Browsing by Author "Kota, Arun K., advisor"
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Item Open Access Design of durable de-icing, superhydrophobic, superoleophobic coatings(Colorado State University. Libraries, 2015) Beemer, Darryl Lewis, author; Kota, Arun K., advisor; Bailey, Travis, committee member; Popat, Ketul, committee memberThis work looks at the issue of ice accretion on surfaces and efforts to reduce this ice accretion and the subsequent ice adhesion strength in order to make ice removal easier and more cost effective for wider implementation. Ice accretion on various surfaces is a major economic and safety issue for a variety of industries, including air travel, power production and transmission, maritime shipping, and more. While efforts have been taken to diminish ice accretion and subsequent ice adhesion strength, existing technology is limited in its ability to prevent ice accretion in a wide range of conditions and to then have a low ice adhesion strength once ice has accumulated on a surface. With the background of icing and solid mechanics of ice removal in mind, materials were developed to exhibit a low ice adhesion strength while maintaining the durability characteristic of a non-sacrificial coating. After development and testing, it was found that the developed materials exhibited an adhesion strength lower than any currently available technology, with extended durability under both ice removal and mechanical abrasion conditions. As a secondary effort, an initial exploration into the development of durable superomniphobic surfaces was performed in order to reduce and/or prevent adhesion of water-based paint and a low surface-tension fluid to various surfaces. Development of a variety of surface types (spray coated layered and mixed surfaces, etched stainless steel surfaces, and more) was performed, with initial results providing an encouraging path forward for future development of this durable coating work.Item Open Access Fabrication of natural and magnetic slippery surfaces(Colorado State University. Libraries, 2019) Sutherland, Daniel James, author; Kota, Arun K., advisor; Popat, Ketul, committee member; Park, Juyeon, committee memberLiquid-infused porous surfaces (LIPS) are a type of low adhesion surfaces. They allow most common solids and liquids to slide off the surface easily. Because of this they are able to reduce the adhesion of food, ice, and even blood platelets to surfaces. As a result, LIPS have applications in reducing food waste, aircraft and powerlines deicing, and hemocompatable implants. However, most LIPS are made of toxic fluorocarbon materials. In this work, in order to eschew toxic fluorocarbon materials, we designed several LIPS made from natural hemp products. The first is an all-natural LIPS made from hemp fibers, which could help reduce or eliminate liquid food waste. The second is an aluminum LIPS that shows excellent anti-icing and de-icing properties. The third is a titanium nanotube LIPS that allows blood to slide off without impinging or clotting. This surface also shows excellent platelet reduction. Finally, we demonstrated a simple way of replicating this LIPS system on multiple metals including copper and steel. Further, we demonstrated a simple fabrication of LIPS on top of the fabricated texture atop a magnetic tape. Magnetic tapes are no longer widely used and they are extremely difficult to dispose of. In this magnetic tape-based LIPS, we were able to use an external magnet to manipulate droplets on the surface of the magnetic tape. This can lead to a microfluidic system with a repurposed substrate and precise manipulation of droplets using a magnetic field.Item Open Access Fabrication of omniphobic and superomniphobic surfaces(Colorado State University. Libraries, 2017) Pendurthi, Anudeep, author; Kota, Arun K., advisor; Yalin, Azer P., advisor; Kipper, Matt J., committee memberSuperomniphobic surfaces (i.e., surfaces that are extremely repellent to both high surface tension liquids like water and low surface tension liquid like oils and alcohols) can be fabricated through a combination of surface chemistry that imparts low solid surface energy and a re-entrant surface texture. Recently, surface texturing with lasers has received significant attention because laser texturing is scalable, solvent-free, and can produce a monolithic texture (i.e., a texture that is an integral part of the surface unlike a coating that is deposited on the underlying substrate) on virtually any material. In this work, we fabricated nanostructured omniphobic and superomniphobic surfaces with stainless steel 430, stainless steel 316, stainless steel 304, titanium, aluminum and glass surfaces using a simple, inexpensive and commercially available CO2 laser engraver. Further, we demonstrated that the nanostructured omniphobic and superomniphobic surfaces fabricated using our laser texturing technique can be used to design patterned surfaces, surfaces with discrete domains of the desired wettability and on-surface microfluidic devices. Systematic experiments were conducted to evaluate the importance of various laser parameters to fabricate these omniphobic and superomniphobic surfaces. Also, the performance of these surfaces under adverse acidic and basic conditions was evaluated systematically. In addition to surface texturing with lasers, in this work, we also report a simple and versatile method to fabricate superomniphobic glass microfiber paper by growing silicone nanofilaments using trichloromethylsilane (TCMS).Item Open Access Fabrication of slippery textured and slippery non-textured surfaces(Colorado State University. Libraries, 2018) Cackovic, Matthew, author; Kota, Arun K., advisor; Popat, Ketul, committee member; Bailey, Travis, committee memberSlippery surfaces, i.e., surfaces that have high droplet mobility and low lateral adhesion for liquid droplets, have a wide range of application such as condensation heat transfer, anti-corrosion, lab-on-chip devices, etc. These surfaces can be categorized into smooth slippery surfaces and super-repellant textured slippery surfaces. In this work, we fabricated super-repellant textured superomniphobic paper surfaces. We developed a simple and facile method to fabricate superomniphobic paper surface by growing silicone nanofilaments on a glass microfiber paper surface before imparting low solid surface energy to give the surface the appropriate texture and chemistry. We characterized the performance of our surface and demonstrated our surfaces potential as a lab-on-chip type device. We showed high droplet transport rate, created a simple on-paper pH sensor, demonstrated weight bearing, and showed separation of water from ultra-low surface tension hexane demonstrating the utility of our superomniphobic paper surfaces. We also fabricated a smooth slippery copper surface by creating a chemically and physically homogenous surface. We developed a quick screening test to evaluate the performance of our surfaces in addition to the traditional tests. We showed smoother surfaces performed better and were more slippery.Item Open Access Superhydrophobic coatings for electrical insulators(Colorado State University. Libraries, 2018) Vallabhuneni, Sravanthi, author; Kota, Arun K., advisor; Popat, Ketul, committee member; Kipper, Matt J., committee memberDielectric breakdown in electrical insulators is a frequently encountered phenomenon leading to surface damage, material loss and eventually a complete breakdown of electrical insulators. Dielectric breakdown is accelerated under severe conditions such as humidity and rain. As a result, the service life of the electrical insulators is affected. In our work, we employed superhydrophobic coatings, which are extremely repellent towards water, in an attempt to retain the dielectric strength of electric insulators in the presence of water. In addition, we studied the influence of surface roughness on the dielectric breakdown of electrical insulators. In this work, hydrophobic PDMS sheets (as a mimic to silicone bushings/insulators) with different surface roughness were fabricated and superhydrophobicity was imparted to these sheets via surface modification. The dielectric breakdown of these PDMS sheets was studied under both dry and wet conditions. The influence of surface roughness on the dielectric breakdown was also investigated by using PDMS sheets with different surface roughness. We noticed an increase in surface roughness leads to lower dielectric breakdown. Further, we demonstrated that superhydrophobic coatings on the surface of electrical insulators allow the retention of dielectric strength under wet conditions. Consequently, we envision that superhydrophobic coatings on electrical insulators will lead to enhanced performance and prolonged service life of insulators.Item Open Access Superhydrophobic surfaces for reducing liquid adhesion and contact time(Colorado State University. Libraries, 2017) Boyd, Lewis Marinoff, author; Kota, Arun K., advisor; Popat, Ketul, committee member; Reynolds, Melissa, committee memberSuperhydrophobic surfaces are extremely repellent to water and aqueous liquids. Water droplets can bead up, bounce and easily roll off from superhydrophobic surfaces. Consequently, superhydrophobic surfaces can be used to reduce liquid adhesion to food containers and manufacturing equipment which is a significant problem for food packaging and agricultural industries. In this work, in order to reduce liquid waste in food containers, a novel superhydrophobic coating made with natural, edible materials was developed and fabricated. The superhydrophobic coatings made with edible materials virtually eliminate liquid waste in food containers. Systematic experiments were conducted on superhydrophobic coatings and non-textured, low adhesion films to evaluate the performance of the coatings and films in reducing liquid adhesion to manufacturing equipment. In high shear environments such as manufacturing equipment, non-textured, low adhesion films perform better than superhydrophobic coatings due to their improved durability. Further, superhydrophobic surfaces can be used to reduce the time an impacting liquid droplet is in contact with the surface (contact time), which in turn is useful for anti-icing applications. In this work, superhydrophobic surfaces with and without macroscale texture were design, fabricated and evaluated for their contact time with water droplets. The contact time was significantly lower on macroscale textured superhydrophobic surfaces (i.e., better for anti-icing) compared with superhydrophobic surfaces without macroscale texture.Item Open Access Tailoring solid-liquid interactions to control droplet wetting and dynamics(Colorado State University. Libraries, 2019) Vahabi, Hamed, author; Kota, Arun K., advisor; Dasi, Lakshmi Prasad, committee member; Tavener, Simon, committee member; Bandhauer, Todd M., committee memberRecent advances in micro/nano-scale fabrication techniques and synthesis of novel chemicals with a variety of functionalities have opened up new avenues in tailoring solid-liquid interactions. In this work, by systematically tuning the wettability and slipperiness of solid surfaces, we developed a multitude of novel surfaces and strategies. First, we developed metamorphic superomniphobic surfaces that display wetting transition in response to heat. Second, we systematically studied the dynamics of droplets of various liquids during coalescence-induced jumping on textured super-repellent surfaces. Third, we developed a simple and passive strategy consisting of superomniphobic surfaces with a protruding macrotexture to demonstrate coalescence-induced jumping with significantly higher energy conversion efficiency, compared to state-of-the-art surfaces. Fourth, we developed a simple "grafting to" technique to fabricate a novel non-textured hydrophilic surface that is counterintuitively slippery with unprecedented potential to enhance the heat transfer coefficient in dropwise condensation. Fifth, we developed a novel triboelectric-based droplet manipulation technique on smooth hydrophobic slippery surfaces that is very simple without any complex fabrication of manipulation platform or expensive actuation system. Overall, the novel surfaces and strategies developed in this work have significant implications for phase-change heat transfer, liquid transportation, anti-fouling, self-cleaning, drag reduction, corrosion control, and manipulation of liquid droplets.Item Open Access Tuning surface wettability for effective oil-water separation, manipulation of ferrofluid droplets and blood contacting medical devices(Colorado State University. Libraries, 2020) Kantam, Prem, author; Kota, Arun K., advisor; Popat, Ketul C., advisor; Li, Yan, committee memberSurface interaction with liquids have gained a lot of attention that enables us to control wetting properties which find applications in self-cleaning, stain free clothing, non-fouling, separation of liquids etc. In this study we tuned surface wettability of different surfaces to showcase potential applications in oil-water separation, manipulation of under liquid droplets and blood contacting medical devices. First, we designed dual superlyophobic surfaces by combining re-entrant texture and appropriate surface energy with recently discovered recyclable polymer. Dual superlyophobic surfaces display both under-water superoleophobicity and underoil superhydrophobicity. Such surfaces are counter-intuitive because typically underwater superoleophobic surfaces require high surface energy and under-oil superhydrophobic surfaces require low surface energy. We fabricated these surfaces using a simple spray coating method that resulted in textured surface with re-entrant structures. The surface energy of the textured surfaces was then modified through plasma treatment. Our surfaces display under-water superoleophobicity for low surface tension liquids liker oils and under-oil superhydrophobicity for high surface tension liquids like water. We envision that our dual superlyophobic surfaces will find applications in membrane separation, antifouling coatings and droplet-based fluidic devices. Second, we developed polyethylene glycol based hydrophilic slippery surfaces by covalently attaching PEG silane via O-Si bonds to hydroxylated surface to form PEG brushes. The hydrophilic slippery surfaces formed are chemically homogeneous with low molecular weight PEG brushes with high grafting density. These surfaces can easily repel high surface tension liquids like water and blood with a tilt angle of 6°. It is envisioned that these surfaces can be effectively used to reduce protein adsorption, platelet adhesion and bacterial adhesion and the use of slippery surfaces can be an ideal approach for designing surfaces for blood-contacting medical devices.Item Open Access Tuning the interaction of droplets with liquid-repellent surfaces: fundamentals and applications(Colorado State University. Libraries, 2018) Movafaghi, Sanli, author; Kota, Arun K., advisor; James, Susan P., committee member; Henry, Charles S., committee member; Popat, Ketul C., committee memberLiquid-repellent surfaces can be broadly classified as non-textured surfaces (e.g., smooth slippery surfaces on which droplets can slide easily) and textured surfaces (e.g., super-repellent surfaces on which liquid droplets can bead up and roll off easily). The liquid repellency of smooth slippery surfaces can be adjusted by tuning the surface chemistry. The liquid repellency of super-repellent surfaces can be adjusted by tuning the surface chemistry and surface texture. In this work, by systematically tuning the surface chemistry and surface texture and consequently the surface wettability of solid surfaces, the interaction of droplets of various liquids on liquid-repellent surfaces has been investigated. Based on this understanding, the following phenomena/applications have been investigated/developed: (i New methodology to sort liquid droplets based on their surface tension: By tuning the surface chemistry and surface texture of solid surfaces, we tuned the mobility of liquids with different surface tension on super-repellent surfaces. Utilizing this, we fabricated a simple device with precisely tailored domains of surface chemistry that can sort droplets by surface tension. (ii) New approach to detect the quality of fuel blends: By tuning the surface chemistry of solid surfaces, we investigated the interaction of fuel blends with liquid-repellent surfaces. Based on the understanding gained, we fabricated a simple, field-deployable, low-cost device to rapidly detect the quality of fuel blends by sensing their surface tension with significantly improved resolution. (iii) Novel materials with improved hemocompatibility: By systematically tuning the surface chemistry and surface texture and consequently the surface wettability of solid surfaces, we investigated the interaction of blood with super-repellent surfaces. Based on the understanding gained, we fabricated super-repellent surfaces with enhanced hemocompatibility. (iv) Advanced understanding of droplet splitting upon impacting a macroscopic ridge: By systematically tuning the ridge geometry, we investigated the interaction of impacting water droplets with super-repellent ridges. Based on the understanding gained, we demonstrated the scaling law for predicting the height from which water droplets should fall under gravity onto a super-repellent ridge for them to split into two smaller droplets.