Designing Robust Liquid and Solid Repellent Surfaces

[摘要] Surfaces that remain uncontaminated by liquids and solids have been investigated over the last two decades to address numerous disparate engineering challenges. The applications for such materials include: self-cleaning surfaces, drag-reducing coatings for ships, fog-resistant windows, efficient heat exchangers, ice-shedding wind turbines and powerlines, membranes that allow for facile clean- up of oil spills, and inexpensive microfluidic diagnostic devices. Researchers have employed a multitude of approaches, such as textured porous solids that entrap air, lubricant-infused surfaces, covalently attached monolayers, or compliant elastomers, to effectively repel high- and low-surface-tension liquids, including water, oils, and solvents, as well as undesired solid materials, including ice, dirt, and minerals. However, the limited longevity of these surfaces has impeded their widespread usage. Damaging environmental conditions, such as mechanical abrasion, elevated temperature, ultraviolet light, harsh solvents, extended immersion under elevated liquid pressure, and micro-organisms, can all rapidly degrade the functionality of these materials in the real world. This dissertation presents the systematic design of liquid- and solid-repellent surfaces with improved resistance to these damaging conditions, and explores some of their applications. The first research chapter outlines a novel fabrication methodology for hyperbranched, hierarchical nanowire structures with independently controllable geometry at each length scale. This novel process was utilized for the fabrication of superomniphobic surfaces with low adhesion to very low-surface-tension liquids, such as heptane. These surfaces also demonstrated high resistance to wetting under pressure. The next three chapters discuss the systematic design of repellent surfaces which are more scalable, and resist a broader range of damaging conditions. The first demonstrates the methodical identification of spray-coating formulations that produce mechanically robust and thermally healable superhydrophobic surfaces, based on the optimization of partial miscibility between hydrophobic small molecules and polymer matrices. These coatings far exceeded the durability of commercial superhydrophobic coatings, and are being adapted for marine drag reduction applications. Though exceptionally durable, the superhydrophobic coatings were not capable of repelling low-surface-tension liquids (i.e., not ;;superomniphobic”) and were not transparent. To address these limitations and improve on the limited lifetime of existing superomniphobic or omniphobic surfaces, a smooth, transparent, substrate-independent ;;omniphobic” coating was also developed. Optimization of phase-separation was used again to maximize the repellency and abrasion resistance of the coatings. Lastly, covalently-attached polydimethylsiloxane thin films, deposited using a fast and facile vapor-phase methodology, were shown to repel even ultra-low-surface-tension fluorinated liquids, as well as a variety of solids, including marine algae. These films exhibited high liquid mobility and low solid adhesion forces due to their liquid-like, flexible, nature. Due to their thermal stability and conductivity, these films are promising for heat-transfer applications, particularly for facilitating efficient drop-wise condensation of low-surface-tension solvents, which has not been extensively studied. The following three chapters discuss inexpensive open-channel microfluidic devices fabricated from pressure-resistant superomniphobic fluorinated paper or superhydrophobic/oleophobic textured silicon. These devices even confined fast-flowing low-surface-tension liquids, such as hexane. This enabled the first demonstration, in open-channel devices, of the chemical lysis and detection of E. coli bacteria and the fabrication of hydrophilic or hydrophobic polymer microparticles via flow-focusing emulsification. The final chapter reports novel superhydrophobic cell-culture vessels that readily generated spheroidal cancer cell colonies for in vitro biological studies and therapeutic assays. This methodology improved accuracy over conventional two-dimensional culture techniques, while providing greater stability than state-of-the-art hanging drop plates.

[发布机构] University of Michigan

[效力级别] non-wetting surfaces

[关键词] superhydrophobic and superomniphobic surfaces;non-wetting surfaces;low adhesion surfaces;anti-fouling surfaces;open-channel microfluidics;marine drag reduction;Materials Science and Engineering;Engineering;Macromolecular Science & Engineering