Facile Fabrication and Patterning Study of Superhydrophilic/phobic Surfaces

Abstract

In dissertation, research about fabrication and patterning of the superhydrophilic/phobic surfaces was conducted. Applications of fabrication and patterning techniques such as surface drag reduction, nano dispensing, and mass production patterning were introduced with experimental results. Hydrophobic surfaces with micro- or nanoscale pillars have been attracting considerable interest from scientists. In nature, such surfaces can be found on lotus leaves or under the feet of pond skaters. One significant property of these surfaces is friction drag reduction (FDR). Many studies have been conducted to demonstrate this reduction in terms of laminar and turbulent flows. The slip-length hypothesis is often used to explain this phenomenon. In this study, processes with the advantages of simplicity and cost effectiveness were used to fabricate dual-scale structures. Durable super-hydrophilic and super-hydrophobic surfaces were easily obtained from these structures. FDR was measured on a super-hydrophobic surface and was compared to that on smooth and super-hydrophilic surfaces. The experimental results in a circulating water channel revealed the Reynolds number range within which substantial FDR can occur on a super-hydrophobic surface. The mechanism of FDR and the role of slip are discussed by comparing experimental results. Owing to the fact that liquid-dispensing devices are used in a wide variety of scientific fields, including chemistry, biology, pharmacology, and mechanics, droplet dispensing has come to be regarded as a key technology with respect to micro/nanoengineering. Positive-placement dispensing technology is being used widely because it allows for a high degree of controllability without requiring a complex dispensing system; however, adhesion and slip-related issues limit the performance of this technology. In this letter, we report a technique for the fabrication of selective superhydrophilic/phobic coatings in syringe-type positive-displacement dispensing nozzle tips. The superhydrophilic capillary in the nozzle tip was coated selectively with superhydrophobic materials by exploiting the difference in the capillary pressure. The surface of the front part of the capillary was made superhydrophobic; it thus allowed the liquid to flow without adhesion. In contrast, the back part was made superhydrophilic; it retarded the flow of the liquid, holding it in place. Together, the two surfaces minimized the volume of the dispensed droplets. High-speed images of the dispensed liquid were taken to compare the two droplet-dispensation processes. It was found that the volume of the water droplets dispensed from the selectively coated nozzle tip was as low as 27 nL and much smaller than that of the droplets dispensed from the superhydrophobic nozzle tip. Patterning techniques are essential to many research fields such as chemistry, biology, medicine, and micro-electromechanical systems (MEMS). In this Letter, we report a simple, fast, and low-cost superhydrophobic patterning method using a superhydrophilic template. The technique is based on the contact stamping of the surface during hydrophobic dip coating. Surface characteristics were measured using scanning electron microscopy and energy-dispersive X-ray spectroscopic analysis. The results showed that the hydrophilic template, which was contacted with the stamp, was not affected by the hydrophobic solution. The resolution study was conducted using a stripe shaped stamp. The patterned line was linearly proportional to the width of the stamp line with a constant narrowing effect. A surface with regions of four different types of wetting was fabricated to demonstrate the patterning performance.

최근 극친수/ 극소수성 표면 제작 및 응용에 대한 다양한 연구가 이루어지고 있다. 연꽃잎의 표면 구조를 통해 표면의 계층구조 및 표면 성질이 극친수/극소수 표면 제작에 중요한 요소임을 알게 된 후 이를 모사하기 위한 많은 시도가 진행되었다. MEMS, 리쏘그래피, UV 조사, 증착 등 다양한 방법을 통해 극친수/극소수 표면이 제작되었지만 실제 산업 분야로의 응용을 위해 보다 쉽고 저가의 제작 공정에 대한 요구가 이어져왔다. 또한 표면의 특정한 부분이나 복잡한 형상의 내, 외부의 젖음성을 달리 구현하기 위한 패터닝 방법에 관한 연구또한 기존의 잉크젯 방식, 마스크 방식등의 단점을 보완할 필요성이 대두되었다. 이 논문에서는 한 번의 간단한 공정으로 손쉽게 계층구조를 갖는 극친수/극소수 표면의 제작 방법에 대해소개하고, 보다 대량생산에 적합하고 저가인 표면 젖음성 패터닝 기술에 대해 소개한다. 양극산화를 통한 나노 플레이크 구조의 극친수/극소수 표면 제작, 모세관 압을 이용한 복잡한형상의 내,외부 패터닝, 스탬프를 이용한 패터닝 공정에 관한 연구가 진행되었고 각 공정 결과에 대한 유체 저항, 액적 분사, 패터닝 정밀도 실험이 진행되었다.