Inspired by Stenocara Beetles: From Water Collection to High-Efficiency Water-in-Oil Emulsion Separation

Abstract

Inspired by the water-collecting mechanism of the Stenocara beetle's back structure, we prepared a superhydrophilic bumps-superhydrophobic/superoleophilic stainless steel mesh (SBS-SSM) filter via a facile and environmentally friendly method. Specifically, hydrophilic silica microparticles are assembled on the as-cleaned stainless steel mesh surface, followed by further spin-coating with a fluoropolymer/SiO nanoparticle solution. On the special surface of SBS-SSM, attributed to the steep surface energy gradient, the superhydrophilic bumps (hydrophilic silica microparticles) are able to capture emulsified water droplets and collect water from the emulsion even when their size is smaller than the pore size of the stainless steel mesh. The oil portion of the water-in-oil emulsion therefore permeates through pores of the superhydrophobic/superoleophilic mesh coating freely and gets purified. We demonstrated an oil recovery purity up to 99.95 wt % for surfactant-stabilized water-in-oil emulsions on the biomimetic SBS-SSM filter, which is superior to that of the traditional superhydrophobic/superoleophilic stainless steel mesh (S-SSM) filter lacking the superhydrophilic bump structure. Together with a facile and environmentally friendly coating strategy, this tool shows great application potential for water-in-oil emulsion separation and oil purification.

Under‐Oil Superhydrophilic Poly(vinyl alcohol)/Silica Hybrid Nanofibrous Aerogel for Gravity‐Driven Separation of Surfactant‐Stabilized Water‐in‐Oil Emulsions

“…The demulsification behavior could be attributed to an imbalanced force ( F ib ) on the water droplets, which drove them toward the nanofibers of high surface energy. This force can be described by the following equation:where θ nanofiber and θ oil are the water contact angles on PVA/silica hybrid nanofiber and on the oil surface, respectively. Obviously, θ oil is highly larger than θ nanofiber , due to the fact that the nanofibers are hydrophilic.…”

“…Efficient and green technique for separating water‐in‐oil (W/O) mixtures to obtain the oil with ultrahigh purity is greatly desired, especially in the field of transportation . Tiny amount of water in the oil as transportation fuel can cause serious harm to the engine, the “heart” of transportation vehicles such as airplane, car, and ship, due to the fact that it can condense on the metal surface of the engine to initiate corrosion .…”

“…Similar to oil‐in‐water (O/W) mixtures, W/O mixtures also exist in three types: immiscible W/O mixtures, surfactant‐free W/O emulsions, and surfactant‐stabilized W/O emulsions . Among these three types, the last one is commonly existent in transportation fuels . Since the emulsified water droplets of surfactant‐stabilized W/O emulsions normally have diameters less than 10 µm, they cannot be effectively intercepted by common filters like the metal mesh with special wetting property, whose pore sizes are much larger than their diameters.…”

Recent biomedical applications of bio-sourced materials

“…Inspired by the water-collecting mechanism, Wen et al designed a superhydrophilic bump-superhydrophobic/superoleophilic stainless steel mesh (SBS-SSM) filter using a facile method [ Fig. 1E(c)] [23].…”

Oil–Water Separation Using Superhydrophobic PET Membranes Fabricated Via Simple Dip‐Coating Of PDMS–SiO2 Nanoparticles

“…Due to the growth of the oil industry and the frequency of oil‐spill accidents, the treatment of oil‐contaminated water is an urgent issue in environmental protection . Superhydrophobic and oleophilic membranes (SOMs) can effectively separate the oil from oil–water mixtures by repelling water while letting oil pass through the membrane .…”