Unidirectional wetting and spreading on stooped polymer nanohairs

Kim, Tae-il,Suh, Kahp Y. Royal Society of Chemistry 2009 SOFT MATTER Vol.5 No.21

<P>We report on unidirectional wetting and spreading of a water droplet on stooped polymer nanohairs fabricated by replica molding and oblique electron beam irradiation. When a droplet is placed on the surface with high aspect-ratio (AR ∼ 10) directionally bent nanohairs, it wets and spontaneously spreads over the surface in a unidirectional manner along the stooped direction with one edge being pinned to the substrate. To evaluate such anisotropic wetting property, the liquid velocity is measured along and against the stooped direction inside a simple Y-shaped microchannel with a syringe pump after channel bonding. It is found that the velocity is about six times faster along the stooped direction than that against the stooped direction, suggesting that this simple strategy would find uses in microfluidics and other applications involving unidirectional liquid manipulation.</P> <P>Graphic Abstract</P><P>We report on unidirectional wetting and spreading of a water droplet on stooped polymer nanohairs fabricated by replica molding and oblique electron beam irradiation. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b915079j'> </P>

Measurement of Viscosity of Confined Polymer Melt Using Capillary Kinetics

Suh, Kahp Y.,Kim, Pilnam,Jeong, Hoon Eui,Kim, Jae Kwan Taylor Francis 2006 Nanoscale and microscale thermophysical engineerin Vol.10 No.3

<P> We present a simple method to measure viscosity of thin polymer melt that is confined between a substrate and a permeable plate using a modified Poiseuille equation. When a patterned polydimethylsiloxane (PDMS) mold is placed on a styrene-butadiene-styrene (SBS) block copolymer film spin-coated onto a substrate and heated above the polymer's glass transition temperature, capillarity forces the polymer melt into the void of the channel. To calculate the viscosity of the confined polymer melt, the height of capillary rise was measured as a function of time for a number of film thicknesses (220, 350, 540, 1000, and 1300 nm) and at two different temperatures (70 and 100°C). It was found that the viscosity increases with decreasing film thickness at 70°C, whereas it decreases with decreasing film thickness at 100°C. This discrepancy might be related to the confinement-induced solid-like behavior of the polymer melt and wall slip at the polymer/solid interface. Furthermore, the viscosity turned out to be nearly equal to the bulk value for relatively large film thickness (> ∼ 500 nm) regardless of the temperature, which corresponds to earlier findings.</P>

Surface-Tension-Driven Patterning: Combining Tailored Physical Self-Organization with Microfabrication Methods

Suh, Kahp ,Y. WILEY-VCH Verlag 2006 Small Vol.2 No.7

<B>Graphic Abstract</B> <P>Small features: One of the great current challenges is to find new techniques that reliably further reduce the scale at which patterns can be reproduced for the electronics industry, amongst others. A recent study provides a major advance in controlling surface-tension-driven self-organization in combination with a traditional microfabrication method to produce regularly spaced line patterns in an evaporating thin film through guided evaporation and dewetting (see figure). <img src='wiley_img/16136810-2006-2-7-SMLL200600121-content.gif' alt='wiley_img/16136810-2006-2-7-SMLL200600121-content'> </P>

Reversibly bonded nanocapillaries by electrostatic forces for directed alignment of carbon nanotubes

Pilnam Kim(김필남),Kahp Y. Suh(서갑양) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11

Reversibly bonded nanocapillaries (500 ? 50 ㎚) were fabricated on gold and silicon substrates using electrostatic forces that can be generated on a rigiflex mold upon removal from an original, engraved silicon master. Polyethylene glycol diacrylate (PEG-DA) was used as a rigiflex mold material with highly negative surface charges (zeta potential: - 113.55 ㎽).). The rigiflex, transparent PEG-DA mold spontaneously wets gold or silicon substrate via electrostatic attraction, forming reversibly bonded nanocapillaries without any surface modifications or external stimuli. Using these nanocapillaries, nanolines or nanowells were fabricated without residual layer along with one-dimensional arrays of single-walled carbon nanotubes (SWCNTs) and gold nanoparticles(NPs).

Step-and-repeat process for thermal nanoimprint lithography

Yoon, Hyunsik,Cho, Hye Sung,Suh, Kahp Y,Char, Kookheon IOP Pub 2010 Nanotechnology Vol.21 No.10

<P>We present a step-and-repeat process for thermal nanoimprint lithography. For the selective heating and imprinting, a spin-coated polystyrene layer is exposed to infra-red rays from a halogen lamp (intensity ∼ 500 W) with a metal-covered glass while pressed with a transparent polymer mold (Young’s modulus ∼ 300 MPa) under a pressure of ∼ 4 bar for 60–120 s. During imprinting, the non-irradiated region is protected by a metal screen and a heat sink consisting of a copper block at the bottom which prevents the pattern collapse by lateral heat conduction from the irradiated region.</P>

Solvent-Assisted Decal Transfer Lithography by Oxygen-Plasma Bonding and Anisotropic Swelling

Kim, Pilnam,Kwak, Rhokyun,Lee, Sung Hoon,Suh, Kahp Y. WILEY-VCH Verlag 2010 Advanced Materials Vol.22 No.22

<B>Graphic Abstract</B> <P>Solvent-assisted decal transfer lithography (DTL) enables the formation of well-defined micro-/nanostructures over a large area (∼4 in. wafer) by combining irreversible oxygen bonding and anisotropic swelling of poly(dimethoxylsiloxane) (PDMS). Such swelling-induced stress gradient allows for cohesion failure of the skin layer upon removal of the stamp, leaving behind a highly uniform layer (∼100 nm). <img src='wiley_img_2010/09359648-2010-22-22-ADMA200903440-content.gif' alt='wiley_img_2010/09359648-2010-22-22-ADMA200903440-content'> </P>

Inorganic polymer photoresist for direct ceramic patterning by photolithography

Pham, Tuan Anh,Kim, Pilnam,Kwak, Moonkyoo,Suh, Kahp Y.,Kim, Dong-Pyo Royal Society of Chemistry 2007 Chemical communications Vol.2007 No.39

<P>A novel negative, inorganic polymer photoresist was demonstrated to be suitable for simple and direct fabrication of tribological SiCN-based ceramic microstructures <I>via</I> UV photolithography and subsequent pyrolysis at 800 °C.</P> <P>Graphic Abstract</P><P>A novel negative, inorganic polymer photoresist was demonstrated to be suitable for simple and direct fabrication of tribological SiCN-based ceramic microstructures <I>via</I> UV photolithography and subsequent pyrolysis at 800 °C. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b708480c'> </P>

Evolution of transient meniscus in a wettable microchannel for Newtonian fluid

Kim, Seung Mo,Lee, Woo Il,Suh, Kahp Y IOP 2006 Journal of micromechanics and microengineering Vol.16 No.12

<P>A simple numerical approach based on the volume of fluid (VOF) method reveals that a ‘W’-shaped, transient meniscus is ubiquitous during the formation of a uniformly curved meniscus within a microchannel, which has been believed to be dominant for the transients. The time that is needed to maintain the transient meniscus is correlated with viscosity, surface tension and geometry of the cavity. A generalized correlation is presented to predict the persistent time of the transient meniscus in a wettable microchannel (contact angle, &thetas; < 90?) for Newtonian fluid.</P>

Stabilization of Ion Concentration Polarization Using a Heterogeneous Nanoporous Junction

Kim, Pilnam,Kim, Sung Jae,Han, Jongyoon,Suh, Kahp Y. American Chemical Society 2010 NANO LETTERS Vol.10 No.1

<P>We demonstrate a recycled ion-flux through heterogeneous nanoporous junctions, which induce stable ion concentration polarization with an electric field. The nanoporous junctions are based on integration of ionic hydrogels whose surfaces are negatively or positively charged for cationic or anionic selectivity, respectively. Such heterogeneous junctions can be matched up in a way to achieve continuous ion-flux operation for stable concentration gradient or ionic conductance. Furthermore, the combined junctions can be used to accumulate ions on a specific region of the device.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2010/nalefd.2010.10.issue-1/nl9023319/production/images/medium/nl-2009-023319_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl9023319'>ACS Electronic Supporting Info</A></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl9023319'>ACS Electronic Supporting Info</A></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl9023319'>ACS Electronic Supporting Info</A></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl9023319'>ACS Electronic Supporting Info</A></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl9023319'>ACS Electronic Supporting Info</A></P>

Optical Lithography with Printed Metal Mask and a Simple Superhydrophobic Surface

Kim, Tae-il,Baek, Chang hoon,Suh, Kahp Y.,Seo, Soon-min,Lee, Hong H. WILEY-VCH Verlag 2008 Small Vol.4 No.2

<B>Graphic Abstract</B> <P>A nanolithographic optical patterning technique is presented. A metal pattern on a mold is transferred onto a photoresist on a substrate, then the resist with the printed metal mask is flood illuminated. The light passes through only the resist lenses that are formed in the transfer process. Focusing by these lenses results in a significant reduction in the feature size. <img src='wiley_img/16136810-2008-4-2-SMLL200700882-content.gif' alt='wiley_img/16136810-2008-4-2-SMLL200700882-content'> </P>