Selective Swelling Research Articles

Block copolymer coated carbon nanotube membrane anodes for enhanced and multipurpose hybrid capacitive deionization

Carbon nanotube (CNT) membranes are widely used electrode materials in capacitive deionization (CDI) processes, while the limited electrosorption capacity and poor long-term stability need to improve. In this work, a pH-responsive block copolymer (BCP), poly (2-dimethylaminoethyl methacrylate)-block-polystyrene (PDMAEMA-b-PS) is combined with the selective swelling to fabricate a CNT membrane based multipurpose electrode. After BCP coating and selective swelling, the PDMAEMA blocks migrate onto the membrane surface and protonate during the CDI processes, which enhance the attraction between electrode and anions. Therefore, the BCP coated electrodes can be used as high performance anodes in the hybrid CDI (HCDI) module. Experiment results show that the initial solution pH values have significant influence on the CDI performance of the HCDI module. The maximum removal efficiencies of the HCDI module towards NaCl and NaH2PO4 are ~15 mg·g−1 and ~38.7 mg·g−1, respectively. Moreover, the chemical and mechanical stabilities of the anodes are significantly enhanced. No anode oxidation can be observed during CDI processes and the frequently occurred co-ion repulsion effect is suppressed. Considering these advantages, the combination of BCPs and selective swelling will be a promising candidate for the development of HCDI module.

Selective Swelling and Functionalization of Integral Asymmetric Isoporous Block Copolymer Membranes.

SNIPS stands for a membrane fabrication technique that combines the evaporation induced self-assembly of the block copolymers and the classical nonsolvent induced phase separation. It is a one-step readily scalable technique to fabricate integral asymmetric isoporous membranes. The prominent developments in the last decade have carved out a niche for SNIPS as a potential technique to fabricate next generation isoporous membranes. In the last decade, a rich polymer library and variety of membrane postmodification routes have been successfully implemented to fabricate SNIPS membranes having the desired pore functionality. Some of these membranes form soft nanochannels in hydrated state due to swelling of the pore wall, i.e., the pore forming block of the block copolymer. These membranes having soft nanochannels have demonstrated the potential to perform several challenging separation tasks in ultrafiltration and nanofiltration. This paper highlights the currently accessible pore functionality, the strategies to tune the swelling of the soft nanochannels, the potential applications, and future perspectives of these membranes.

Multituning of Structural Color by Protonation and Conjugate Bases

The pH (acidity/alkalinity) and type of acid are crucial parameters affecting the thermodynamics, kinetics, and reaction mechanism of acid–base systems. However, most reported pH-responsive materials can only determine the pH and cannot identify the acid type. Herein, we report the selective swelling of polystyrene-b-poly(2-vinyl pyridine) (PS-b-P2VP) photonic crystals, which produces different morphologies with a change in pH or type of acid, based on Henderson–Hasselbalch principle and Coulomb coupling between pyridiniums and the conjugate bases. The swelling behavior in different acidic environments was modeled by the transfer matrix method (TMM), and the results were compared with the experimental reflectometry results. The thickness and refractive index of P2VP layers change with a change in H+ concentration or the hydration energy of the conjugate bases. Since the different morphologies produce distinct structural colors, the pH and type of acid can be directly identified visually. Furthermore, the structural color is affected by not only the molecular weight of PS-b-P2VP but also the cross-linking of the P2VP layers, which can shift the structural color wavelength, thereby changing the sensitivity to pH. Our findings can become a driving force to transcend the frontiers of conventional optical diagnostics or sensing technology.

Hollow-fiber membranes of block copolymers by melt spinning and selective swelling

Selective swelling of block copolymers has emerged as an efficient strategy to prepare ultrafiltration membranes with well-defined porosities. However, the application of this strategy is only limited to the preparation of flat-sheet membranes so far. Herein, we extend this selective swelling strategy, for the first time, to the preparation of hollow-fiber membranes (HFMs). A mechanically strong copolymer available at large scale, polysulfone-block-poly(ethylene glycol) (PSF-b-PEG), is employed as the membrane-forming polymer. The PSF-b-PEG melt without any diluters or additives exhibits good fluidity, enabling stable and continuous melt spinning of primary hollow fibers with dense fiber walls. Subsequent selective swelling in the mixture of n-propyl alcohol and acetone produces interconnected nanoporosities throughout the fiber walls, thus forming HFMs with PEG chains enriched on the membrane surface. The wall thicknesses as well as pore sizes, and thus the separation performances of the HFMs are tunable by changing the spinning and swelling parameters. In contrast to the strong hydrophobicity of HFMs prepared by cold stretching of polyolfins, our HFMs possess water-wettable surfaces due to the presence of PEG chains, and can be directly used in aqueous milieu. Because of the PSF-based skeleton and homogenous distribution of nanopores, the HFMs exhibit excellent tensile strengths up to 12.5 MPa, much higher than that of HFMs prepared by the commonly used phase inversion processes. Furthermore, the BSA rejection and water permeance of the HFMs currently can be tuned in the range of 29.9–88.2% and 13.7–119.3 L m-2·h-1·bar-1, respectively, by changing the spinning and/or swelling parameters. Their performances are expected to enhance by optimizing the hollow fiber geometries and pore structures. This strategy neither uses any solvents to fluidize the polymer nor produces wastewater, and therefore is a “cleaner” process. This work not only extends the usages of selective swelling, but also establishes a new process to manufacture HFMs.

Preparation of polysulfone-based block copolymer ultrafiltration membranes by selective swelling and sacrificing nanofillers

Preparation of polysulfone-based block copolymer ultrafiltration membranes by selective swelling and sacrificing nanofillers

Wireless Dual Stimuli Actuation of Dye Sensitized Conducting Polymer Hybrids

AbstractActuators controlled by external stimuli have received a lot of attention in recent years. Herein a polymer based dual stimuli actuator is reported, triggered by light and an electric field. This allows better control of actuation, enlarging the field of potential applications, like, for example, in the frame of soft robotics. The actuator is composed of polypyrrole and TiO2 modified with methylene blue. In an aqueous solution, the resulting freestanding hybrid film shows reversible actuation due to the synergy of light and an applied electric field. Illumination with light produces electron‐hole pairs in the TiO2 layer, which are shuttled to the opposite ends of the actuator by the potential gradient present in the solution. This results in electrochemical oxidation and reduction reactions at the two extremities and consequently in site selective swelling of the polymer, which finally leads to a controlled motion of the actuator, following the principles of logic gate operations. Such synergistically induced switching allows developing original actuation schemes for performing complex mechanical tasks triggered by more than one stimulus.

Design of Block-Copolymer Nanoporous Membranes for Robust and Safer Lithium-Ion Battery Separators.

Lithium‐ion batteries (LIBs) suffer from unsatisfied performance and safety risks mainly because of the separators. Herein, a block copolymer (BCP) composed of robust and electrolyte‐affinitive polysulfone (PSF) and Li+‐affinitive polyethylene glycol (PEG) is rationally designed to prepare a new type of LIB separator. The copolymer is subjected to selective swelling, producing nanoporous membranes with PEG chains enriched along the pore walls. Intriguingly, when used as LIB separators, thus‐produced BCP membranes efficiently integrate the merits of both PSF and PEG chains, endowing the separators thermal resistance as high as 150 °C and excellent wettability. Importantly, the nanoporous separator is able to close the pores with a temperature of 125 °C, offering the battery a thermal shutdown function. The membrane exhibits ultrahigh electrolyte uptake up to 501% and a prominent ionic conductivity of 10.1 mS cm−1 at room temperature. Batteries assembled with these membranes show excellent discharge capacity and C‐rate performance, outperforming batteries assembled from other separators including the extensively used Celgard 2400. This study demonstrates a facile strategy, selective swelling of block copolymer, to engineer high‐performance and safer LIB separators, which is also applicable to produce advanced copolymer‐based separators for other types of batteries.

Rapid Fabrication of Alcohol Responsive Photonic Prints with Changeable Color Contrasts for Anti‐Counterfeiting Application

AbstractEfficient fabrication of responsive photonic prints (RPPs) with specific functionalities is imminently desired owing to its applications in display, anti‐photobleaching, and anti‐counterfeiting. Here, RPPs with changeable color contrasts are fabricated through the region selective swelling of the swellable photonic crystals paper with 2‐hydroxyethyl methacrylate (HEMA) as ink followed by fixing the structures of the swelled regions by photopolymerization. The fabrication process is considerable simple, fast, and efficient, and multicolor RPPs with any desired patterns can be generated within 6 min. Different from the dual/triple color contrasts of conventional RPPs, the as‐prepared RPPs can instantly and reversibly show five color contrasts [(blue/transparent/green/yellow/red)‐red] in the alcohol solution owing to the asymmetric swelling behavior between the background and pattern. The similar solubility parameter between the photonic paper and HEMA/ethanol is the key for the fast fabrication process and abundant color contrasts of RPPs in solvents. The simple and rapid fabrications as well as the responsive properties will extend the applications of RPPs in color display, information storage, and anti‐counterfeiting.

Fast Evaporation Enabled Ultrathin Polymer Coatings on Nanoporous Substrates for Highly Permeable Membranes

SummaryThin polymer coatings covering on porous substrates are a common composite structure required in numerous applications, including membrane separation, and there is a strong need to push the coating thicknesses down to the nanometer scale to maximize the performances. However, producing such ultrathin polymer coatings in a facile and efficient way remains a big challenge. Here, uniform ultrathin polymer covering films (UPCFs) are realized by a facile and general approach based on rapid solvent evaporation. By fast evaporating dilute polymer solutions spread on the surface of porous substrates, we obtain ultrathin coatings (down to ∼30 nm) exclusively on the top surface of porous substrates, forming UPCFs with a block copolymer of polystyrene-block-poly(2-vinyl pyridine) at room temperature or a homopolymer of poly(vinyl alcohol) (PVA) at elevated temperatures. Upon selective swelling of the block copolymer and crosslinking of PVA, we obtain highly permeable membranes delivering ∼2–10 times higher permeance in ultrafiltration and pervaporation than state-of-the-art membranes with comparable selectivities. We have invented a very convenient but highly efficient process for the direct preparation of defective-free ultrathin coatings on porous substrates, which is extremely desired in different fields in addition to membrane separation.

Nanoconfined Crosslinked Poly(ionic liquid)s with Unprecedented Selective Swelling Properties Obtained by Alkylation in Nanophase-Separated Poly(1-vinylimidazole)-l-poly(tetrahydrofuran) Conetworks.

Despite the great interest in nanoconfined materials nowadays, nanocompartmentalized poly(ionic liquid)s (PILs) have been rarely investigated so far. Herein, we report on the successful alkylation of poly(1-vinylimidazole) with methyl iodide in bicontinuous nanophasic poly(1-vinylimidazole)-l-poly(tetrahydrofuran) (PVIm-l-PTHF) amphiphilic conetworks (APCNs) to obtain nanoconfined methylated PVImMe-l-PTHF poly(ionic liquid) conetworks (PIL-CNs). A high extent of alkylation (~95%) was achieved via a simple alkylation process with MeI at room temperature. This does not destroy the bicontinuous nanophasic morphology as proved by SAXS and AFM, and PIL-CNs with 15–20 nm d-spacing and poly(3-methyl-1-vinylimidazolium iodide) PIL nanophases with average domain sizes of 8.2–8.4 nm are formed. Unexpectedly, while the swelling capacity of the PIL-CN dramatically increases in aprotic polar solvents, such as DMF, NMP, and DMSO, reaching higher than 1000% superabsorbent swelling degrees, the equilibrium swelling degrees decrease in even highly polar protic (hydrophilic) solvents, like water and methanol. An unprecedented Gaussian-type relationship was found between the ratios of the swelling degrees versus the polarity index, indicating increased swelling for the nanoconfined PVImMe-l-PTHF PIL-CNs in solvents with a polarity index between ~6 and 9.5. In addition to the nanoconfined structural features, the unique selective superabsorbent swelling behavior of the PIL-CNs can also be utilized in various application fields.

Rheology-morphology relationships of new polymer-modified bitumen based on thermoplastic polyurethanes (TPU)

The present study reports a new type of polymer-modified bitumen (PMB) which considers the use of a thermoplastic polyurethane (TPU) as an alternative to conventional thermoplastic elastomers such as poly(styrene-b-butadiene-b-styrene) block copolymers. As for other block copolymers, the structure of the TPU, made of two types of segments which can microphase-separate, leads to its selective swelling by the oily fractions of bitumen. The poor compatibility of hard segments (HS) with bitumen is responsible for this partial swelling of the TPU by the maltene fractions. By varying the TPU content in the bitumen-TPU blend a dramatic change in viscoelastic properties for a TPU content close to 11 wt% is shown, with the appearance at high temperatures of an elastic response due to the percolation of the TPU-rich phase. This percolation phenomenon is highlighted by multiscale morphology characterizations and well described by a conventional mechanical percolation model. Different TPU architectures, i.e. different hard to soft segments ratios, are studied. The best compromise is found for a blend containing TPU with 13 wt% of HS as it displays a favorable swelling of percolated TPU rich phase while maintaining its viscoelastic behavior.

Feature size control using surface reconstruction temperature in block copolymer lithography for InAs nanowire growth

Here we present a method to control the size of the openings in hexagonally organized BCP thin films of poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP) by using surface reconstruction. The surface reconstruction is based on selective swelling of the P4VP block in ethanol, and its extraction to the surface of the film, resulting in pores upon drying. We found that the BCP pore diameter increases with ethanol immersion temperature. In our case, the temperature range 18 to 60 °C allowed fine-tuning of the pore size between 14 and 22 nm. A conclusion is that even though the molecular weight of the respective polymer blocks is fixed, the PS-b-P4VP pore diameter can be tuned by controlling temperature during surface reconstruction. These results can be used for BCP-based nanofabrication in general, and for vertical nanowire growth in particular, where high pattern density and diameter control are of importance. Finally, we demonstrate successful growth of indium arsenide InAs vertical nanowires by selective-area metal-organic vapor phase epitaxy (MOVPE), using a silicon nitride mask patterned by the proposed PS-b-P4VP surface reconstruction lithography method.

Spray coating of polysulfone/poly(ethylene glycol) block polymer on macroporous substrates followed by selective swelling for composite ultrafiltration membranes

Abstract Polysulfone (PSF) is extensively used for the production of ultrafiltration (UF) membranes thanks to its high strength, chemical stability, and good processibility. However, PSF is intrinsically hydrophobic, and hydrophilic modification is always required to PSF-based membranes if they are intended to be used in aqueous systems. Facile strategies to prepare hydrophilic PSF membranes are thus highly demanded. Herein we spray coat a PSF-based amphiphilic block polymer onto macroporous substrates followed by selective swelling to prepare flat-sheet PSF UF membranes. The polymer is a triblock polymer containing PSF as the majority middle block tethered with shorter block of polyethylene glycol (PEG) on both ends, that is, PEG-b-PSF-b-PEG. We use the technique of spray coating to homogeneously dispense diluted triblock polymer solutions on the top of macroporous supports, instantly resulting in uniform, defect-free polymer coating layers with the thickness down to ~ 1.2 μm. The bi-layered composite structures are then immerged in ethanol/acetone mixture to generate mesoscale pores in the coating layers following the mechanism of selective swelling-induced pore generation, thus producing composite membranes with the mesoporous triblock polymer coating as the selective layers. This facile strategy is free from additional hydrophilic modification and much smaller dosages of polymers are used compared to conventional casting methods. The pore sizes, porosities, hydrophilicity, and consequently the separation properties of the membranes can be flexibly tuned by changing the swelling duration and the composition of the swelling bath. This strategy combining spray coating and selective swelling is upscalable for the production of high-performance PSF UF membranes.

Room-temperature swelling of block copolymers for nanoporous membranes with well-defined porosities

Selective swelling of block copolymers (BCPs) has been an efficient way to produce nanoporous materials with well-defined porosities. Currently, the cavitation of bulk BCP films by selective swelling needs to be performed at elevated temperatures (typically 50–70 °C), which is not only tedious in operation but also energy extensive. Herein, we develop the room-temperature (RT) swelling strategy to enable pore formation in BCP films with no need of heating. Simply introducing a solvent selective to the majority blocks of BCPs into the swelling bath allows the initiation of selective swelling-induced pore generation at room temperature because of plasticizing effect on BCP matrix. The swelling degrees and porosities of BCP films can be flexibly tuned by changing the compositions of the swelling bath and the swelling durations. The universality of this RT swelling strategy is also demonstrated by its applicability to both polystyrene (PS)-based BCPs and polysulfone-based BCPs with high glass transition temperatures. We prepare composite membranes with nanoporous polystyrene-block-poly (2-vinyl pyridine) (PS-b-P2VP) selective layers on top of macroporous substrates by using this RT swelling approach. Interestingly, thus-produced membranes exhibit more uniform pores with narrow pore size distributions, resulting in better selectivity. RT swelling is featured as convenient and energy-saving, and is desired in large-scale manufacturing of nanoporous BCP materials for various applications.

Soft Photonic Fibers for Colorimetric Solvent Vapor Sensing

AbstractStimuli‐responsive elastomers are promising material systems for the development of optical sensors with visual outputs that can be easily assessed by the human eye. These materials, when shaped into alternating layers, form distributed Bragg reflectors (DBRs) that feature a high spectrally selective reflectivity. The adsorption of vapor molecules into these photonic structures leads to partial swelling in the constituent materials that can induce pronounced color changes. Here, it is demonstrated that soft photonic fibers with a DBR‐cladding can selectively sense and quantify different organic vapors. It is found that fibers with a multilayer cladding assembled of films of polydimethylsiloxane (PDMS) and a polystyrene‐polyisoprene block‐copolymer (PSPI) change color sensitively depending on the concentration of toluene, benzene, tetrahydrofuran, or chloroform vapors. It is shown that this is a direct consequence of a selective swelling of the constituent polymer layers due to vapor adsorption. With wavelength variations as small as 5 nm being noticeable to the human eye, such photonic fibers are interesting materials for optical sensors. Modifications of their building blocks and their structural morphology make these vapor‐sensing fibers a versatile platform for standalone and textile‐integrated solvent sensing systems applied in industrial and lab‐scale manufacturing processes.

Producing Nanoporosities in Block Copolymers within 30 s by Microwave-Boosted Selective Swelling

Nanoporous materials derived from block copolymers (BCPs), with rich morphological diversity and designable functionality, have attracted extensive interest in membrane separation, drug delivery, a...

Fabrication of a novel hollow fiber composite membrane with a double-layer structure for enhanced water treatment

In surface modification of polymer membranes, permeate flux is normally decreased with the enhancement of rejection and antifouling properties. Herein, a new method is proposed to beat the permeability–selectivity trade-off and endow polymer membranes with more functions: a double-layer polypropylene/styrene–maleic anhydride (SMA) copolymer hollow fiber composite membrane was fabricated via interfacial suspension copolymerization. The pore structure of the hydrophilic SMA layer was optimized by manipulating the polymerization and phase separation in the mixed solvents. The formation mechanism of the pores was systematically investigated. Phase separation, the length of the SMA molecular chain, and its selective swelling in the mixed solvents were the key factors for pore formation. Compared with the pristine membrane, the water flux of the optimized membrane PPM2 was significantly increased from 105.5 to 570.0 L/m2h, and rejections were highly elevated from 81.4% to 97.2% for bovine serum albumin (BSA), 49.8% to 96.5% for Congo red, and 17.6% to 68.9% for methylthionine chloride. The antifouling properties were simultaneously strengthened, and the flux recovery ratio was increased from 68.6% to 95.2% for the BSA solution and 71.5% to 92.8% for the oil/water (O/W) emulsion. The separation efficiency of the O/W emulsion was up to 99.9% because of the double-layer structure with asymmetric wettability.

선택적 팽윤을 이용한 블록공중합체 나노패턴의 집적도 향상

선택적 팽윤을 이용한 블록공중합체 나노패턴의 집적도 향상

Simultaneous zwitterionization and selective swelling-induced pore generation of block copolymers for antifouling ultrafiltration membranes

Membranes with zwitterionic surfaces are highly desired in water-based separations for their distinguished fouling resistance. Herein, a facile strategy for the preparation of zwitterion-functionalized membranes is developed by coupling the pore-making and zwitterion functionalization in one step. We soaked thin films of poly (2-dimethylaminoethyl methacrylate)-block-polystyrene (PDMAEMA-b-PS) in the mixture of ethanol and 1, 3-propanesultone (1, 3-PPST). In this mixture, PDMAEMA microdomains were selective swollen leading to nanoporous structures with PDMAEMA chains enriched on the surface. Simultaneously, the quaternization reaction between PDMAEMA and 1, 3-PPST took place. Unexpectedly, in addition to function as the zwitterionic agent, 1, 3-PPST also contributed to the selective swelling induced pore generation. It was found that the presence of 1, 3-PPST in ethanol slowed down the swelling process at the early stage, but evidently enhanced the swelling of PDMAEMA-b-PS films in longer duration. Thus-prepared zwitterion-functionalized membranes exhibited several times higher water permeance than non-zwitterionized counterparts, which should be attributed to increased pore size and strongly improved hydrophilicity as a result of zwitterion functionalization. Moreover, the membranes showed exceptional fouling resistance because of the presence of zwitterions.

Selective Swelling of Block Copolymers: An Upscalable Greener Process to Ultrafiltration Membranes?

Block copolymers (BCPs) have long been pursued as precursors to nanoporous membranes, and selective swelling-induced pore generation has emerged as an extremely simple strategy to BCP membranes wit...