PhotoATRP-Based Fluorinated Thermosensitive Block Copolymer for Controllable Water/Oil Separation

Bioinspired design of underwater superoleophobic Poly(N-isopropylacrylamide)/ polyacrylonitrile/TiO2 nanofibrous membranes for highly efficient oil/water separation and photocatalysis

Inspired by fish scales, this study prepares a thermo-responsive underwater oleophobic PNIPAM/PAN/TiO₂ nanofibrous membranes by traditional electrospinning technique using poly-N-isopropylacrylamide (PNIPAM) and polyacrylonitrile (PAN). Thermal properties, mechanical properties, surface chemical composition, wettability, photocatalysis, and oil/water separation of PNIPAM/PAN/TiO₂ membrane are explored compared to pure PNIPAM membrane. Result reveals that PAN/TiO₂ compounds make PNIPAM membrane with a smaller fiber diameter of 141 nm and high tensile stress of 7.4 MPa, and also decompose 98% of rhodamine B after UV light radiation. This bioinspired design structure endows the membrane with superhydrophilicity with a low water contact angle, and underwater superoleophobicity with a high oil contact angle of 157° (petroleum ether) and 151° (dichloromethane). This membrane can efficiency separate oil/water mixture with a high separation efficiency. Moreover, the resultant PNIPAM/PAN/TiO₂ membrane has the bionic fish scale structure, and has wettability respond at lower critical solution temperature making the water flux decreased from 10013 ± 367 L m^-2·h^-1 to 7713 ± 324 L m^-2·h^-1, and thus has a potential to be used in purification of reclaimed water and separation of oil from water.

Role of External Field in Polymerization: Mechanism and Kinetics

The past decades have witnessed an increasing interest in developing advanced polymerization techniques subjected to external fields. Various physical modulations, such as temperature, light, electricity, magnetic field, ultrasound, and microwave irradiation, are noninvasive means, having superb but distinct abilities to regulate polymerizations in terms of process intensification and spatial and temporal controls. Gas as an emerging regulator plays a distinctive role in controlling polymerization and resembles a physical regulator in some cases. This review provides a systematic overview of seven types of external-field-regulated polymerizations, ranging from chain-growth to step-growth polymerization. A detailed account of the relevant mechanism and kinetics is provided to better understand the role of each external field in polymerization. In addition, given the crucial role of modeling and simulation in mechanisms and kinetics investigation, an overview of model construction and typical numerical methods used in this field as well as highlights of the interaction between experiment and simulation toward kinetics in the existing systems are given. At the end, limitations and future perspectives for this field are critically discussed. This state-of-the-art research progress not only provides the fundamental principles underlying external-field-regulated polymerizations but also stimulates new development of advanced polymerization methods.

PP/TiO2 Melt-Blown Membranes for Oil/Water Separation and Photocatalysis: Manufacturing Techniques and Property Evaluations

This study aims to produce polypropylene (PP)/titanium dioxide (TiO₂) melt-blown membranes for oil/water separation and photocatalysis. PP and different contents of TiO₂ are melt-blended to prepare master batches using a single screw extruder. The master batches are then fabricated into PP/TiO₂ melt-blown membranes. The thermal properties of the master batches are analyzed using differential scanning calorimetry and thermogravimetric analysis, and their particle dispersion and melt-blown membrane morphology are evaluated by scanning electron microscopy. TiO₂ loaded on melt-blown membranes is confirmed by X-ray diffraction (XRD). The oil/water separation ability of the melt-blown membranes is evaluated to examine the influence of TiO₂ content. Results show that the thermal stability and photocatalytic effect of the membranes increase with TiO₂ content. TiO₂ shows a good dispersion in the PP membranes. After 3 wt.% TiO₂ addition, crystallinity increases by 6.4%, thermal decomposition temperature increases by 25 °C compared with pure PP membranes. The resultant PP/TiO₂ melt-blown membrane has a good morphology, and better hydrophobicity even in acetone solution or 6 h ultraviolet irradiation, and a high oil flux of about 15,000 L·m⁻²·h⁻¹. Moreover, the membranes have stabilized oil/water separation efficiency after being repeatedly used. The proposed melt-blown membranes are suitable for mass production for separating oil from water in massively industrial dyeing wastewater.

Functionalization of Commercial Sand Core Funnels as Hydrophobic Materials with Novel Physicochemical Properties

A solid surface morphology is of great importance for the fundamental research in the field of hydrophobic materials. Commercial sand core funnels (SCs) are embedded with multilevel pore size and surface roughness, which are excellent models to study the mechanism of surface wettability. This article described a simple, green, and facile method to fabricate hydrophobic surfaces on SCs via reacting with perfluorooctyltriethoxysilane (PFTS) vapor. Systematic analyses on the reaction, properties, and applications of the PFTS-modified SCs were conducted, which involved the reaction time and temperature, water resistance, mechanical durability, self-cleaning test, surface adhesion, and underoil superhydrophobicity. The water contact angle of the modified SCs increased with a decrease of the pore size and an increase of the surface roughness of the sand core particles. The wettability of the modified SCs agrees well with the intermediate states between Wenzel and Cassie-Baxter. The PFTS-modified SCs retained excellent chemical stability in rigid conditions and good mechanical properties. The hydrophobic SCs showed oil/water separation performance with excellent efficiency, reusability, and high flux. Especially for the PFTS-modified SCs with small pore sizes, water-in-oil emulsion separation was successfully realized. The easily accessible, relatively cheap raw materials and facile process in this work are very desirable to obtain a specific wetting surface, which will offer promising applications in various fields.

Phosphate-Based Cross-Linked Polymers from Iodo-ene Photopolymerization: Tuning Surface Wettability through Thiol-ene Chemistry

Motivated by the various reported potential applications of poly(phosphine oxide) materials, a visible light photoinitiated iodo-ene reaction was successfully employed in network polymerization between the phosphorus-containing multifunctional monomer, tris(allyloxymethyl)phosphine oxide (TAOPO), and diiodoperfluorobutane. The cross-linked poly(phosphine oxide) network exhibited a higher glass transition temperature than a similarly cross-linked polymer formulated with trimethylolpropane triallyl ether (TMPTAE). Interestingly, the TMPTAE/DIPFB cross-linked polymer, changed color from clear to yellow within 10 min of exposure to air, whereas the cross-linked poly(phosphine oxide) underwent a similar change only upon heating. Upon investigation, it was determined that alkenes were generated within the polymer network, presumably via elimination, accounting for the observed color. These double bonds, formed in the polymer matrix, permitted surface modification via radical thiol-ene reaction. The successful surface functionalization with PEG-SH resulted in increasing the surface wettability. Additionally, the phosphorus-containing network polymer with double bonds in the polymer matrix showed shape memory capability, this representing an exciting and versatile materials platform.

Thermo-Responsive Cellulose-Based Material with Switchable Wettability for Controllable Oil/Water Separation

A thermo-responsive cellulose-based material (cellulose-g-PNIPAAm) was prepared by grafting N-isopropylacrylamide (NIPAAm) onto bagasse pulp cellulose via Ce (IV)-initiated free radical polymerization. The surfaces of the obtained cellulose-g-PNIPAAm paper showed a rapid wettability conversion from being hydrophilic (water contact angles (WCA) of 0°) at 25 °C to becoming hydrophobic (WCA of 134.2°) at 45 °C. Furthermore, the thermo-responsive mechanism of cellulose-g-PNIPAAm was examined by the in situ variable-temperature 13C NMR, ¹H NMR and AFM analysis. At the same time, the resulting cellulose paper was applied for a switchable separation of oil/water mixtures. Water can pass through the paper under 45 °C, while oil is kept on the paper. When the temperature is above 45 °C, oil can permeate through the paper, while water cannot pass through the water. Moreover, the paper exhibited excellent regeneration performance after five cycles and maintained its switchable wettability.

Rational design of materials interface at nanoscale towards intelligent oil-water separation

Oil-water separation is critical for the water treatment of oily wastewater or oil-spill accidents. The oil contamination in water not only induces severe water pollution but also threatens human beings' health and all living species in the ecological system. To address this challenge, different nanoscale fabrication methods have been applied for endowing biomimetic porous materials, which provide a promising solution for oily-water remediation. In this review, we present the state-of-the-art developments in the rational design of materials interface with special wettability for the intelligent separation of immiscible/emulsified oil-water mixtures. A mechanistic understanding of oil-water separation is firstly described, followed by a summary of separation solutions for traditional oil-water mixtures and special oil-water emulsions enabled by self-amplified wettability due to nanostructures. Guided by the basic theory, the rational design of interfaces of various porous materials at nanoscale with special wettability towards superhydrophobicity-superoleophilicity, superhydrophilicity-superoleophobicity, and superhydrophilicity-underwater superoleophobicity is discussed in detail. Although the above nanoscale fabrication strategies are able to address most of the current challenges, intelligent superwetting materials developed to meet special oil-water separation demands and to further promote the separation efficiency are also reviewed for various special application demands. Finally, challenges and future perspectives in the development of more efficient oil-water separation materials and devices by nanoscale control are provided. It is expected that the biomimetic porous materials with nanoscale interface engineering will overcome the current challenges of oil-water emulsion separation, realizing their practical applications in the near future with continuous efforts in this field.

Thermal and photo-RAFT polymerization of 2,2,2-trifluoroethyl α-fluoroacrylate

RAFT polymerization of 2,2,2-trifluoroethyl α-fluoroacrylate (FATRIFE) was studied under thermal conditions and light irradiation in the presence of four chain transfer agents. Polymers with narrow dispersities were obtained in the presence of trithiocarbonate CTA₂, and this further led to fluorinated block copolymers.

Synthesis of aminopyridine-containing conjugated microporous polymers with excellent superhydrophobicity for oil/water separation

Aminopyridine-containing conjugated microporous polymer based membranes with excellent superhydrophobicity for continuous oil/water separation on a large scale.

Thermoresponsive Melamine Sponges with Switchable Wettability by Interface-Initiated Atom Transfer Radical Polymerization for Oil/Water Separation

Here we have obtained a temperature responsive melamine sponge with a controllable wettability between superhydrophilicity and superhydrophobicity by grafting the octadecyltrichlorosilane and thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) onto the surface of melamine sponge skeletons. The whole process included the silanization in which step the rough surface with low surface energy and the NH₂ were provided, and the atom transfer radical polymerization which ensured the successful grafting of PNIPAAm onto the skeleton's surface. The product exhibits a good reversible switch between superhydrophilicity and superhydrophobicity by changing the temperature below or above the lower critical solution temperature (LCST, about 32 °C) of PNIPAAm, and the modified sponge still retains a good responsiveness after undergoing two temperature switches for 20 cycles. Simultaneously, the functionalized sponges could be used to absorb the oil under water at 37 °C, and they released the absorbed oil in various ways under water at 20 °C, showing wide potential applications including oil/water separation.

Electrospun Fibrous Mat with pH-Switchable Superwettability That Can Separate Layered Oil/Water Mixtures

Oil/water separation has inspired much research interest because of the damages caused to our natural environment due to oily wastewater. As a leader of advanced separation materials, electrospun polymeric fibrous mats having the properties of special surface wettability, high specific surface area, and high porosity will be a good membrane material for the separation of oily wastewater. Herein, we first prepared pH-responsive polymer poly(dimethylsiloxane)-block-poly(4-vinylpyridine) (PDMS-b-P4VP) mat using electrospinning technology. The PDMS-b-P4VP fibrous mat with a thickness of around 250 μm exhibits good pH-switchable oil/water wettability and is able to effectively separate oil or water from layered oil/water mixtures by gravity driven through adjusting the pH value. Stemming from its porous structure and pH-switchable superwettability, the electrospun PDMS-b-P4VP fibrous mat achieved controllable separations with high fluxes of approximately 9000 L h^-1 m^-2 for oil (hexane) and 27 000 L h^-1 m^-2 for water. In addition, extended studies on the polymer/silica nanoparticulate (silica NP) composite fibrous mats show that the addition of an inorganic component improves the thermal stability, pH-switchable wettability, and separation performance of the fibrous mats (approximately 9000 L h^-1 m^-2 for hexane and 32 000 L h^-1 m^-2 for water). It can be concluded from the results that both polymer fibrous mats and silica-filled composite fibrous mats are good candidates for on-demand layered oil/water mixture separation.

Novel Fluorinated Polymers Containing Short Perfluorobutyl Side Chains and Their Super Wetting Performance on Diverse Substrates

Because the emission of perfluorooctanoic acid (PFOA) was completely prohibited in 2015, the widely used poly- and perfluoroalkyl substances with long perfluoroalkyl groups must be substituted by environmentally friendly alternatives. In this study, one kind of potential alternative (i.e., fluorinated polymers with short perfluorobutyl side chains) has been synthesized from the prepared monomers {i.e., (perfluorobutyl)ethyl acrylate (C4A), (perfluorobutyl)ethyl methacrylate (C4MA), 2-[[[[2-(perfluorobutyl)]sulfonyl]methyl]amino]ethyl acrylate (C4SA), and methacrylate (C4SMA)}, and the microstructure, super wetting performance, and applications of the synthesized fluorinated polymers were systematically investigated. The thermal and crystallization behaviors of the fluoropolymer films were characterized by differential scanning calorimetry and wide-angle X-ray diffraction analysis, respectively. Dynamic water-repellent models were constructed. The stable low surface energy and dynamic water- and oil-repellent properties of these synthesized fluorinated polymers with short perfluorobutyl side chains were attributed to the synergetic effect of amorphous fluorinated side chains in perfluoroalkyl acrylate and crystalline hydrocarbon pendant groups in stearyl acrylate. Outstanding water- and oil-repellent properties of fabrics and any other substrates could be achieved by a facile dip-coating treatment using a fluorinated copolymer dispersion. As a result, we believe that our prepared fluorinated copolymers are potential candidates to replace the fluoroalkylated polymers with long perfluorinated chains in nonstick and self-cleaning applications in our daily life.