Poly(N,N-diethylacrylamide)-endowed spontaneous emulsification during the breath figure process and the formation of membranes with hierarchical pores.

The spontaneous emulsification for the formation of water-in-oil (W/O) or oil-in-water (O/W) emulsions needs the help of at least one kind of the third component (surfactant or cosolvent) to stabilize the oil-water interface. Herein, with the water/CS2-soluble polymer poly(N,N-diethylacrylamide) (PDEAM) as a surfactant, the spontaneous formation of water-in-PDEAM/CS2 emulsions is reported for the first time. The strong affinity between PDEAM and water or the increase of PDEAM concentration will accelerate the emulsification process with high dispersed phase content. It is demonstrated that the spontaneous emulsification of condensed water droplets into the PDEAM/CS2 solution occurs during the breath figure process, resulting in porous films with two levels of pore sizes (i.e., micron and submicron). The emulsification degree and the amounts of submicron-sized pores increase with PDEAM concentration and solidifying time of the solution. This work brings about incremental interest in spontaneous emulsification that may happen during the breath figure process. The combination of these two simultaneous processes provides us with an option to build hierarchically porous structures with condensed and emulsified water droplets as templates. Such porous membranes may have great potential in fields such as separation, cell culture, and biosensing.

Self-Flipping Solar Seesaw Evaporators Leverage Scaling to De-Scale.

Salt scaling poses a significant obstacle to the practical implementation of solar-driven evaporation for desalination. Attempts to mitigate scaling by enhancing mass transfer often lead to a compromise in evaporation efficiency due to associated heat loss. In the present work, a novel seesaw evaporator with a Janus structure to harness scaling for periodic self-descaling is reported. The seesaw evaporators are facilely fabricated by delignifying balsa wood and subsequently single-sided spray-coating it with soot and polydimethylsiloxane (PDMS). This unique Janus structure enables the evaporator to float on the brine while ensuring an ample supply of solution for evaporation. During evaporation, salt ions are transported directionally toward the cocked end of the evaporator to form scaling, triggering the seesaw evaporator to flip once a threshold is reached. The accumulated salts re-dissolve back into the solution. By adjusting the tilt angle, the evaporator can achieve an impressive evaporation rate of up to 2.65 kg m-2  h-1 when evaporating an 8 wt.% NaCl solution. Remarkably, these evaporators maintain a stable evaporation rate during prolonged 120 h operation and produce ≈3.93-6.35 L m⁻2 ·day⁻¹ of freshwater from simulated brines when assembled into an evaporation device.

Polystyrenes with both hydrophilic and hydrophobic moieties: synthesis and self-assembly behaviors.

Fluorinated polymers are emerging as important alternatives for isoporous film fabrication by the breath figure technique, originating from the special characteristics endowed by fluorine elements such as low surface energy and good chemical stability. In this work, we design and synthesize polystyrenes (∼3600 Da) with perfluoroalkyl groups (-C3F7 or -C7F15) at both chain ends and hydrophilic oligo(ethylene glycol) units ((C2H4O)n, n = 1/2/3) in the chain middle by taking advantage of the bifunctional atom transfer radical polymerization (ATRP) initiators and post-substitution of the terminal bromine. We investigate the influence of the two disparate groups on the physical characteristics of the polymers and self-assembly behaviors during the dynamic breath figure process. It shows that the elongation of hydrophilic segments can greatly decrease the interfacial tension between the polymer solution and water (from 41.8 to 37.4 mN m-1), and the functionalization with perfluoroalkyl end groups diminishes the ability of the polymers to precipitate at the interface, as demonstrated by the cloud point results. Studies of the morphology of the porous films suggest that both low interfacial tension and strong capability of interfacial precipitation are beneficial to droplet stabilization and honeycomb pattern formation at low solution concentrations.

Rapid Immobilization of Silver Nanoparticles via Amino-quinone Coatings Enables Surface-Enhanced Raman Scattering Detection.

Immobilization of metal nanoparticles (NPs) on flexible substrates for surface-enhanced Raman scattering (SERS) has received great attention. Anchoring NPs on substrates generally involves the process of surface modification, thanks to its simple, universal, and nondestructive features. 2-Hydroxy-1,4-naphthoquinone (HNQ), a plant-derived compound used to dye hairs and nails, may interact with polyamine or metal ions to form a surface coating. Here, we report the formation of amino-quinone coatings via the co-deposition of HNQ and polyethyleneimine, which provides a functionalized platform to rapidly immobilize Ag NPs on substrates such as a poly(dimethylsiloxane) (PDMS) film to fabricate Ag-PDMS substrates for SERS detection. The detection concentrations are down to 10-8 M for rhodamine 6G. This work expands the system of surface co-deposition and further provides a facile route to prepare a highly efficient SERS substrate.

Less-Ordered Hydration Shell around Poly(N,N-diethylacrylamide) Is Insensitive to the Clouding Transition.

Raman multivariate curve resolution (Raman-MCR) is applied to examine how the hydration shell around poly(N,N-diethylacrylamide) (PDEAM) changes upon heating, in comparison with poly(N-isopropylacrylamide) (PNIPAM), both of which undergo a clouding transition near room temperature. We report that PDEAM possesses a less-ordered and smaller hydration shell than PNIPAM. Furthermore, the PDEAM hydration-shell structure is insensitive to the occurrence of clouding, indicating the coil-globule transition and aggregation of multiple chains can be achieved without the hydration-shell structural transformation.

Surface Coatings via the Assembly of Metal-Monophenolic Networks.

Mussel-inspired surface modification has received significant interest in recent years because of its simplicity and versatility. The deposition systems are still mainly limited to molecules with catechol chemical structures. In this paper, we report a novel deposition system based on a monophenol, vanillic acid (4-hydroxy-3-methoxybenzoic acid), to fabricate metal-phenolic network coatings on various substrates. The results of the water contact angle and zeta potential reveal that the modified polypropylene microfiltration membrane is underwater superhydrophobic and positively charged, showing applications in oil/water separation and dye removal. Furthermore, the single-face modified Janus membrane is promising in switchable oil/water separation. The results demonstrate a novel example of the metal-monophenolic deposition system, which expands the toolbox of surface coatings and facilitates the understanding of the deposition of phenols.

Engineered Coatings via the Assembly of Amino-Quinone Networks.

Engineering coatings with precise physicochemical properties allows for control over the interface of a material and its interactions with the surrounding environment. However, assembling coatings with well-defined properties on different material classes remains a challenge. Herein, we report a co-assembly strategy to precisely control the structure and properties (e.g., thickness, adhesion, wettability, and zeta potential) of coatings on various materials (27 substrates examined) using quinone and polyamine building blocks. By increasing the length of the amine building blocks from small molecule diamines to branched amine polymers, we tune the properties of the films, including the thickness (from ca. 5 to ca. 50 nm), interfacial adhesion (0.05 to 5.54 nN), water contact angle (130 to 40°), and zeta potential (-42 to 28 mV). The films can be post-functionalized through the in situ formation of diverse nanostructures, including nanoparticles, nanorods, and nanocrystals. Our approach provides a platform for the rational design of engineered, substrate-independent coatings for various applications.

Surface Metallization of Porous Polymer Materials for Multifunctional Applications.

Porous materials have attracted great interest in recent years, and a variety of surface modification methods have been developed to endow porous materials with multifunctional applications. Herein, multifunctional porous materials are fabricated based on surface metallization. Metallized sponges with Ag and Cu are highly hydrophobic and are still hydrophobic under oil. The metallized sponges selectively adsorb oils from oil/water mixtures and can completely remove oils from water. We further demonstrate continuous oil-water separation by the metallized sponges with the aid of a peristaltic pump. The Ag-metallized materials show high catalytic performance for both chemical reduction and dye degradation. The catalytic reduction efficiency of 4-nitrophenol reaches 97.7% within 60 min and remains as high as 96% after 15 cycles. Moreover, the metallized materials show 99.99% bactericidal efficiency for both Staphylococcus aureus and Escherichia coli. Particularly, the Cu-metallized materials exhibit stable conductivity under deformation; and metal patterns are realized via the metallization method combined with a patterned mask, which may provide a feasible approach for flexible electronics. This work provides a versatile method to introduce metal coatings to porous materials, broadening the applications of porous materials.

Surface Deposition of Juglone/FeIII on Microporous Membranes for Oil/Water Separation and Dye Adsorption.

Deposition of dopamine and tannic acid has received great attention in the fields of surface and interface science and technology. The deposition behaviors of various metal-phenolic systems have been investigated, and it is generally accepted that at least one catechol group is essential to the formation of the coatings. Herein, we report a novel and effective surface-coating system based on the coordination complexes of FeIII ions with a natural product juglone that contains only one phenolic hydroxyl. We investigated the deposition behaviors of this novel system on various substrates. Microporous polypropylene membrane modified with juglone/FeIII coatings is superhydrophilic and underwater superoleophobic, showing high separation efficiency and good reusability for various oil/water emulsions. In addition, the modified membrane can adsorb anionic dyes and selectively remove them from dye mixtures with high efficiency. We further demonstrated that the coating is a result of the synergetic effect of juglone/FeIII coordination and FeIII hydrolysis. This work not only provides new insights into surface deposition systems but also expands the polyphenol family for surface coatings of multifunctional materials.

CuSO4/H2O2-Induced Rapid Deposition of Polydopamine Coatings with High Uniformity and Enhanced Stability.

Mussel-inspired polydopamine (PDA) deposition offers a promising route to fabricate multifunctional coatings for various materials. However, PDA deposition is generally a time-consuming process, and PDA coatings are unstable in acidic and alkaline media, as well as in polar organic solvents. We report a strategy to realize the rapid deposition of PDA by using CuSO4/H2O2 as a trigger. Compared to the conventional processes, our strategy shows the fastest deposition rate reported to date, and the PDA coatings exhibit high uniformity and enhanced stability. Furthermore, the PDA-coated porous membranes have excellent hydrophilicity, anti-oxidant properties, and antibacterial performance. This work demonstrates a useful method for the environmentally friendly, cost-effective, and time-saving fabrication of PDA coatings.

Highly Stable, Protein-Resistant Surfaces via the Layer-by-Layer Assembly of Poly(sulfobetaine methacrylate) and Tannic Acid.

Zwitterionic materials have received great attention because of the non-fouling property. As a result of the electric neutrality of zwitterionic polymers, their layer-by-layer (LBL) assembly is generally conducted under specific conditions, such as very low pH values or ionic strength. The formed multilayers are unstable at high pH or in a high ionic strength environment. Therefore, the formation of highly stable multilayers of zwitterionic polymers via the LBL assembly process is still challenging. Here, we report the LBL assembly of poly(sulfobetaine methacrylate) (PSBMA) with a polyphenol, tannic acid (TA), for protein-resistant surfaces. The assembly process was monitored by a quartz crystal microbalance (QCM) and variable-angle spectroscopic ellipsometry (VASE), which confirms the formation of thin multilayer films. We found that the (TA/PSBMA)n multilayers are stable over a wide pH range of 4-10 and in saline, such as 1 M NaCl or urea solution. The surface morphology and chemical composition were characterized by specular reflectance Fourier transform infrared spectroscopy (FTIR/SR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Furthermore, (TA/PSBMA)n multilayers show high hydrophilicity, with a water contact angle lower than 15°. A QCM was used to record the dynamic protein adsorption process. Adsorption amounts of bovine serum albumin (BSA), lysozyme (Lys), and hemoglobin (Hgb) on (TA/PSBMA)20 multilayers decreased to 0.42, 52.9, and 37.9 ng/cm(2) from 328, 357, and 509 ng/cm(2) on a bare gold chip surface, respectively. In addition, the protein-resistance property depends upon the outmost layer. This work provides new insights into the LBL assembly of zwitterionic polymers.

Polydopamine-Coated Porous Substrates as a Platform for Mineralized ß-FeOOH Nanorods with Photocatalysis under Sunlight.

Immobilization of photo-Fenton catalysts on porous materials is crucial to the efficiency and stability for water purification. Here we report polydopamine (PDA)-coated porous substrates as a platform for in situ mineralizing ß-FeOOH nanorods with enhanced photocatalytic performance under sunlight. The PDA coating plays multiple roles as an adhesive interface, a medium inducing mineral generation, and an electron transfer layer. The mineralized ß-FeOOH nanorods perfectly wrap various porous substrates and are stable on the substrates that have a PDA coating. The immobilized ß-FeOOH nanorods have been shown to be efficient for degrading dyes in water via a photo-Fenton reaction. The degradation efficiency reaches approximately 100% in 60 min when the reaction was carried out with H2O2 under visible light, and it remains higher than 90% after five cycles. We demonstrate that the PDA coating promotes electron transfer to reduce the electron-hole recombination rate. As a result, the ß-FeOOH nanorods wrapped on the PDA-coated substrates show enhanced photocatalytic performance under direct sunlight in the presence of H2O2. Moreover, this versatile platform using porous materials as the substrate is useful in fabricating ß-FeOOH nanorods-based membrane reactor for wastewater treatment.

Fabrication of perforated isoporous membranes via a transfer-free strategy: enabling high-resolution separation of cells.

Thin perforated membranes with ordered pores are ideal barriers for high-resolution and high-efficiency selective transport and separation of biological species. However, for self-assembled thin membranes with a thickness less than several micrometers, an additional step of transferring the membranes onto porous supports is generally required. In this article, we present a facile transfer-free strategy for fabrication of robust perforated composite membranes via the breath figure process, and for the first time, demonstrate the application of the membranes in high-resolution cell separation of yeasts and lactobacilli without external pressure, achieving almost 100% rejection of yeasts and more than 70% recovery of lactobacilli with excellent viability. The avoidance of the transfer step simplifies the fabrication procedure of composite membranes and greatly improves the membrane homogeneity. Moreover, the introduction of an elastic triblock copolymer increases the interfacial strength between the membrane and the support, and allows the preservation of composite membranes in a dry state. Such perforated ordered membranes can also be applied in other size-based separation systems, enabling new opportunities in bioseparation and biosensors.

Multiple interfaces in self-assembled breath figures.

This feature article describes the multiple interfaces in the breath figure (BF) method toward functional honeycomb films with ordered pores. If a drop of polymer solution in a volatile solvent such as carbon disulphide is placed in a humid environment, evaporative cooling leads to self-assembled arrays of condensed water droplets. After evaporation of the solvent and water, patterned pores can be formed. During this BF process, the interfaces between the solution and the substrate, the solution and water droplets, and the film surface and air play extremely important roles in determining both the structures and functions of the honeycomb films. Progress in the BF method is reviewed by emphasizing the roles of the interfacial interactions. The applications of hierarchical and functional honeycomb films in separation, biocatalysis, biosensing, templating, stimuli-responsive surfaces and adhesive surfaces are also discussed.

Polystyrenes with hydrophilic end groups: synthesis, characterization, and effects on the self-assembly of breath figure arrays.

We report the synthesis and characterization of a series of hydroxyl-end-functionalized polystyrenes (PS-OH) and the formation of patterned porous films. The polymers were synthesized by chain end reaction of polystyrene having a bromide end group (PS-Br) with hydramines including ethanolamine, diethanol amine, 2-amino-1,3-propanediol, and 2-(2-aminoethoxy) ethanol. The polymers were characterized by gel permeation chromatography (GPC), nuclear magnetic resonance (NMR), matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS), and differential scanning calorimetry (DSC). It was found that the end groups can influence the glass transition temperature (T(g)) of the polystyrenes. The polymers with different end groups were then used to prepare honeycomb-patterned porous films by the breath figure method. Results reveal that the subtle chain-end modification leads to a dramatic change in the morphology of the films. Honeycomb films with large area ordered structure can be easily prepared from PS-OH. Effects of the end groups as well as blending PS-OH with PS-Br on the surface pore diameter, pore center distance, and the hierarchical structure were studied in detail. As supported by the results of polymer hydrophilicity, in situ observation of the film formation process, as well as the chain mobility, the film structure is supposed to be mainly determined by the precipitation of polystyrene at the solution/water droplet interface and the interfacial activity enhanced by the end groups.

Polydopamine gradients by oxygen diffusion controlled autoxidation.

We report a simple and facile protocol to fabricate mussel-inspired polydopamine (PDA) gradients on different surfaces. An oxygen diffusion phenomenon was used for dopamine autoxidation to form thickness gradients of PDA on different substrates. These PDA gradients showed gradual changes in thickness, roughness, wettability and light transmittance.

Glycopolymer brushes for the affinity adsorption of RCA120: effects of thickness, grafting density, and epitope density.

The interactions between glycopolymer brushes and lectin are very important for the development of affinity membrane chromatography in protein separation. Here, we report the combination of surface-initiated atom transfer radical polymerization (SI-ATRP) and surface plasmon resonance (SPR) to investigate the relationship between the structure of glycopolymer brushes and the affinity adsorption of lectin. The glycopolymer brushes were fabricated from self-assembly of 11-mercapto-1-undecanol (MUD)/1-undecanethiol (UDT) mixture, immobilization of ATRP initiators, and then SI-ATRP of 2-lactobionamidoethyl methacrylate (LAMA). Brush thickness and grafting density were adjusted by controlling polymerization time and thiol ratio in MUD/UDT mixture, respectively. Sugar epitope density was also controlled through copolymerization of 2-hydroxylethyl methacrylate (HEMA) with LAMA. Ricinus communis agglutinin (RCA(120)), one kind of lectin that can bind galactose specifically, was chosen to study the effects of brush architectures on lectin adsorption. SPR results indicate not only the thickness but also the grafting density and the epitope density of glycopolymer brushes can achieve the best performance of sugar cluster effect in affinity adsorption of lectin. In addition, the mass transport effect is crucial in the adsorption process. We propose that it is important to keep the balance between the sugar cluster effect and the mass transport effect in the preparation of high-performance affinity membrane chromatography.

Interactions between polyacrylonitrile and solvents: density functional theory study and two-dimensional infrared correlation analysis.

Polyacrylonitrile (PAN) is a semicrystalline polymer with high polarity and is usually processed from solutions. Selected solvents for processing influence both the structure and properties of PAN products. We describe the interactions between PAN and various solvents by theoretical calculation based on density functional theories (DFT), and by experimental methods of Fourier transform infrared (FTIR) spectra and two-dimensional infrared (2D-IR) correlation analysis. The selected solvents include dimethyl sulfone (DMSO2), dimethyl sulfoxide (DMSO), ethylene carbonate (EC), propylene carbonate (PC), N,N-dimethyl formamide (DMF), and N,N-dimethyl acetamide (DMAc). Calculation results show that the PAN model monomer (PAN') interacts with each solvent through dipole-dipole interaction and formed PAN'-solvent complexes. Each complex displays an antiparallel alignment of interacting pair between the C≡N group of PAN' and the polar group of solvent molecule (S═O or C═O group). The calculated binding energies (ΔE) reveal that PAN' preferentially interacts with solvent in the order of DMSO2 > DMSO > EC > PC > DMF > DMAc. Red shifts of vibration frequencies are observed for C≡N, S═O, and C═O stretching bands. The C≡N stretching band shifts from 2245 cm(-1) in PAN to 2240, 2242, and 2241 cm(-1) in PAN-DMSO, PAN-EC, and PAN-DMF mixtures, respectively, indicating the existence of PAN-solvent interactions. Moreover, 2D-IR correlation analysis shows that as the PAN content increases, DMSO molecules vary prior to PAN-DMSO complexes, and change earlier than PAN bulk. However, PAN-EC and PAN-DMF mixtures follow the order of PAN bulk > PAN-solvent complexes > solvent molecules. This combination of theoretical simulation and experimental characterization is useful in selection of solvents for PAN or even other polar polymers and can provide an insight into the physical behavior of PAN-solvent complexes.

Patterned biocatalytic films via one-step self-assembly.

Patterned porous films containing enzymes have been facilely prepared via a one-step breath figure process, which is based on the self-assembly of horseradish peroxidase nanoparticles that show good resistance to organic solvents. The patterned biohybrid films possess robust catalytic activity.

Pore shape of honeycomb-patterned films: modulation and interfacial behavior.

The control of the pore size of honeycomb-patterned films has been more or less involved in most work on the topic of breath figures. Modulation of the pore shape was largely ignored, although it is important to applications in replica molding, filtration, particle assembly, and cell culture. This article reports a tunable pore shape for patterned films prepared from commercially available polystyrene (PS). We investigated the effects of solvents including tetrahydrofuran (THF) and chloroform (CF) and hydrophilic additives including poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA), poly(ethylene glycol) (PEG), and poly(N-vinyl pyrrolidone) (PVP). Water droplets on/in the polymer solutions were observed and analyzed for simulating the formation and stabilization of breath figures. Interfacial tensions of the studied systems were measured and considered as a main factor to modulate the pore shape. Results indicate that the pores gradually change from near-spherical to ellipsoidal with the increase of additive content when using CF as the solvent; however, only ellipsoidal pores are formed from the THF solution. It is demonstrated that the aggregation of the additives at the water/polymer solution interface is more efficient in the THF solution than that in the CF solution. This aggregation decreases the interfacial tension, stabilizes the condensed water droplets, and shapes the pores of the films. The results may facilitate our understanding of the dynamic breath figure process and provide a new pathway to prepare patterned films with different pore structures.