Design and Applications of Surfaces for Solid Fouling Control

Be it the bacterial/viral settlement on doorknobs or the adhesion of ice on car windshields, the unwanted attachment of solid contaminants on surfaces in our environment can present a significant economic and societal burden. Surfaces that are able to resist or shed solids can find applications in the de-icing of airplane wings, preventing marine fouling of ship hulls, eradicating bacterial and viral contamination within hospitals, controlling wax and asphaltene accumulation within crude oil pipelines, and inhibiting scale and frost formation on heat exchanger surfaces. These endless applications encompass foulants which can possess a wide range of moduli (few Pa to few GPa), length scales (few nm2 to several m2) and modes of adhesion. In this work, surface design strategies against a broad range of inorganic and biological foulants will be discussed including ice, frost, snow, Gram-positive and Gram-negative bacteria, and SARS-CoV-2 (the virus responsible for the ongoing COVID-19 pandemic). Performance over application areas ranging from a few μm2 to several m2 will be displayed with a focus on application-oriented testing, scalability and longevity. This work introduces ice as a model foulant and discuss strategies to minimize the forces required to release ice from different surfaces. In Chapter 2, a novel class of de-icing materials are introduced that exhibit a low interfacial toughness (LIT) with ice, resulting in systems for which the forces required to remove large areas of ice (a few square centimeters or greater) are both low and independent of the iced area. Chapter 3 further shows that these LIT coatings can be used to facilitate shedding of snow, a foulant which can possess a wide range of physical properties. Chapter 4 then transitions into controlling the nucleation and growth of ice/frost on a surface introducing a new class of surfaces that is both anti-icing and icephobic. Chapter 5 introduces the world of biological fouling where we describe a new class of solid surfaces based on naturally occurring antimicrobial molecules which are capable of rapid disinfection (>3-log reduction within few minutes) of a variety of current and emerging pathogens while maintaining persistent efficacy over several months and under extreme environmental duress. We show that these surfaces possess broad spectrum antimicrobial efficacy against E. coli, MRSA, P. aeruginosa and SARS-CoV-2, concluding with their application in burn wound dressings, in vitro and in vivo. Overall, this work highlights the design of state-of-the-art surfaces at the forefront of their field and dives into their performance under different application environments. These patented surfaces have already attracted interest in industry for various residential, transportation, healthcare, renewable energy, military and naval applications.PHDMacromolecular Science & EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/169866/1/adhyani_1.pd

Rational Design of Transparent Nanowire Architectures with Tunable Geometries for Preventing Marine Fouling

Marine biofouling is a sticky global problem that hinders maritime industries. Various microscale surface structures inspired by marine biological species have been explored for their anti- fouling properties. However, systematic studies of anti- marine- fouling performance on surface architectures with characteristic length- scales spanning from below 100 nm to greater than 10 µm are generally lacking. Herein, a study on the rational design and fabrication of ZnO/Al2O3 core- shell nanowire architectures with tunable geometries (length, spacing, and branching) and surface chemistry is presented. The ability of the nanowires to significantly delay or prevent marine biofouling is demonstrated. Compared to planar surfaces, hydrophilic nanowires can reduce fouling coverage by up to - 60% after 20 days. The fouling reduction mechanism is mainly due to two geometric effects: reduced effective settlement area and mechanical cell penetration. Additionally, superhydrophobic nanowires can completely prevent marine biofouling for up to 22 days. The nanowire surfaces are transparent across the visible spectrum, making them applicable to windows and oceanographic sensors. Through the rational control of surface nano- architectures, the coupled relationships between wettability, transparency, and anti- biofouling performance are identified. It is envisioned that the insights gained from the work can be used to systematically design surfaces that reduce marine biofouling in various industrial settings.Core- shell nanowire architectures with tunable geometries (length, spacing, and branching) and surface chemistry are shown to significantly delay marine biofouling. The fouling reduction mechanism is mainly due to the two effects: reduced effective settlement area and mechanical biocide. The insights gained from the work can be used to systematically design surfaces that reduce marine biofouling in various industrial settings.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/162819/3/admi202000672-sup-0001-SuppMat.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/162819/2/admi202000672_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/162819/1/admi202000672.pd

Facilitating Large-Scale Snow Shedding from In-Field Solar Arrays using Icephobic Surfaces with Low-Interfacial Toughness

Large-scale accrual of snow and ice on solar arrays in northern latitudes can cause significant power generation losses during winter. Depending on environmental conditions, snow can encompass a wide range in physical characteristics from dry snow (modulus ≈100 kPa and density ≈0.1 g cm−3) to bulk ice (modulus ≈8 GPa and density ≈0.9 g cm−3). This variation in snow morphology has made the development of a passive, broad-spectrum, snow and ice-shedding surface challenging. Here, the authors develop one of the first surfaces that simultaneously possesses both low-interfacial strength (τ˄ice < 50 kPa) and toughness (Γice < 0.5 J m−2) with ice. These surfaces, fabricated via the addition of mobile polymer chains/oils to a thin polymeric coating, require extremely low detachment forces for ice, enabling its passive shedding at virtually any accretion length scale. Preliminary evidence that the new surfaces can shed different forms of snow and ice from field-deployed solar arrays, over a range of subzero temperatures for several weeks, leading to significant increases in power generation is provided. The optically transparent surfaces are easily scalable and can be widely deployed by the solar industry in areas that see persistent snow. Other applications include automotive windshields, LIDAR covers for autonomous vehicles, and cold climate optical sensors.Coatings that simultaneously possess both low-interfacial strength and toughness with ice are developed. These surfaces can shed different forms of snow and ice from field-deployed solar arrays, over a range of subzero temperatures for several weeks, leading to significant increases in power generation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/172801/1/admt202101032-sup-0001-SuppMat.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/172801/2/admt202101032.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/172801/3/admt202101032_am.pd