Fabrication of Multifunctional Non-wetting Surfaces and Their Applications for Underwater Bubble Manipulation

DoctorAmong the various surfaces manufactured by applying biomimetic technology, superhydrophobic surface (SHS) and slippery liquid infused porous surfaces (SLIPS) are representative surfaces that mimic the non-wetting properties of the natural organisms. Not only these surfaces dynamically control liquid droplets, but they also manipulate the movement of air bubbles in aqueous media. Thanks to these unique properties, they have been applied to a wide range of applications in underwater gas evolution and adsorption, chemical reactions, drag reduction, pressure sensors, and wastewater treatment and so on. However, their weak mechanical durability is serious obstacle to be applied to the industrial field, so it is inevitable to improve robustness and research the multifunctional properties of non-wetting surfaces. From this point of view, research on improving the mechanical durability of a non-wetting surfaces using an adhesive material has been in the spotlight. Also, when these non-wetting surface are applied to control the movement of underwater gas bubbles, the physical impairment can be minimized, which have a significant effect on key processes in various applications. Herein, the durability of the SHS was increased by using a biocompatible adhesive, and these non-wetting surfaces were grafted to underwater bubble manipulation for practical usages. In chapter 2, we developed a robust and biocompatible superhydrophobic (SH) surface through combinational biomimicking of three natural organisms: lotus leaf, mussel, and sandcastle worm, for the first time. Using the water-immiscible and polycationic characteristics of mussel adhesive protein adhesive (iMglue), a SH iMglue-SiO2(TiO2/SiO2)2 coating was fabricated by solution-based electrical charge-controlled layer-by-layer (ECLbL) growth of nanoparticles (NPs). The fabricated iMglue-SiO2(TiO2/SiO2)2 SH surface showed excellent durable nonwetting properties, and was applied to an intracatheter tube coating to develop antithrombotic catheters under blood flow. Furthermore, we developed a iMglue-employed SH patch for a tissue closure bandage by spraying hydrophobic SiO2 NPs on the iMglue-covered cotton pads. The prepared iMglue-employed SH patch showed perfect bifunctionality with excellent antibiofouling and tissue closure capabilities. In chapter 3, the bubble adhesive force of the SHS and SLIPS were measured, and the phenomenon occurring when these non-wetting surfaces were adopted to the gas evolution electrodes was analyzed. To obtain pure H2 fuel, it is inevitably required to separate the H2/O2 product gas mixture, mainly relying on a membrane system at the current stage. However, this process has inherent durability and cost issues due to contamination, corrosion and its complex configuration. In our current work, we invented a highly compact gas separation and collection method in a water electrolysis system, which is set onto a biomimetically modified electrode without the use of a membrane or external convective flow. A key idea of this smart, compact and self-driven system is gas bubble manipulation by buoyant force and the SLIPS. With the critical help of the biomimetic SLIPS wall by blocking bubble leakage, H2 and O2 product gases can be separately collected at the corresponding collection port. As a result, we achieved a remarkably improved H2 collection value of over 90 % with high purity using this membrane-free electrolysis system in which the product gases are separated only by their intrinsic buoyancy. In chapter 4, a magnetocontrollable lubricant-infused surface (MCLIS) is introduced as a key platform to manipulate underwater bubble motion. To maneuver the motion of bubbles, surface geometry-driven transport has been widely applied by employing asymmetric nonwetting surfaces, which induce Laplace pressure based on the bubble radius differences in confined states. Although this method has successfully demonstrated bubble manipulations in various geometries, it has inevitably shown some critical limitations; gas bubbles move unidirectionally from the tip to the root direction and cease their movements upon reaching unconfined states. This unidirectional and local bubble transport restrains the applicability of the method to many fields, and overcoming this obstacle still remains an enormous challenge. Herein, MCLISs manipulate the adhesion of gas bubbles by controlling magneto-responsive microwire alignments and rendering two reversible adhesion states, sticky (upright) and slippery (laying wires). This unique characteristic of MCLISs enables the bidirectional and geometry-unrestricted transportation of bubbles by the wire geometry-gradient force (Fwgg) generated at sticky-slippery interfaces. Furthermore, our novel magnetic responsive surface supports anti-buoyancy transport and presents promising applications in microreactors and optical laser shutters in aqueous media. In summary, a robust SH iMglue-SiO2(TiO2/SiO2)2 coating was synthesized by solution-based ECLbL growth and iMglue-employed SH patch was fabricated by spray coating method. Thanks to biocompatibility of the iMglue, these unique surfaces applied to various biomedical usages. Also, SLIPS gas wall adopted to gas evolution electrodes for product gas bubble manipulation. Through this, it was possible to separate, transport, and collect the bubbles generated by the hydrogen and oxygen evolution electrodes with bubble adhesive force of SLIPS and buoyancy. Finally, bidirectional and geometry-unrestricted bubble transportation was demonstrated with magnetic responsive wire alignment of the MCLIS