Boosting Demulsification and Antifouling Capacity of Membranes via an Enhanced Piezoelectric Effect for Sustaining Emulsion Separation.

Traditional superwettable membranes for demulsification of oil/water emulsions could not maintain their separation performance for long because of low demulsification capacity and surface fouling during practical applications. A charging membrane could repel the contaminants for a while, the charge of which would gradually be neutralized during the separation progress. Here, a superhydrophilic piezoelectric membrane (SPM) with sustained demulsification and antifouling capacity is proposed for achieving prolonged emulsion separation, which is capable of converting inherent pulse hydraulic filtration pressure into pulse voltage. A pulse voltage up to -7.6 V is generated to intercept the oil by expediting the deformation and coalescence of emulsified oil droplets, realizing the demulsification. Furthermore, it repels negatively charged oil droplets, avoiding membrane fouling. Additionally, any organic foulants adhering to the membrane undergo degradation facilitated by the generated reactive oxygen species. The separation data demonstrate a 98.85% efficiency with a flux decline ratio below 14% during a 2 h separation duration and a nearly 100% flux recovery of SPM. This research opens new avenues in membrane separation, environmental remediation, etc.

Designing Robust Superhydrophobic Materials for Inhibiting Nucleation of Clathrate Hydrates by Imitating Glass Sponges.

Superhydrophobic surfaces are suggested to deal with hydrate blockage because they can greatly reduce adhesion with the formed hydrates. However, they may promote the formation of fresh hydrate nuclei by inducing an orderly arrangement of water molecules, further aggravating hydrate blockage and meanwhile suffering from their fragile surfaces. Here, inspired by glass sponges, we report a robust anti-hydrate-nucleation superhydrophobic three-dimensional (3D) porous skeleton, perfectly resolving the conflict between inhibiting hydrate nucleation and superhydrophobicity. The high specific area of the 3D porous skeleton ensures an increase in terminal hydroxyl (inhibitory groups) content without damaging the superhydrophobicity, achieving the inhibition to fresh hydrates and antiadhesion to formed hydrates. Molecular dynamics simulation results indicate that terminal hydroxyls on a superhydrophobic surface can inhibit the formation of hydrate cages by disordering the arrangement of water molecules. And experimental data prove that the induction time of hydrate formation was prolonged by 84.4% and the hydrate adhesive force was reduced by 98.7%. Furthermore, this porous skeleton still maintains excellent inhibition and antiadhesion properties even after erosion for 4 h at 1500 rpm. Therefore, this research paves the way toward developing novel materials applied in the oil and gas industry, carbon capture and storage, etc.

A superwetting stainless steel mesh with Janus surface charges for efficient emulsion separation.

Design of charged materials for demulsification of ionic surfactant-stabilized oil-in-water emulsions is emerging in recent years. Herein, a superwetting stainless steel mesh with Janus surface charges (Janus SSM) was prepared by respectively brush-coating polyethyleneimine/aminated carbon nanotubes (PEI/CNTs-NH2) coating and polyacrylic acid (PAA) coating on its two sides. Two demulsification mechanisms, i.e., electrostatic attraction-repulsion and electrostatic repulsion-attraction based on the synergism of two oppositely charged sides were proposed. Combined with the superwettability and optimized pore size, the Janus SSM can successfully be used to demulsify, coalesce and separate emulsions. In detail, the Janus SSM exhibited separation efficiencies of up to 99.29%, 97.12% for SDS- and DTAC-stabilized oil-in-water emulsions respectively under the electrostatic attraction-repulsion mechanism, and up to 97.10%, 98.57% under the electrostatic repulsion-attraction mechanism. The results indicated that the electrostatic attraction-repulsion mechanism proposed in this study is conductive to achieving higher efficiency in emulsion separation. Furthermore, excellent durability extend the operation life of Janus SSM. This Janus SSM, which combines opposite charges on its two sides, may advance the development of charged materials for emulsion separation.

Janus sand filter with excellent demulsification ability in separation of surfactant-stabilized oil/water emulsions: An experimental and molecular dynamics simulation study.

Developing efficient separation materials for surfactant-stabilized oil/water emulsions is of great importance while significantly challenging. In this work, a sand filter with Janus channels was prepared by simply mixing superhydrophilic and superhydrophobic quartz sand in a mass ratio of 1:1. Due to the imbalanced force of droplets in those Janus channels, better separation performance under gravity was achieved for both surfactant-stabilized oil-in-water and water-in-oil emulsions than the superhydrophilic or superhydrophobic sand filter alone. It also received high flux (1080.13 L m-2 h-1 for dichloroethane-in-water emulsion and 1378.07 L m-2 h-1 for water-in-dichloroethane emulsion) and high separation efficiency (99.80% for dichloroethane-in-water emulsion and 99.98% for water-in-dichloroethane emulsion). Molecular dynamics based computational work and experimental studies revealed that the Janus channels of mixed sand layer exhibited greater interaction energy with emulsion droplets for more efficient adsorption, resulting in better demulsification capability and separation performance. The as-prepared Janus sand filters retained excellent separation performance after 50 cycles of the stability test. Together with the needs on only cheap and easily accessible raw materials and its environmentally friendly preparation method, this Janus sand filtration process exhibits its great potential for the separation of surfactant-stabilized oil/water emulsions.

Enhanced Movement of Two-Component Droplets on a Wedge-Shaped Ag/Cu Surface by a Wettability Gradient.

The wedge-shaped Ag/Cu surface with a contact angle (CA) [droplet of 30 vol % propylene glycol (PG)] of 18.6° in the wedge track and 64.6° at its periphery was fabricated through a facile gradient displacement reaction on the Cu substrate. The aqueous droplet of 30% PG could realize directed motion on the wedge track without back-end pinning, moving in a two-stage process of front-end spreading and subsequent back-end shrinking. A wettability gradient from 64.6 to 18.6° on the wedge surface could enhance the droplet motion, especially during the second stage. A favorable length of the wettability gradient (15 mm) was obtained, capable of moving the droplet the farthest displacement of 21.6 mm at a velocity of 0.53 mm/s on a wedge track with the wedge angle of α = 10° and length of 25 mm. The driving force arising from the wettability gradient during the second stage was evaluated theoretically to elucidate the effect of the length of the wettability gradient on the movement. Finally, three T-shaped self-driven surface micromixers composed of a mixing zone with uniform wettability and a transportation zone with different gradients were designed to test the drainage ability of droplets away from the surface. The wedge track combined with the wettability gradient was found to be capable of removing the mixed droplet completely out of the mixing region and flowing away, while the droplet would attach or stay in the mixing zone if actuated by the shape gradient or the wettability gradient alone.

A durable superwetting clusters-inlayed mesh with high efficiency and flux for emulsion separation.

How to rapidly and efficiently separate surfactant-stabilized emulsions has been a great challenge for oil/water separation materials. In this work, a durable superwetting copper mesh with high efficiency and flux for gravity-driven emulsion separation was fabricated by subtly inlaying polydopamine/polyethyleneimine@aminated carbon nanotubes (PDA/PEI@CNTs-NH2) clusters in the mesh pores. The porous clusters with abundant cationic groups render the mesh with superwettability, submicron permeation channels and positive charges, so as to achieve strong demulsification ability. Based on the superwettability and the strong demulsification ability, the PDA/PEI@CNTs-NH2 clusters-inlayed copper mesh (PPC-CM) exhibited high separation efficiency of over 99.5% for various anionic surfactant-stabilized oil-in-water emulsions. Meanwhile, the permeation flux of PPC-CM solely driven by gravity is as high as 3946.3 L m-2 h-1. The strong demulsification ability and high permeation flux of the superwetting mesh are due to the synergistic action of charge-screening effect of -NH3+ and size-sieving effect of optimized pore size. Furthermore, the resultant mesh exhibited excellent durability that it could resist serious physical abrasion and chemical corrosion. Especially the mesh after repeated separation can recover its positive charge by a simple acid treatment. These excellent performances highlight the superwetting mesh a promising potential for sustainable separation of highly stabilized oil/water emulsions.

Facile fabrication of an F-POSS polymer-based liquid-repellent Cu mesh with excellent durability and self-cleaning performance.

A facile method that combines alkali-assisted oxidation and -SH chelation with a click chemistry reaction was employed to create an F-POSS polymer surface (fluorinated octavinyl polyhedral oligomeric silsesquioxane polymer)-based Cu mesh (F-POSS-OM). The as-prepared F-POSS-OM surface displayed a cohering hierarchical nano-F-POSS polymer granule/micro-Cu(OH)2 wire structure, which provided a re-entrant geometry needed for liquid-repellency and low liquid sliding angles (<15°). Moreover, the easy-prepared structure endows the F-POSS-OM with remarkable durability for mechanical and chemical damages, including wear abrasion, tape-peeling, 100 cm-height hammer impact, severe hand twisting, strong acid/base/salt solutions, and high temperatures. Importantly, F-POSS-OM still retained excellent self-cleaning performance even after being subjected to these damages.

Allylated chitosan-poly(N-isopropylacrylamide) hydrogel based on a functionalized double network for controlled drug release.

Smart hydrogels with dual network were presented since a new allylated chitosan was conceived. As a double network hydrogel, its first network consisted of poly(N-isopropylacrylamide) worked as the gel matrix, and its second network with Schiff base bond enabled itself function as a molecular switch through the formation and break of the bond. When only the intestinal fluid was used, the second network could provide efficient protection for the loaded drug, and the drug release mechanism conformed to the non-Fickian type diffusion. While pre-treated with simulated gastric fluid, the switch would be opened and the mechanism was the Fickian type, which increased the cumulative percentage of drug release by about 25% and the release time by about 300 min. Besides, the hydrogel was characterized by 1H NMR, FT-IR and SEM. The effects of allylated chitosan, pH and crosslinker on the swelling ratio and morphology of hydrogel were also studied.

Ca2+, redox, and thermoresponsive supramolecular hydrogel with programmed quadruple shape memory effect.

A new shape memory hydrogel, which can be programmed with quadruple geometries when stimuli are applied sequentially, is presented. With a new redox-responsive stimulus coupled with two other common regulation mechanisms, this hydrogel shows multiple shape memory behaviours, which is promising for various applications, especially drug delivery.

Synthesis and self-assembly behavior of polyhedral oligomeric silsesquioxane-based triblock copolymers in selective solvents by dissipative particle dynamics simulation.

A polyhedral oligomeric silsesquioxane (POSS)-based hybrid triblock copolymer - methyl methacrylate-b-perfluoroalkylethyl methacrylate-b-methacrylisobutyl polyhedral oligomeric silsesquioxane (PMMA-b-PFMA-b-PMAPOSS) was synthesized via an atom transfer radical polymerization (ATRP) method. The self-assembly behavior of triblock copolymers in selective solvents of tetrahydrofuran (THF) and trichlorotrifluoroethane (F113) was studied using dissipative particle dynamics (DPD) simulation. The effects of the block sequence and volume ratio of F113/THF were discussed. The aggregate morphology and size were also characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS). The simulation results showed that the spherical micelle with core-shell-corona or core-mixed shell structure could be formed and the micelle size increased with the F113 content, which was in qualitative agreement with the experimental results. The DPD simulation revealed the dynamic process of the formation of aggregates at the mesoscopic scale, which can be considered as an adjunct to experiments and provides other valuable information for the experiments.

Droplet Motion on a Shape Gradient Surface.

We demonstrate a facile method to induce water droplet motion on an wedge-shaped superhydrophobic copper surface combining with a poly(dimethylsiloxane) (PDMS) oil layer on it. The unbalanced interfacial tension from the shape gradient offers the actuating force. The superhydrophobicity critically eliminates the droplet contact line pinning and the slippery PDMS oil layer lubricates the droplet motion, which makes the droplet move easily. The maximum velocity and furthest position of droplet motion were recorded and found to be influenced by the gradient angle. The mechanism of droplet motion on the shape gradient surface is systematically discussed, and the theoretical model analysis is well matched with the experimental results.

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

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/SiO2 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.

Thermal properties and crystallite morphology of nylon 66 modified with a novel biphenyl aromatic liquid crystalline epoxy resin.

In order to improve the thermal properties of important engineering plastics, a novel kind of liquid crystalline epoxy resin (LCER), 3,3',5,5' -Tetramethylbiphenyl-4,4' -diyl bis(4-(oxiran-2-ylmethoxy)benzoate) (M1) was introduced to blend with nylon 66 (M2) at high temperature. The effects of M1 on chemical modification and crystallite morphology of M2 were investigated by rheometry, thermo gravimetric analysis (TGA), dynamic differential scanning calorimetry (DSC) and polarized optical microscopy (POM). TGA results showed that the initial decomposition temperature of M2 increased by about 8 °C by adding 7% wt M1, indicating the improvement of thermal stability. DSC results illustrated that the melting point of composites decreased by 12 °C compared to M2 as the content of M1 increased, showing the improvement of processing property. POM measurements confirmed that dimension of nylon-66 spherulites and crystallization region decreased because of the addition of liquid crystalline epoxy M1.

Synthesis and dissipative particle dynamics simulation of cross-linkable fluorinated diblock copolymers: self-assembly aggregation behavior in different solvents.

Developing microstructures, such as low molecular aggregates, spherical micelles and multi-compartment micelles, is an expanding area of research in Materials Science. By applying an atom transfer radical polymerization (ATRP) process to cross-linkable fluorinated diblock copolymers and analyzing the data we are able to demonstrate the potential for developing films with different micro-structures for additional biological research. Applying the Dissipative Particle Dynamic (DPD) Method, Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) techniques to cross-linkable fluorinated diblock copolymers of (methyl methacrylate-co-hydroxyethyl methacrylate-co-butyl methacrylate)-b-2-(perfluoroalkyl)ethyl methacrylate (MMA-co-HEMA-co-BMA-b-FMA) we were able to analyze the structures and their relationships to the aggregation of various microstructure formations through the use of various solvents in the process. For the self-assembly of the cross-linkable diblock copolymer in solutions, the DPD simulation results are only in qualitative agreement with experimental data of aggregate morphologies and sizes. This suggests an improved approach to creating materials and methods necessary for studying microstructures in films used in other research areas. Our work examines whether using selective solvents can be easily extended to prepare aggregates with different morphologies, which is an effective shortcut to obtain films with different microstructures. DPD simulation can be considered as an adjunct to experiments and provides other valuable information for the experiment.

Synthesis of composite particles through emulsion polymerization based on silica/fluoroacrylate-siloxane using anionic reactive and nonionic surfactants.

The composite particles with core/shell structure resulting from the combination of silica seed and hydrophobic copolymer (dodecafluoroheptyl methacrylate (DFMA), gamma-methacryloxypropyltriisopropoxidesilane (MAPTIPS), methyl methacrylate, butyl acrylate) were synthesized by emulsion polymerization. The amount of the silica seeds, concentration of reactive surfactant, as well as the addition of DFMA and MAPTIPS, have strong influences on the morphology of composite particles. It has been shown that it would be possible to produce stable organic/inorganic composite particles with inhomogeneous core/shell structure encapsulated by hydrophobic fluorinated acrylate even though using unmodified silica particles and admixture of anionic and nonionic surfactants. However, there was an obvious difference on the morphologies of core-shell structure whether the DFMA and MAPTIPS were added or not. It was concluded that two kinds of polymerization approaches might coexist in the presence of DFMA and MAPTIPS for raw silica. One clear advantage of this process is that there is only one silica bead for each composite particle. This kind of stable core-shell structural hybrid latex is useful for preparing high performance hydrophobic coating.