication. In addition, a gate voltage was comfortably applied to the triangular nanochannel so that the field-effect ion transportation was reliably achieved. Therefore, presenting triangular nanochannels have critical advantages over its heterogeneous and tunable surface properties and thus, could be effective means as an active fundamental to control and manipulate the ion-electromigration through a nanofluidic system.
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