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RISS 인기검색어
- 검색키워드
- 저자 : Farshchian Bahador (검색결과 5 건)
- 무료
- 기관 내 무료
- 유료
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Scaling and mechanism of droplet array formation on a laser-ablated superhydrophobic grid
Farshchian, Bahador,Gatabi, Javad R.,Bernick, Steven M.,Lee, Gwan-Hyoung,Droopad, Ravindranath,Kim, Namwon Elsevier 2018 Colloids and surfaces. A, Physicochemical and engi Vol.547 No.-
<P><B>Abstract</B></P> <P>Superhydrophobic grid patterns were ablated on a hydrophobic polydimethylsiloxane (PDMS) substrate using a nanosecond pulsed laser. The substrate with a wettability contrast (superhydrophobic-hydrophobic) was vertically immersed in a pool of water and withdrawn at different speeds to form droplet arrays spontaneously. The size of droplets was tuned by controlling the withdrawal speed (<I>S</I> <SUB>w</SUB>), which resulted in different contact line speeds on non-irradiated cell (NIC) and laser-irradiated grid (LIG) areas with different surface properties of no-slip and partial-slip conditions, respectively. The ratio of the contact line speeds on NIC and LIG areas (<I>S</I> <SUB>NIC</SUB>/<I>S</I> <SUB>LIG</SUB>) decreased exponentially with the withdrawal speed, leading to formation of larger droplets on NIC. A geometric scaling model predicted the size of droplets formed on NIC arrays over a range of contact line speeds on NIC and LIG, the ratio of the contact line speeds, the withdrawal speed, and the size of NIC.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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3D nanomolding and fluid mixing in micromixers with micro-patterned microchannel walls
Farshchian Bahador,Amirsadeghi Alborz,Choi Junseo,Park Daniel S.,Kim Namwon,Park Sunggook 나노기술연구협의회 2017 Nano Convergence Vol.4 No.4
Microfluidic devices where the microchannel walls were decorated with micro and nanostructures were fabricated using 3D nanomolding. Using 3D molded microfluidic devices with microchannel walls decorated with microscale gratings, the fluid mixing behavior was investigated through experiments and numerical simulation. The use of microscale gratings in the micromixer was predicated by the fact that large obstacles in a microchannel enhances the mixing performance. Slanted ratchet gratings on the channel walls resulted in a helical flow along the microchannel, thus increasing the interfacial area between fluids and cutting down the diffusion length. Increasing the number of walls decorated with continuous ratchet gratings intensified the strength of the helical flow, enhancing mixing further. When ratchet gratings on the surface of the top cover plate were aligned in a direction to break the continuity of gratings from the other three walls, a stack of two helical flows was formed one above each other. This work concludes that the 3D nanomolding process can be a cost-effective tool for scaling-up the fabrication of microfluidic mixers with improved mixing efficiencies.
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Laser-induced superhydrophobic grid patterns on PDMS for droplet arrays formation
Farshchian, Bahador,Gatabi, Javad R.,Bernick, Steven M.,Park, Sooyeon,Lee, Gwan-Hyoung,Droopad, Ravindranath,Kim, Namwon Elsevier 2017 APPLIED SURFACE SCIENCE - Vol.396 No.-
<P><B>Abstract</B></P> <P>We demonstrate a facile single step laser treatment process to render a polydimethylsiloxane (PDMS) surface superhydrophobic. By synchronizing a pulsed nanosecond laser source with a motorized stage, superhydrophobic grid patterns were written on the surface of PDMS. Hierarchical micro and nanostructures were formed in the irradiated areas while non-irradiated areas were covered by nanostructures due to deposition of ablated particles. Arrays of droplets form spontaneously on the laser-patterned PDMS with superhydrophobic grid pattern when the PDMS sample is simply immersed in and withdrawn from water due to different wetting properties of the irradiated and non-irradiated areas. The effects of withdrawal speed and pitch size of superhydrophobic grid on the size of formed droplets were investigated experimentally. The droplet size increases initially with increasing the withdrawal speed and then does not change significantly beyond certain points. Moreover, larger droplets are formed by increasing the pitch size of the superhydrophobic grid. The droplet arrays formed on the laser-patterned PDMS with wettability contrast can be used potentially for patterning of particles, chemicals, and bio-molecules and also for cell screening applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Superhydrophobic grid patterns were processed on the surface of PDMS using a pulsed nanosecond laser. </LI> <LI> Droplet arrays form instantly on the laser-patterned PDMS with the superhydrophobic grid pattern when the PDMS sample is simply immersed in and withdrawn from water. </LI> <LI> Droplet size can be controlled by controlling the pitch size of superhydrophobic grid and the withdrawal speed. </LI> </UL> </P>
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Choi, Junseo,Farshchian, Bahador,Kim, Jinsoo,Park, Sunggook American Scientific Publishers 2013 Journal of Nanoscience and Nanotechnology Vol.13 No.6
<P>Artificial membranes with perforated nanopores in defined locations provide an important biomimicking platform for sensing and analysis of biomolecules. This study presents a simple and flexible method to fabricate a freestanding polymer membrane with perforated micro- and nanopores using a combination of nanoimprint lithography (NIL) and pressed self-perfection (PSP) process. NIL was used to define initial pores of a few micrometers in diameter in the SU-8 membrane layer, which was followed by the PSP process where the patterned SU-8 membrane is pressed with a blank silicon wafer at an elevated temperature. This PSP process results in a lateral flow of the SU-8 resist and consequently reduces the pore size in the membrane. With this method, we have demonstrated fabrication of a SU-8 membrane with perforated pores down to approximately 300 nm in diameter. The results indicate that by employing a pore reduction process nanopore membranes can be manufactured without requirements of having a stamp with nanoscale structures and high aspect ratio imprinting with the stamp.</P>
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Low cost fabrication of a superhydrophobic V-grooved polymer surface.
Hurst, Steven M,Farshchian, Bahador,Brumfield, Lance,Ok, Jeong Tae,Choi, Junseo,Kim, Jinsoo,Parkl, Sunggook American Scientific Publishers 2013 Journal of Nanoscience and Nanotechnology Vol.13 No.3
<P>Engineering of polymer surfaces to control their wetting properties has shown a wide range of potential applications. In this paper we show low cost fabrication of a superhydrophobic polymer surface via a hierarchical combination of hot embossing, O2 reactive ion etching (RIE) and deposition of a hydrophobic silane. The hot embossing and O2 RIE were used to produce respective micro and nanoscale surface roughness which is a requirement for obtaining superhydrophobic surfaces, while the deposition of a hydrophobic silane modified surface chemistry. In order to increase the water/air interface in the Cassie-Baxter composite wetting model, a brass mold with microscale V-grooves was used for hot embossing. Images of droplets in both static water contact angles and dynamic impact tests with the surface clearly show that the wetting state follows the Cassie-Baxter wetting model. The results of this study indicate that our design of the dual level surface roughness and the fabrication process allow for low cost and easy production of a highly superhydrophobic surface.</P>
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