Sulfonated Pentablock Copolymer Research Articles

Sulfonated Pentablock Copolymer (NexarTM) for Water Remediation and Other Applications.

This review focuses on the use of a sulfonated pentablock copolymer commercialized as NexarTM in water purification applications. The properties and the use of sulfonated copolymers, in general, and of NexarTM, in particular, are described within a brief reference focusing on the problem of different water contaminants, purification technologies, and the use of nanomaterials and nanocomposites for water treatment. In addition to desalination and pervaporation processes, adsorption and photocatalytic processes are also considered here. The reported results confirm the possibility of using NexarTM as a matrix for embedded nanoparticles, exploiting their performance in adsorption and photocatalytic processes and preventing their dispersion in the environment. Furthermore, the reported antimicrobial and antibiofouling properties of NexarTM make it a promising material for achieving active coatings that are able to enhance commercial filter lifetime and performance. The coated filters show selective and efficient removal of cationic contaminants in filtration processes, which is not observed with a bare commercial filter. The UV surface treatment and/or the addition of nanostructures such as graphene oxide (GO) flakes confer NexarTM with coating additional functionalities and activity. Finally, other application fields of this polymer are reported, i.e., energy and/or gas separation, suggesting its possible use as an efficient and economical alternative to the more well-known Nafion polymer.

Tailoring surface and bulk morphologies to control transport properties of sulfonated block copolymer films

We examine the effects of solvent composition and solution-casting protocol on the structure of a lamellar sulfonated pentablock copolymer (SPC) membrane. Films are prepared by a layering process, wherein the film is built up through sequential bar-coating steps. Process variables include bar gap height, which controls drying time and layer thickness, and solvent selectivity toward each block in the SPC, which controls solution-state structure and biases the domain orientations at the surface. We find that irrespective of solvent selectivity, one-layer films have poorly ordered structures in the bulk with minimal restructuring near the surface. However, when the process involves sequential deposition of two or more layers, then the bulk structure of dry films can be well-predicted by the solution-state structure, and domain orientations at the surface are templated by polymer-solvent interactions. Consequently, processing conditions strongly influence through-plane transport properties of the SPC films. When the casting process generates disordered lamellae in bulk with a perpendicular lamellar orientation at the surface, both water and protons can move across the film. However, when the process generates highly ordered lamellae in bulk and parallel lamellar orientations at the surface, transport of both water and protons is inhibited by limited pathways. Significantly, the methodology outlined in this work can be extended to other ionic block copolymer platforms, allowing researchers to tailor bulk and surface morphologies for optimization of critical transport properties.

Sulfonated Pentablock Copolymer with Graphene Oxide for Co2+ Ions Removal: Efficiency, Interaction Mechanisms and Secondary Reaction Products

In this work, sulfonated pentablock copolymer (s-PBC) and s-PBC mixed with graphene oxide (s-PBC_GO) layers were deposited on polypropylene (PP) fibrous filters and tested as active coatings for the removal of cobalt ions from water using adsorption and filtration processes. Some of the coated filters were treated by UV light irradiation to modify their hydrophilic properties. The filters were characterized, before and after the processes, by energy-dispersive X-ray (EDX) analysis and Fourier transform infrared spectroscopy (FT-IR). The Qt (mg/g) values, defined as the weight ratio between the removed ions and the coating layer, were evaluated. In the case of adsorption processes, the best results for the removal of Co2+ ions were achieved by the s-PBC_GO coating, with a Qt of 37 mg/g compared to 21 mg/g obtained by the s-PBC. This was ascribed to the presence of GO, which contains more favorable sites able to adsorb positive ions from the solution. Vice versa, for filtration processes, the s-PBC coated filters show similar or slightly better results than the s-PBC_GO coated ones. Such differences can be ascribed to the shorter contact time between the solution and the coating layer in the case of filtration, with respect to adsorption processes, thus reducing the chance for the ions to be adsorbed on the GO layers before passing through the filter. A collateral effect, observed in this study and enhanced in the case of UV-treated coatings, is the release of radical oxysulfur species. The mechanisms involved in this effect are discussed and identified as a consequence of the interaction between the coating layers and metal ions. In order to identify the mechanism of oxysulfur radicals formation and considering a water sample closer to real water, the Co2+ ions adsorption experiments were conducted in the presence of a competitive organic contaminant (i.e., methyl orange, MO).

Sulfonated Pentablock Copolymer Membrane Morphological Anisotropy and Its Impact on Dimensional Swelling, Proton Conductivity, and the Transport of Protons and Water

Poly[t-butylstyrene-b-(ethylene-alt-propylene)-b-(styrene-co-styrene sulfonate)-b-(ethylene-alt-propylene)-b-t-butylstyrene], a pentablock copolymer (PBC), was solution-cast into membranes as a function of the ion-exchange capacity (IEC) using cyclohexane and heptane (PBC[C/H]) or tetrahydrofuran (PBC[THF]) to study its anisotropic morphology and transport. Orientation-dependent transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) were used to characterize its morphology in the xy-plane (surface) and the xz-plane (thickness). PBC[C/H] had a random morphology of dispersed spherical-like sulfonated domains regardless of the IEC. An orientation-dependent lamellar morphology was formed in PBC[THF]. At IEC = 2.0, PBC2.0[C/H] and PBC2.0[THF] had orientation-dependent proton conductivity through the xz-plane and xy-plane. The membrane proton conductivities of PBC2.0[C/H] were 114.4 (xz-plane) and 103.6 mS/cm (xy-plane), which became 124.4 (xz-plane) and 24.4 mS/cm (xy-plane) for PBC2.0[THF]. Membrane water vapor flux and diffusivity through the xy-plane were 1.26 × 10–3 mol/(m2 s) and 1.52 ×10–10 m2/s for PBC2.0[C/H], respectively. The lamellar morphology within PBC2.0[THF] reduced its water transport properties to 3.84 × 10–4 mol/(m2s) and 3.86 × 10–11 m2/s. A disordered morphology is less anisotropic than an ordered one.

Sulfonated Pentablock Copolymer Coating of Polypropylene Filters for Dye and Metal Ions Effective Removal by Integrated Adsorption and Filtration Process.

In this work, we coated polypropylene (PP) fibrous filters with sulfonated pentablock copolymer (s-PBC) layers and tested them for the removal of cationic organic dyes, such as methylene blue (MB), and heavy metal ions (Fe3+ and Co2+) from water by adsorption and filtration experiments. Some of the coated filters were irradiated by UV light before being exposed to contaminated water and then were tested with unirradiated filters in the same adsorption and filtration experiments. Polymer-coated filters showed high efficiency in removing MB from an aqueous solution in both absorption and filtration processes, with 90% and 80% removal, respectively. On the other hand, for heavy metal ions (Fe3+ and Co2+), the coated filters showed a better removal performance in the filtration process than for the adsorption one. In fact, in the adsorption process, controlled interaction times allow the ionic species to interact with the surface of the filters leading to the formation and release of new species in solution. During filtration, the ionic species are easily trapped in the filters, in particular by UV modified filters, and we observed for Fe3+ ions a total removal (>99%) in a single filtration process and for Co2+ ions a larger removal with respect to the untreated filter. The mechanisms involved in the removal of the contaminants processes were investigated by characterizing the filters before and after use by means of scanning electron microscopy (SEM) combined with energy-dispersive X-ray (EDX) analysis and Fourier transform infrared spectroscopy (FT-IR).

Innovative Antibiofilm Smart Surface against Legionella for Water Systems

Legionella pneumophila contamination of water systems is a crucial issue for public health. The pathogen is able to persist in water as free-living planktonic bacteria or to grow within biofilms that adhere to and clog filters and pipes in a water system, reducing its lifespan and, in the case of hospital buildings, increasing the risk of nosocomial infections. The implementation of water management is considered to be the main prevention measure and can be achieved from the optimization of water system architecture, notably introducing new materials and strategies to contrast Legionella biofilm proliferation and so prolong the water system functionality. In this research, we propose a new smart surface against L. pneumophila biofilm formation. This is based on an innovative type of coating consisting of a sulfonated pentablock copolymer (s-PBC, commercially named Nexar™) deposited on top of a polypropylene (PP) coupon in a sandwich filter model. The covering of PP with s-PBC results in a more hydrophilic, acid, and negatively charged surface that induces microbial physiological inhibition thereby preventing adhesion and/or proliferation attempts of L. pneumophila prior to the biofilm formation. The antibiofilm property has been investigated by a Zone of Inhibition test and an in vitro biofilm formation analysis. Filtration tests have been performed as representative of possible applications for s-PBC coating. Results are reported and discussed.

Antimicrobial s-PBC Coatings for Innovative Multifunctional Water Filters.

Biological contamination is a typical issue in water treatment. Highly concentrated microbial suspensions in a water flow may cause filter occlusion and biofilm formation, affecting the lifespan and quality of water purification systems and increasing the risk of nosocomial infections. In order to contrast the biofilm formation, most of the conventional strategies rely on the water chemical modification and/or on the use of filters functional coatings. The former is unsafe for huge chemicals spilling required; therefore, we focus on the second approach and we propose the use of a sulfonated pentablock copolymer (s-PBC, commercially named Nexar™) as innovative multifunctional coating for improving the performance of commercial water filters. S-PBC-coated polypropylene (PP) samples were tested against the pathogen Pseudomonas aeruginosa. The covering of PP with s-PBC results in a more hydrophilic, acid, and negatively charged surface. These properties avoid the adhesion and proliferation attempts of planktonic bacteria, i.e., the biofilm formation. Inhibition tests were performed on the as-modified filters and an evident antibacterial activity was observed. The results point out the possibility of using NexarTM as coating layer for filters with antifouling properties and a simultaneous ability to remove bacteria and cationic dyes from water.

Sulfonated Pentablock Copolymer Membranes and Graphene Oxide Addition for Efficient Removal of Metal Ions from Water.

Nowadays heavy metals are among the higher environmental priority pollutants, therefore, the identification of new, effective, reusable and easy-to-handle adsorbent materials able to remove metal ions from water is highly desired. To this aim, in this work for the first time, sulfonated pentablock copolymer (s-PBC, Nexar™) membranes and s-PBC/graphene oxide (GO) nanocomposite membranes were investigated for the removal of heavy metals from water. Membranes were prepared by drop casting and their chemical, structural and morphological properties were characterized using scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, dynamic mechanical analysis (DMA) and small-angle X-ray scattering (SAXS). The adsorption abilities and adsorption kinetics of both the polymer and the s-PBC/GO nanocomposite were investigated for the removal of different heavy metal ions (Ni2+, Co2+, Cr3+ and Pb2+) from aqueous solutions containing the corresponding metal salts at different concentrations. The investigated s-PBC membrane shows a good efficiency, due to the presence of sulfonic groups that play a fundamental role in the adsorption process of metal ions. Its performance is further enhanced by embedding a very low amount of GO in the polymer allowing an increase by at least three times of the adsorption efficiencies of the polymer itself. This can be ascribed to the higher porosity, higher roughness and higher lamellar distances introduced by GO in the s-PBC membrane, as evidenced by the SEM and SAXS analysis. Both the polymeric materials showed the best performance in removing Pb2+ ions.

Applicability of a New Sulfonated Pentablock Copolymer Membrane and Modified Gas Diffusion Layers for Low-Cost Water Splitting Processes

The aim of this work is to evaluate the possible use of Nexar™ polymer, a sulfonated pentablock copolymer (s-PBC), whose structure is formed by tert-butyl styrene, hydrogenated isoprene, sulfonated styrene, hydrogenated isoprene, and tert-butyl styrene (tBS-HI-SS-HI-tBS), as a more economical and efficient alternative to Nafion® membrane for proton exchange membrane (PEM) electrolysis cells. Furthermore, we have studied a new methodology for modification of gas diffusion layers (GDL) by depositing Pt and TiO2 nanoparticles at the cathode and anode side, respectively, and a protective polymeric layer on their surface, allowing the improvement of the contact with the membrane. Morphological, structural, and electrical characterization were performed on the Nexar™ membrane and on the modified GDLs. The use of modified GDLs positively affects the efficiency of the water electrolysis process. Furthermore, Nexar™ showed higher water uptake and conductivity with respect to Nafion®, resulting in an increased amount of current generated during water electrolysis. In conclusion, we show that Nexar™ is an efficient and cheaper alternative to Nafion® as the proton exchange membrane in water splitting applications and we suggest a possible methodology for improving GDLs’ properties. These results meet the urgent need for low-cost materials and processes for hydrogen production.

Self assembled, sulfonated pentablock copolymer cation exchange coatings for membrane capacitive deionization

A partially sulfonated pentablock copolymer is implemented as an ion-exchange coating for membrane capacitive deionization revealing trade-offs in water uptake, salt permeability, morphology, and performance.

Highly effective and reusable sulfonated pentablock copolymer nanocomposites for water purification applications

Sulfonated pentablock copolymer nanocomposites loaded with TiO2 or graphene oxide show their effectiveness in water purification applications.

Predicting the solution morphology of a sulfonated pentablock copolymer in binary solvent mixtures

ABSTRACTThe solution morphologies of a midblock‐sulfonated pentablock copolymer in miscible polar/nonpolar solvent blends were characterized as a function of solvent composition and polymer concentration using small angle X‐ray scattering. Three distinct solution morphologies are observed upon changing the composition of the solvent blend. At low weight fractions of polar solvent, spherical, sulfonated‐core micelles are observed, while spherical, sulfonated‐corona (inverted) micelles are observed at high weight fractions of polar solvent. Polymer solution scattering is observed at intermediate concentrations of polar solvent. Additionally, the characteristic dimensions of the sulfonated‐core micelles were found to change strongly upon variation of the solvent blend composition, indicating that these solutions—and correspondingly the morphology and properties of polymer membranes into which they are cast—can be tuned through simple variations in the solvent blend chemistry. We demonstrate that the solution morphologies and the characteristic micelle dimensions of these complex pentablock copolymer/binary solvent blends can be reliably predicted by considering the relative interactions of each polymer block and the solvent blend using the Hansen solubility parameters. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 254–262

Layer-by-layer (LbL) polyelectrolyte membrane with Nexar™ polymer as a polyanion for pervaporation dehydration of ethanol

Novel LbL polyelectrolyte multilayer membrane (PEMM) with Nexar™ polymer, a sulfonated pentablock copolymer, as the polyanion on a hydrolyzed polyacrylonitrile (PAN) hollow fiber substrate has been developed for pervaporation dehydration of ethanol. The advantages of applying the sulfonated copolymer as the polyanion are that the required bi-layer numbers can be significantly reduced while achieving a good separation performance. With just one bi-layer of polyethyleneimine (PEI) polycation and Nexar™ polyanion, the newly developed PEMM shows a flux of 1160g/m2h and a separation factor of 127 at 50°C for ethanol dehydration. The PEMM exhibits good stability up to a 170-h continuous operation with a flux decline at the initial stage because of substrate densification. This study demonstrates the possibility of employing the sulfonated pentablock copolymer as a polyanion for PEMMs to dehydrate biofuel via pervaporation.

Mechanical and microstructural characterization of sulfonated pentablock copolymer membranes

ABSTRACTCreep experiments utilizing a membrane inflation geometry were used to characterize the mechanical properties of pentablock copolymer membranes designed for water purification applications. Membranes were formed by casting from micellar solutions, and structure development during the casting process was followed in real time with grazing incidence small angle X‐ray scattering. The thin film morphologies were consistent with previously published results obtained for much thicker solvent cast films. The biaxial creep compliance of the films for applied stresses in the megapascal range increased substantially as the degree of sulfonation and consequent hydration of the middle block was increased. The sulfonation level was much more important than the overall degree of ordering in determining the creep compliance of the hydrated membranes. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 39–47

Novel nanofiltration membranes consisting of a sulfonated pentablock copolymer rejection layer for heavy metal removal.

Facing stringent regulations on wastewater discharge containing heavy metal ions, various industries are demanding more efficient and effective treatment methods. Among the methods available, nanofiltration (NF) is a feasible and promising option. However, the development of new membrane materials is constantly required for the advancement of this technology. This is a report of the first attempt to develop a composite NF membrane comprising a molecularly designed pentablock copolymer selective layer for the removal of heavy metal ions. The resultant NF membrane has a mean effective pore diameter of 0.50 nm, a molecular weight cutoff of 255 Da, and a reasonably high pure water permeability (A) of 2.4 LMH/bar. The newly developed NF membrane can effectively remove heavy metal cations such as Pb(2+), Cd(2+), Zn(2+), and Ni(2+) with a rejection of >98.0%. On the other hand, the membrane also shows reasonably high rejections toward anions such as HAsO4(2-) (99.9%) and HCrO4(-) (92.3%). This performance can be attributed to (1) the pentablock copolymer's unique ability to form a continuous water transport passageway with a defined pore size and (2) the incorporation of polyethylenimine as a gutter layer between the selective layer and the substrate. To the best of our knowledge, this is the first reported NF membrane comprising this pentablock copolymer as the selective material. The promising preliminary results achieved in this study provide a useful platform for the development of new NF membranes for heavy metal removal.

Highly Permeable Double-Skinned Forward Osmosis Membranes for Anti-Fouling in the Emulsified Oil–Water Separation Process

Forward osmosis (FO) has attracted wide attention in recent years. However, the FO performance may be restricted due to internal concentration polarization (ICP) and fast fouling propensity that occurs in the membrane sublayer. Particularly, these problems significantly affect the membrane performance when treating highly contaminated oily wastewater. Recently, double-skinned flat sheet cellulose acetate (CA) membranes consisting of two selective skins via the phase inversion method have demonstrated less ICP and fouling propensity over typical single-skinned membranes. However, these membranes exhibit low water fluxes of <12 LMH under 2 M NaCl draw solution. Therefore, a novel double-skinned FO membrane with a high water flux has been aimed for in this study for emulsified oil-water treatment. The double-skinned FO membrane comprises a fully porous sublayer sandwiched between (i) a truly dense skin for salt rejection and (ii) a fairly loose dense skin for emulsified oil particle rejection. The former dense skin is a polyamide synthesized via interfacial polymerization, while the latter one is a self-assembled sulfonated pentablock copolymer (Nexar copolymer) layer. The resultant double-skinned membrane exhibits a high water flux of 17.2 LMH and a low reverse salt transport of 4.85 gMH using 0.5 M NaCl as the draw solution and DI water as the feed. The double-skinned membrane outperforms the single-skinned membrane with much lower fouling propensity for emulsified oil-water separation.

Effects of neutralization with Et3Al on structure and properties in sulfonated styrenic pentablock copolymers

The effect of neutralization with Et3Al on morphologies in a sulfonated pentablock copolymer solution and cast membrane was investigated using small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The sulfonated pentablock copolymer in a non-polar solvent mixture (cyclohexane/heptane) persists as spherical micelles after neutralization where the micelle core of sulfonated polystyrene (SS) incorporates Al (3+) ions and the corona is solvated hydrogenated isoprene (HI) and t-butylstyrene (tBS). Membranes cast from this micellar solution exhibit a bicontinuous microphase separated morphology with interconnected SS microdomains. The aluminum-neutralized membrane with a continuous transport channel shows excellent water vapor transport rate (WVTR) (22kg/(m2day)), which is comparable to the WVTR of membranes in the sulfonic acid form. The strong interaction between Al(3+) ions and the sulfonic acid group in the aluminum-neutralized membrane results in significantly lower water uptake (∼30wt%) that provides much-improved mechanical stability in the wet state.

Characterization of a sulfonated pentablock copolymer for desalination applications

Water and salt transport properties were determined in a family of sulfonated pentablock copolymers to characterize their potential as chlorine-tolerant desalination membrane materials. The degree of sulfonation, block molecular weight, and casting conditions can be independently varied to tune the transport properties of these materials. Data for water uptake, water permeability, salt permeability, and apparent surface charge are presented. Apparent diffusion coefficients of water in these materials were calculated using the solution-diffusion theory. Generally speaking, water sorption, water diffusivity, water permeability, and salt permeability increase with increasing degree of sulfonation. As ion exchange capacity increases from 0.4 to 2.0 meq/g (dry polymer), water uptake values vary between 21% and 118%, and water permeability values, in units of cm2 s−1, vary over 4 orders of magnitude. Salt permeability depends on both the upstream sodium chloride concentration, between 0.01 and 1.0 mol L−1, and the degree of sulfonation. Both water permeability and salt permeability are sensitive to the conditions used when casting the polymer films. Apparent surface charge, as characterized by zeta potential, has been shown to be related to the fouling tendency of several membrane materials. In these materials, zeta potential is most negative in samples with low levels of sulfonation and is near neutral in samples with the highest level of sulfonation.

Micellar Morphology in Sulfonated Pentablock Copolymer Solutions

The morphology of solutions of poly[t-butyl styrene-b-hydrogenated isoprene-b-sulfonated styrene-b-hydrogenated isoprene-b-t-butyl styrene] (tBS-HI-SS-HI-tBS) pentablock copolymers with a range of sulfonation levels was studied by small-angle X-ray scattering and transmission electron microscopy. For dilute pentablock copolymer solutions, TEM confirms the spherical micellar morphology. Small-angle X-ray scattering results and their interpretation using the Kinning−Thomas model reveal that sulfonated pentablock copolymer solutions with all levels of sulfonation exhibit spherical micellar morphologies with a core of SS and a corona of solvated HI-tBS. Both the radius of the micelle core and the closest approach distance between cores increase with sulfonation level, while the number density of micelles decreases. The calculated fraction of micelles per unit volume shows an increase and then a plateau with sulfonation level. The manipulation of micelle size dramatically impacts the processability.