Overview - designing durable surfaces to control matter accretion

Surfaces that control solid, liquid, or vapor accretion have numerous applications, including self-cleaning windows and solar panels; water and fog harvesting; antimicrobial coatings; ice-shedding coatings for airplane wings, automobiles, or wind turbine blades; and enhancing phase-change heat transport during boiling or condensation. The design of such surfaces has been influenced in part by numerous natural surfaces that can direct the accretion of different states of matter. We focus on designing durable surfaces for various matter accretion controls and building coating design principles to provide rational guidance for coating development.

Review articles

Liquid Repellency 

Over the past two decades, surface design approaches in liquid repellency have moved from controlling the wetting of a single high–surface tension liquid, such as water, to other singular but more challenging phases, such as low–surface tension organic liquids. More recently, surfaces have been developed to manifest control over dual-phase mixtures, such as water-oil mixtures, and complex fluids, such as blood. We aim for designing various liquid-repellent coatings to meet different requirements, such as flexibility, transparency, durability, and repellency of both high and low surface tension liquids.

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Membrane Separation

Separation operations are critical across a wide variety of manufacturing industries and account for about one-quarter of all in-plant energy consumption in the United States. Conventional liquid–liquid separation operations require either thermal or chemical treatment, both of which have a large environmental impact and carbon footprint. Consequently, there is a great need to develop sustainable, clean methodologies for separation of miscible liquid mixtures. 

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Ice Shedding

Ice accretion has a negative impact on critical infrastructure, as well as a range of commercial and residential activities. Icephobic surfaces are defined by an ice adhesion strength τice < 100 kPa. However, the passive removal of ice requires much lower values of τice, such as on airplane wings or power lines (τice < 20 kPa). Such low τice values are scarcely reported, and robust coatings that maintain these low values have not been reported previously. We focused on applying different mechanisms to fulfill low ice adhesion, such as interfacial slippery surface, low interfacial toughness, and so on.

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Snow Shedding

The large-scale accretion of snow and ice on surfaces is a well-known risk to structural reliability, creating loads that can collapse roofs, compromise cold weather sensors, bring down power lines,  and jeopardize the aerodynamics of airplane wings.  More recently,  there is growing recognition that photovoltaic (PV) systems in northern latitudes are also at risk from ice and snow loading.  Therefore, developing a surface to facilitate snow shedding becomes a big issue.

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For some applications, ice must be removed before it accretes to an appreciable thickness. For example, even a very thin layer of accreted ice and frost can reduce the heat transfer efficiency of thermal management systems such as condenser coils used in refrigerators, the photovoltaic output of solar panels, and the optical transparency of windshields. Additional energy is required to actively defrost or remove this ice. Hence, there is a need for anti-icing surfaces that possess the ability to delay or suppress the formation or growth of ice. We focus on applying various mechanisms such as polymer brushes to develop durable anti-icing coatings.


Anti-fog or anti-fogging agents and treatments are chemicals that prevent fogging on the surface on which they are applied by inhibiting the condensation of water on the surface. However, most of the agents only provide a temporary anti-fogging effect. A long-lasting and mechanically durable anti-fogging coating is thus needed in various long-term applications. 

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Anti-Bacterial Surfaces

Antifouling and antibacterial surfaces are of extreme interest due to a plethora of potential applications, such as saving lives with medical devices, preventing hospital-acquired infections, and even preventing marine bio-fouling. Currently, there is no durable surface that can completely resist bio-adhesion from a variety of biomolecules for an extended period of time. Thus, a long-lasting anti-microbial coating becomes critical for this application.

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Phase Transition Heat Transfer Enhancement

Due to the combination of latent heat and sensible heat, condensation and boiling are regarded as powerful tactics for heat removal, making them critical characters in energy-related processes. However, there is usually unneglectable energy loss. For example, in energy generation, 85 % of power plants rely on energy cycles including boiling and condensation; in chemical fabrication, the distillation process highly relies on boiling and condensation and contributes 50% of energy cost in the production of various chemicals and fuel. However, the energy efficiency is low (20-40%). Thus, designing a coating to enhance heat transfer is required to reduce energy consumption. 

Polymer and wax Fouling

Surface fouling occurs when undesired matter adheres and accumulates on a surface, resulting in a decrease or loss of functionality. Polymer and wax fouling can cause costly blockages to crude oil pipelines, clog jet fuel injectors, foul chemical reaction vessels, and significantly decrease the efficiency of heat exchangers. Fouling occurs in many forms but can be segmented based on adherent size, modulus, and chemical functionality. Depending on the foulant, surface design strategies can vary greatly. Few strategies exist to prevent the buildup of wax and polymers on surfaces.

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Anti-Marine Fouling

Marine biofouling is a sticky global problem due to the vast diversity of fouling organisms and adhesion mechanisms that hinder a range of maritime applications. Issues associated with marine biofouling include increased fuel consumption from drag,  safety concerns from corrosion,  and attenuation of sensor signals. Challenges specific to the marine environment include the development of robust fouling solutions for a diverse range of biological species and local ocean conditions, toxicity associated with commercial anti-fouling paints, and manufacturing challenges associated with coating a range of materials and non-planar geometries. 

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Drag Reduction in Turbulent Flow

One of the exciting applications of water repellent surfaces is their use for friction drag reduction. About 60% of the fuel consumed by large ships goes directly to overcoming the frictional drag of the water. By coating the side of a ship with a superhydrophobic surface, much of this friction can be avoided.

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Biomedical Applications

Omniphobic Spheroid Platform 

Multicellular spheroids are superior to other culture geometries in reproducing critical physiological conditions of tumors, such as the diffusion of oxygen, nutrients, waste, and drugs, leading to a more precise model of in vivo drug sensitivity and resistance. Previously reported spheroid culture platforms are often difficult to use, expensive, single-use, or mechanically unstable. Here, we report a facile, mechanically stable, high-throughput spheroid culture platform based on hierarchically textured omniphobic surfaces.

Open-channel Microfluidics

Paper has recently emerged as a promising materials platform for microfluidic devices due to its low cost, easy disposal, high surface area, capillary-based wetting, flexibility, and compatibility with a wide range of patterning and printing techniques. We have developed a method of generating omniphobic paper surfaces that are resistant to wetting by a broad range of liquids, including numerous low surface tension solvents, rather than the aqueous systems previously demonstrated.

Wettability Engendered Templated Self-assembly (WETS)

Precise control over the geometry and chemistry of multiphasic particles is of significant importance for a wide range of applications including drug delivery, vaccines and inhalation biotherapeutics, biological sensors, optical devices, and nanomotors. We have developed one of the simplest methodologies for fabricating monodisperse, multiphasic micro- and nanoparticles possessing almost any composition, projected shape, modulus, and dimensions as small as 25 nm.

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