There is a critical need for new energy-efficient solutions to separate oil-water mixtures, especially those stabilized by surfactants. Traditional membrane-based separation technologies are energy-intensive and limited, either by fouling or by the inability of a single membrane to separate all types of oil-water mixtures. Here we report membranes with hygro-responsive surfaces, which are both superhydrophilic and superoleophobic, in air and under water. our membranes can separate, for the first time, a range of different oil-water mixtures in a singleunit operation, with >99.9% separation efficiency, by using the difference in capillary forces acting on the two phases. our separation methodology is solely gravity-driven and consequently is expected to be highly energy-efficient. We anticipate that our separation methodology will have numerous applications, including the clean-up of oil spills, wastewater treatment, fuel purification and the separation of commercially relevant emulsions.

Surfaces that display contact angles 41501 along with low contact angle hysteresis with essentially all high and low surface tension liquids, including water, oils and alcohols, are known as superomniphobic surfaces. Such surfaces have a range of commercial applications, including self-cleaning, non-fouling, stain-free clothing, drag reduction, corrosion prevention and separation of liquids. Such surfaces have thus generated immense academic and industrial interest in recent years. In this review, we discuss the systematic design of superomniphobic surfaces. In particular, we discuss the significance of surface energy, roughness and the critical role of re-entrant texture in obtaining the so-called Cassie-Baxter state with low surface tension liquids. We also discuss how hierarchical scales of texture can yield high contact angles and decrease the contact angle hysteresis of superomniphobic surfaces by reducing the solid-liquid contact area. On the basis of this understanding, we discuss dimensionless design parameters that allow for the systematic design of superomniphobic surfaces. We also review the current literature on superomniphobic surfaces, paying particular attention to surfaces that demonstrate good mechanical, chemical and radiation durability-traits that are essential for any commercial application of superomniphobic surfaces. Finally, we conclude by identifying the unresolved challenges in the fabrication of durable superomniphobic surfaces and highlight the future needs in the field.

In this work, the first-ever membrane-based single unit operation that enables gravity driven, on-demand separation of various oil-water mixtures is developed. Using this methodology, the on-demand separation of free oil and water, oil-in-water emulsions, and water-in-oil emulsions is demonstrated, with ≥99.9% separation efficiency. A scaled-up apparatus to separate larger quantities (several liters) of oil-water emulsions is also developed.

Photoresponsive titania surfaces are of great interest due to their unique wettability change upon ultraviolet light illumination. However, their applications are often limited either by the inability to respond to visible light or the need for special treatment to recover the original wettability. Sensitizing TiO2 surfaces with visible light-absorbing materials has been utilized in photovoltaic applications. Here we demonstrate that a dye-sensitized TiO2 surface can selectively change the wettability towards contacting liquids upon visible light illumination due to a photo-induced voltage across the liquid and the underlying surface. The photo-induced wettability change of our surfaces enables external manipulation of liquid droplet motion upon illumination. We show demulsification of surfactant-stabilized brine-in-oil emulsions via coalescence of brine droplets on our dye-sensitized TiO2 surface upon visible light illumination. We anticipate that our surfaces will have a wide range of applications including microfluidic devices with customizable wettability, solar-driven oil–water clean-up and demulsification technologies.

and HL/OL (omniphilic, all liquids wetting), [ 4 ] have a large number of applications including chemical and biological protection, oil-water separation, stain-resistant textiles, "non-stick" coatings, controlling protein and cell adhesion on surfaces, reduction of biofouling, and enhanced heat transport. However, there is no established technique that allows for selectively generating and patterning all four extreme wettabilities [ 5 ] on a single surface, especially at the length scale necessary for microfl uidic control. In this work, we discuss a facile methodology for the fabrication of surfaces with extreme wettabilities by selectively modifying the surface energy and roughness of different paper surfaces.Paper has recently emerged as a promising materials platform for microfl uidic devices due to its low cost, easy disposal, high surface area, capillary-based wetting, fl exibility, and compatibility with a wide range of patterning and printing techniques. [ 6 ] Since the fi rst report of using paper as a base material in microfl uidics by Whitesides et al. in 2007, [ 7 ] a new era of paper-based microfl uidic devices has arisen. [ 8 ] The ability to pattern wetting/non-wetting channels on paper has allowed multiplexed, small-volume fl uid control both in 2D lateral fl ow on a single surface [ 9 ] and 3D fl ow on stacked layers connected through pores. [ 10 ] Generally, fl uidic channels introduced on paper surfaces are composed of wettable domains bounded by non-wettable domains, or by air gaps. [ 11 ] In most cases, paper-based microfl uidic channels have been developed to contain only water or aqueous solutions. [ 12 ] Few reported techniques used for generating patterned wettability on paper result in devices compatible with even a limited number of non-aqueous liquids. [ 13 ] Further, the wettable channels in the paper-based microfl uidic systems reported thus far show no selective wettability with liquids possessing different surface tensions and/or polarities. In other words, all liquids wet these fl uidic channels. Overall, there is no established technique that allows for the selective generation of all four "extreme wettabilities" [ 5 ] on paper-based microfl uidic channels; that is, the four possible combinations of wetting of oil (oleophilic -OL or oleophobic-OP) and water (hydrophilic-HL and hydrophobic-HP) on a surface. The four extreme wettabilities are: HP/OP (omniphobic, all liquids non-wetting), [ 1 ] HP/OL (water nonwetting, oil wetting), [ 2 ] HL/OP (water wetting, oil

Abstract

Precise control over the geometry and chemistry of multiphasic particles is of significant importance for a wide range of applications. In this work, 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. The synthesis methodology involves the fabrication of a nonwettable surface patterned with monodisperse, wettable domains of different sizes and shapes. When such patterned templates are dip-coated with polymer solutions or particle dispersions, the liquids, and consequently the polymer or the particles, preferentially self-assemble within the wettable domains. Utilizing this phenomenon, we fabricate multiphasic assemblies with precisely controlled geometry and composition through multiple, layered depositions of polymers and/or particles within the patterned domains. Upon releasing these multiphasic assemblies from the template using a sacrificial layer, we obtain multiphasic particles. The templates can then be readily reused (over 20 times in our experiments) for fabricating a new batch of particles, enabling a rapid, inexpensive, and easily reproducible method for large-scale manufacturing of multiphasic particles.

Recently, such membranes with selective wettability (i.e., hydrophilic and in air or underwater oleophobic) have been incorporated with a photocatalytic semiconductor (e.g., TiO 2 , [26] α-Fe 2 O 3 , [27] WO 3 , [28] BiVO 4 , [29] β-FeOOH, [30] g-C 3 N 4 , [31] and Membrane-based technologies are attractive for remediating oily wastewater because they are relatively energy-efficient and are applicable to a wide range of industrial effluents. For complete treatment of oily wastewater, removing dissolved contaminants from the water phase is typically followed by adsorption onto an adsorbent, which complicates the process. Here, an in-air superhydrophilic and underwater superoleophobic membrane-based continuous separation of surfactant-stabilized oil-in-water emulsions and in situ decontamination of water by visible-light-driven photocatalytic degradation of dissolved organic contaminants is reported. The membrane is fabricated by utilizing a thermally sensitized stainless steel mesh coated with visible light absorbing iron-doped titania nanoparticles. Post annealing of the membrane can enhance the adhesion of nanoparticles to the membrane surface by formation of a bridge between them. An apparatus that enables continuous separation of surfactant-stabilized oil-in-water emulsion and in situ photocatalytic degradation of dissolved organic matter in the water-rich permeate upon irradiation of visible light on the membrane surface with greater than 99% photocatalytic degradation is developed. The membrane demonstrates the recovery of its intrinsic water-rich permeate flux upon continuous irradiation of light after being contaminated with oil. Finally, continuous oil−water separation and in situ water decontamination is demonstrated by photocatalytically degrading model toxins in water-rich permeate.