2013

Vogel N, Belisle RA, Hatton B, Wong TS, Aizenberg J. Transparency and damage tolerance of patternable omniphobic lubricated surfaces based on inverse colloidal monolayers. Nature Communications. 2013;4. Publisher's VersionAbstract
A transparent coating that repels a wide variety of liquids, prevents staining, is capable of self-repair and is robust towards mechanical damage can have a broad technological impact, from solar cell coatings to self-cleaning optical devices. Here we employ colloidal templating to design transparent, nanoporous surface structures. A lubricant can be firmly locked into the structures and, owing to its fluidic nature, forms a defect-free, self-healing interface that eliminates the pinning of a second liquid applied to its surface, leading to efficient liquid repellency, prevention of adsorption of liquid-borne contaminants, and reduction of ice adhesion strength. We further show how this method can be applied to locally pattern the repellent character of the substrate, thus opening opportunities to spatially confine any simple or complex fluids. The coating is highly defect-tolerant due to its interconnected, honeycomb wall structure, and repellency prevails after the application of strong shear forces and mechanical damage. The regularity of the coating allows us to understand and predict the stability or failure of repellency as a function of lubricant layer thickness and defect distribution based on a simple geometric model.
Epstein AK, Hong D, Kim P, Aizenberg J. Biofilm attachment reduction on bioinspired, dynamic, microwrinkling surfaces. New J. Phys. 2013;15 :095018. Publisher's VersionAbstract
Most bacteria live in multicellular communities known as biofilms that are adherent to surfaces in our environment, from sea beds to plumbing systems. Biofilms are often associated with clinical infections, nosocomial deaths and industrial damage such as bio-corrosion and clogging of pipes. As mature biofilms are extremely challenging to eradicate once formed, prevention is advantageous over treatment. However, conventional surface chemistry strategies are either generally transient, due to chemical masking, or toxic, as in the case of leaching marine antifouling paints. Inspired by the nonfouling skins of echinoderms and other marine organisms, which possess highly dynamic surface structures that mechanically frustrate bio-attachment, we have developed and tested a synthetic platform based on both uniaxial mechanical strain and buckling-induced elastomer microtopography. Bacterial biofilm attachment to the dynamic substrates was studied under an array of parameters, including strain amplitude and timescale (1–100 mm s−1), surface wrinkle length scale, bacterial species and cell geometry, and growth time. The optimal conditions for achieving up to  ~ 80% Pseudomonas aeruginosa biofilm reduction after 24 h growth and  ~ 60% reduction after 48 h were combinatorially elucidated to occur at 20% strain amplitude, a timescale of less than  ~ 5 min between strain cycles and a topography length scale corresponding to the cell dimension of  ~ 1 μm. Divergent effects on the attachment of P. aeruginosaStaphylococcus aureus and Escherichia coli biofilms showed that the dynamic substrate also provides a new means of species-specific biofilm inhibition, or inversely, selection for a desired type of bacteria, without reliance on any toxic or transient surface chemical treatments.
Daniel D, Mankin MN, Belisle RA, Wong T-S, Aizenberg J. Lubricant-infused micro/nano-structured surfaces with tunable dynamic omniphobicity at high temperatures. Appl. Phys. Lett. 2013;102 :231603. Full TextAbstract
Omniphobic surfaces that can repel fluids at temperatures higher than 100 °C are rare. Most state-of-the-art liquid-repellent materials are based on the lotus effect, where a thin air layer is maintained throughout micro/nanotextures leading to high mobility of liquids. However, such behavior eventually fails at elevated temperatures when the surface tension of test liquids decreases significantly. Here, we demonstrate a class of lubricant-infused structuredsurfaces that can maintain a robust omniphobic state even for low-surface-tension liquids at temperatures up to at least 200 °C. We also demonstrate how liquid mobility on such surfaces can be tuned by a factor of 1000.
Kim P, Kreder MJ, Alvarenga J, Aizenberg J. Hierarchical or Not? Effect of the Length Scale and Hierarchy of the Surface Roughness on Omniphobicity of Lubricant-Infused Substrates. Nano Lett. 2013;13 (4) :1793-1799. Publisher's VersionAbstract
Lubricant-infused textured solid substrates are gaining remarkable interest as a new class of omni-repellent nonfouling materials and surface coatings. We investigated the effect of the length scale and hierarchy of the surface topography of the underlying substrates on their ability to retain the lubricant under high shear conditions, which is important for maintaining nonwetting properties under application-relevant conditions. By comparing the lubricant loss, contact angle hysteresis, and sliding angles for water and ethanol droplets on flat, microscale, nanoscale, and hierarchically textured surfaces subjected to various spinning rates (from 100 to 10 000 rpm), we show that lubricant-infused textured surfaces with uniform nanofeatures provide the most shear-tolerant liquid-repellent behavior, unlike lotus leaf-inspired superhydrophobic surfaces, which generally favor hierarchical structures for improved pressure stability and low contact angle hysteresis. On the basis of these findings, we present generalized, low-cost, and scalable methods to manufacture uniform or regionally patterned nanotextured coatings on arbitrary materials and complex shapes. After functionalization and lubrication, these coatings show robust, shear-tolerant omniphobic behavior, transparency, and nonfouling properties against highly contaminating media.
Mishchenko L, Aizenberg J, Hatton BD. Spatial Control of Condensation and Freezing on Superhydrophobic Surfaces with Hydrophilic Patches. Adv. Funct. Mater. 2013;23 (36) :4577-4584. Publisher's VersionAbstract
Certain natural organisms use micro‐patterned surface chemistry, or ice‐nucleating species, to control water condensation and ice nucleation for survival under extreme conditions. As an analogy to these biological approaches, it is shown that functionalized, hydrophilic polymers and particles deposited on the tips of superhydrophobic posts induce precise topographical control over water condensation and freezing at the micrometer scale. A bottom‐up deposition process is used to take advantage of the limited contact area of a non‐wetting aqueous solution on a superhydrophobic surface. Hydrophilic polymer deposition on the tips of these geometrical structures allows spatial control over the nucleation, growth, and coalescence of micrometer‐scale water droplets. The hydrophilic tips nucleate water droplets with extremely uniform nucleation and growth rates, uniform sizes, an increased stability against coalescence, and asymmetric droplet morphologies. Control of freezing behavior is also demonstrated via deposition of ice‐nucleating AgI nanoparticles on the tips of these structures. This combination of the hydrophilic polymer and AgI particles on the tips was used to achieve templating of ice nucleation at the micrometer scale. Preliminary results indicate that control over ice crystal size, spatial symmetry, and position might be possible with this method. This type of approach can serve as a platform for systematically analyzing micrometer‐scale condensation and freezing phenomena, and as a model for natural systems.

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