Person: Kim, Philseok
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Kim, Philseok
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Publication Dynamic daylight control system implementing thin cast arrays of polydimethylsiloxane-based millimeter-scale transparent louvers(Elsevier BV, 2014) Park, Daekwon; Kim, Philseok; Alvarenga, Jack; Jin, Keojin; Aizenberg, Joanna; Bechthold, MartinThe deep building layouts typical in the U.S. have led to a nearly complete reliance on artificial lighting in standard office buildings. The development of daylight control systems that maximize the penetration and optimize the distribution of natural daylight in buildings has the potential for saving a significant portion of the energy consumed by artificial lighting, but existing systems are either static, costly, or obstruct views towards the outside. We report the Dynamic Daylight Control System (DDCS) that integrates a thin cast transparent polydimethylsiloxane (PDMS)-based deformable array of louvers and waveguides within a millimeter-scale fluidic channel system. This system can be dynamically tuned to the different climates and sun positions to control daylight quality and distribution in the interior space. The series of qualitative and quantitative tests confirmed that DDCS exceeds conventional double glazing system in terms of reducing glare near the window and distributing light to the rear of the space. The system can also be converted to a visually transparent or a translucent glazing by filling the channels with an appropriate fluid. DDCS can be integrated or retrofitted to conventional glazing systems and allow for diffusivity and transmittance control.Publication Liquid-Infused Silicone As a Biofouling-Free Medical Material(American Chemical Society (ACS), 2014) MacCallum, Noah; Howell, Caitlin; Kim, Philseok; Sun, Derek; Friedlander, Ronn; Ranisau, Jonathan; Ahanotu, Onye; Lin, Jennifer J.; Vena, Alexander; Hatton, Benjamin; Wong, Tak-Sing; Aizenberg, JoannaThere is a dire need for infection prevention strategies that do not require the use of antibiotics, which exacer- bate the rise of multi- and pan-drug resistant infectious organisms. An important target in this area is the bacterial attach- ment and subsequent biofilm formation on medical devices (e.g., catheters). Here we describe non-fouling, lubricant-infused slippery polymers as proof-of-concept medical materials that are based on oil–infused polydimethylsiloxane (iPDMS). Pla- nar and tubular geometry silicone substrates can be infused with non-toxic silicone oil to create a stable, extremely slippery interface that exhibits exceptionally low bacterial adhesion and prevents biofilm formation. Analysis of a flow culture of Pseudomonas aeruginosa through untreated PDMS and iPDMS tubing shows at least an order of magnitude reduction of bio- film formation on iPDMS, and almost complete absence of biofilm on iPDMS after a gentle water rinse. The iPDMS materials can be applied as a coating on other polymers or prepared as simply as taking a silicone tubing and immersing it in a sili- cone oil, and are compatible with traditional sterilization methods. As a demonstration, we show the preparation of sili- cone-coated polyurethane catheters and significant reduction of Escherichia coli and Staphylococcus epidermidis biofilm formation on the catheter surface. This work represents an important first step towards a simple and effective means of preventing bacterial adhesion on a wide range of materials used for medical devices.Publication Design of anti-icing surfaces: smooth, textured or slippery?(Springer Nature, 2016) Kreder, Michael; Alvarenga, Jack; Kim, Philseok; Aizenberg, JoannaPassive anti-icing surfaces, or icephobic surfaces, are an area of great interest because of their significant economic, energy and safety implications in the prevention and easy removal of ice in many facets of society. The complex nature of icephobicity, which requires performance in a broad range of icing scenarios, creates many challenges when designing ice-repellent surfaces. Although superhydrophobic surfaces incorporating micro- or nanoscale roughness have been shown to prevent ice accumulation under certain conditions, the same roughness can be detrimental in other environments. Surfaces that present a smooth liquid interface can eliminate some of the drawbacks of textured superhydrophobic surfaces, but additional study is needed to fully realise their potential. As more attention begins to shift towards alternative anti-icing strategies, it is important to consider and understand the nature of ice repellency in all environments to identify the limitations of current solutions and design new materials with robust icephobicity.Publication Condensation on slippery asymmetric bumps(Springer Nature, 2016) Park, Kyoo-Chul; Kim, Philseok; Grinthal, Alison; He, Neil; Fox, David; Weaver, James; Aizenberg, JoannaControlling dropwise condensation is fundamental to water- harvesting systems1–3, desalination4, thermal power generation4–8, air conditioning9, distillation towers10, and numerous other applications4,5,11. For any of these, it is essential to design surfaces that enable droplets to grow rapidly and to be shed as quickly as possible4–7. However, approaches4–8,10–21 based on microscale, nanoscale or molecular-scale textures suffer from intrinsic trade- offs that make it difficult to optimize both growth and transport at once. Here we present a conceptually different design approach— based on principles derived from Namib desert beetles3,22–24, cacti25, and pitcher plants17,26—that synergistically combines these aspects of condensation and substantially outperforms other synthetic surfaces. Inspired by an unconventional interpretation of the role of the beetle’s bumpy surface geometry in promoting condensation, and using theoretical modelling, we show how to maximize vapour diffusion flux20,27,28 at the apex of convex millimetric bumps by optimizing the radius of curvature and cross-sectional shape. Integrating this apex geometry with a widening slope, analogous to cactus spines, directly couples facilitated droplet growth with fast directional transport, by creating a free-energy profile that drives the droplet down the slope before its growth rate can decrease. This coupling is further enhanced by a slippery, pitcher-plant-inspired nanocoating that facilitates feedback between coalescence-driven growth and capillary-driven motion on the way down. Bumps that are rationally designed to integrate these mechanisms are able to grow and transport large droplets even against gravity and overcome the effect of an unfavourable temperature gradient. We further observe an unprecedented sixfold-higher exponent of growth rate, faster onset, higher steady-state turnover rate, and a greater volume of water collected compared to other surfaces. We envision that this fundamental understanding and rational design strategy can be applied to a wide range of water-harvesting and phase-change heat-transfer applications.Publication Pneumatically adaptive light modulation system (PALMS) for buildings(Elsevier BV, 2018) Hinz, K.; Alvarenga, Jack; Kim, Philseok; Park, D.; Aizenberg, Joanna; Bechthold, MartinThis research introduces a novel approach to control light transmittance based on flexible polydimethylsiloxane (PDMS) films that have been plasma-treated such that micro-scale surface features have a visual effect as the film responds to applied strain. The effect is continuously tunable from optically clear (71.5% Transmittance over a 400-900 nm wavelength) to completely diffuse (18.1% T). Changes in the film's optical properties are triggered by bi-axial strains applied using a pneumatic system to form pressurized envelopes. This paper reports on a series of experimental studies and provides system integration research using prototypes, simulations and geometric models to correlate measured optical properties, strain, and global surface curvatures. In conclusion, a design is proposed to integrate PDMS light control within existing building envelopes.Publication Structural Transformation by Electrodeposition on Patterned Substrates (STEPS): A New Versatile Nanofabrication Method(American Chemical Society (ACS), 2012) Kim, Philseok; Epstein, Alexander K; Khan, Mughees; Zarzar, Lauren; Lipomi, Darren J.; Whitesides, George; Aizenberg, JoannaArrays of high-aspect-ratio (HAR) nano- and microstructures are of great interest for designing surfaces for applications in optics, bio−nano interfaces, microelectromechanical systems, and microfluidics, but the difficulty of systematically and conveniently varying the geometries of these structures significantly limits their design and optimization for a specific function. This paper demonstrates a low-cost, high-throughput benchtop method that enables a HAR array to be reshaped with nanoscale precision by electrodeposition of conductive polymers. The method—named STEPS (structural transformation by electrodeposition on patterned substrates)—makes it possible to create patterns with proportionally increasing size of original features, to convert isolated HAR features into a closed-cell substrate with a continuous HAR wall, and to transform a simple parent two-dimensional HAR array into new three-dimensional patterned structures with tapered, tilted, anisotropic, or overhanging geometries by controlling the deposition conditions. We demonstrate the fabrication of substrates with continuous or discrete gradients of nanostructure features, as well as libraries of various patterns, starting from a single master structure. By providing exemplary applications in plasmonics, bacterial patterning, and formation of mechanically reinforced structures, we show that STEPS enables a wide range of studies of the effect of substrate topography on surface properties leading to optimization of the structures for a specific application. This research identifies solution-based deposition of conductive polymers as a new tool in nanofabrication and allows access to 3D architectures that were previously difficult to fabricate.Publication Extremely durable biofouling-resistant metallic surfaces based on electrodeposited nanoporous tungstite films on steel(Nature Pub. Group, 2015) Tesler, Alexander B.; Kim, Philseok; Kolle, Stefan; Howell, Caitlin; Ahanotu, Onyemaechi; Aizenberg, JoannaFormation of unwanted deposits on steels during their interaction with liquids is an inherent problem that often leads to corrosion, biofouling and results in reduction in durability and function. Here we report a new route to form anti-fouling steel surfaces by electrodeposition of nanoporous tungsten oxide (TO) films. TO-modified steels are as mechanically durable as bare steel and highly tolerant to compressive and tensile stresses due to chemical bonding to the substrate and island-like morphology. When inherently superhydrophilic TO coatings are converted to superhydrophobic, they remain non-wetting even after impingement with yttria-stabilized-zirconia particles, or exposure to ultraviolet light and extreme temperatures. Upon lubrication, these surfaces display omniphobicity against highly contaminating media retaining hitherto unseen mechanical durability. To illustrate the applicability of such a durable coating in biofouling conditions, we modified naval construction steels and surgical instruments and demonstrated significantly reduced marine algal film adhesion, Escherichia coli attachment and blood staining.Publication Fabrication and Replication of Arrays of Single- or Multicomponent Nanostructures by Replica Molding and Mechanical Sectioning(American Chemical Society (ACS), 2010) Lipomi, Darren J.; Kats, Mikhail A; Kim, Philseok; Kang, Sung; Aizenberg, Joanna; Capasso, Federico; Whitesides, GeorgeThis paper describes the fabrication of arrays of nanostructures (rings, crescents, counterfacing split rings, cylinders, coaxial cylinders, and other structures) by a four-step process: (i) molding an array of epoxy posts by soft lithography, (ii) depositing thin films on the posts, (iii) embedding the posts in epoxy, and (iv) sectioning in a plane parallel to the plane defined by the array of posts, into slabs, with an ultramicrotome (“nanoskiving”). This work demonstrates the combination of four capabilities: (i) formation of structures that are submicrometer in all dimensions; (ii) fabrication of 3D structures, and arrays of structures, with gradients of height; (iii) patterning of arrays containing two or more materials, including metals, semiconductors, oxides, and polymers; and (iv) generation of as many as 60 consecutive slabs bearing contiguous arrays of nanostructures. These arrays can be transferred to different substrates, and arrays of gold rings exhibit plasmonic resonances in the range of wavelengths spanning 2−5 μm.Publication Fluorogel Elastomers with Tunable Transparency, Elasticity, Shape-Memory, and Antifouling Properties(Wiley-Blackwell, 2014) Yao, Xi; Dunn, Stuart; Kim, Philseok; Duffy, Meredith Anne; Alvarenga, Jack; Aizenberg, JoannaOmniphobic fluorogel elastomers were prepared by photocuring perfluorinated acrylates and a perfluoropolyether crosslinker. By tuning either the chemical composition or the temperature that control the crystallinity of the resulting polymer chains, a broad range of optical and mechanical properties of the fluorogel can be achieved. After infusing with fluorinated lubricants, the fluorogels showed excellent resistance to wetting by various liquids and anti-biofouling behavior, while maintaining cytocompatiblity.Publication A bioinspired omniphobic surface coating on medical devices prevents thrombosis and biofouling(Nature Publishing Group, 2014) Leslie, Daniel; Waterhouse, Anna; Berthet, Julia B; Valentin, Thomas M; Watters, Alexander; Jain, Abhishek; Kim, Philseok; Hatton, Benjamin D; Nedder, Arthur; Donovan, Kathryn; Super, Elana H; Howell, Caitlin; Johnson, Christopher P; Vu, Thy L; Bolgen, Dana; Rifai, Sami; Hansen, Anne; Aizenberg, Michael; Super, Michael; Aizenberg, Joanna; Ingber, DonaldThrombosis and biofouling of extracorporeal circuits and indwelling medical devices cause significant morbidity and mortality worldwide. We describe a bioinspired coating that repels blood from virtually any material by covalently tethering a molecular layer of perfluorocarbon, which holds a thin liquid film of medical-grade perfluorocarbon on the substrate surface, mimicking the liquid layer certain plants use to prevent adhesion. This coating prevents fibrin attachment, reduces platelet adhesion and activation, suppresses biofilm formation, and is stable under blood flow in vitro. Surface-coated medical-grade tubing and catheters, assembled into arteriovenous shunts and implanted in living pigs, remain patent for at least 8 hours without anticoagulation. This coating technology offers the potential to significantly reduce anticoagulation in patients while preventing thrombotic occlusion and biofouling of medical devices.