Hydrophilic Sulfonic Acid Groups Research Articles

Enhancement of CO2 separation efficiency in mixed matrix membranes through zinc ion modified g‐C3N4 nanosheets

AbstractThis study employed modified graphitic carbon nitride (g‐C3N4) nanosheets and polyether block amide (Pebax) to prepare mixed matrix membranes (MMMs) aiming to enhance CO2 separation efficiency. Through sulfonation and zinc ion (Zn2+) modification of g‐C3N4 nanosheets, high Zn2+ loaded nanofillers (SCN‐Zn2+) were synthesized. Compared to g‐C3N4, MMMs with SCN‐Zn2+ as nanofiller showed a CO2 permeance of 462 Barrer as well as the CO2/N2 selectivity of 47.5 at the feed gas pressure of 2 bar, which surpassed the 2008 Robeson upper bound. Additionally, the Pebax/SCN‐Zn2+(30) membrane was subjected to continuous gas permeability experiments for 70 h and showed good stability. The results showed that SCN‐Zn2+ nanosheets played an important role in enhancing the gas selectivity of the membranes. SEM confirmed that the SCN‐Zn2+ nanosheets had good compatibility with the Pebax substrate and the presence of hydrophilic sulfonic acid groups effectively suppressed the interfacial defects. The increase in the free volume fraction of the membranes as well as the solubility and diffusion coefficient suggested that the introduction of g‐C3N4 nanosheets led to more tortuous gas transport paths, which enhanced the permeability and selectivity of CO2.

Engineering tribological rehydration of cartilage interfaces: Assessment of potential polyelectrolyte mechanisms

Articular cartilage, primarily composed of water and collagen, is vital for synovial joint function. Traditional hard biomaterials like ceramic or cobalt-chrome used in hemiarthroplasty often result in abnormal contact pressures and premature implant failure. This study investigates the tribological properties of polyelectrolyte functionalised PEEK (SPMK-g-PEEK) in contact with cartilage, proposing a solution to these issues by utilising tribological rehydration and effective aqueous lubrication.We demonstrate a new mode of polyelectrolyte enhanced tribological rehydration where SPMK-g-PEEK achieves low friction and promotes interstitial fluid recovery during sliding, independent of traditional hydrodynamic theories. This results in a rapid stabilisation of the coefficient of friction (CoF) to levels comparable to natural cartilage (CoF ∼ 0.01) and aids in approximately 8% cartilage strain recovery, indicating effective tribological rehydration even under cartilage degradation or altered osmotic conditions.Furthermore, we find that lubrication and rehydration against an SPMK-g-PEEK interface depend minimally on biphasic lubrication but significantly on the hydrophilic sulfonic acid groups of SPMK, which act as a fluid reservoir. Our findings suggest SPMK-g-PEEK as a promising biomaterial for cartilage interfacing implants that offer low friction and modulate cartilage interstitial fluid pressure. This study enhances our understanding of biotribological interactions and contributes to the development of joint replacement materials that support the natural function of cartilage.

Nanoscale Stabilization Mechanism of Sodium Sulfate Decahydrate at Polyelectrolyte Interfaces.

Sodium sulfate decahydrate (SSD) is a low-cost phase-change material (PCM) for thermal energy storage applications that offers substantial melting enthalpy and a suitable temperature range for near-ambient applications. However, SSD's consistent phase separation with decreased melting enthalpy over repeated thermal cycles limits its application as a PCM. Sulfonated polyelectrolytes, such as dextran sulfate sodium (DSS), have shown great effectiveness in preventing phase separation in SSD. However, there is limited understanding of the stabilization mechanism of SSD by DSS at the atomic length and time scales. In this work, we investigate SSD stabilization via DSS using neutron scattering and molecular dynamics (MD) simulations. Neutron scattering and pair distribution function analysis revealed the structural evolution of the PCM samples below and above the phase change temperatures. MD simulations revealed that water from the hydrate structure migrates from the hydrate crystal to the SSD-DSS interfacial region upon melting. The water is stabilized at this interface by aggregation around the hydrophilic sulfonic acid groups attached to the backbone of the polyelectrolyte. This architecture retains water near the dehydrated sodium sulfate, preventing phase separation and, consequently, stabilizing SSD rehydration. This work provides atomistic insight into selecting and designing stable and high-performance PCMs for heating and cooling applications in building technologies.

Quantitative tailoring of water state of sulfonated corncob for boosting solar interfacial evaporation and salt resistance

Previous researches on carbon-based solar interfacial evaporation (SIE) have mainly focused on improving the solar absorption, neglecting the effect of water state on the SIE performance. This study proposes an easy strategy by combining carbonization and sulfonation using corncob as the carbon source and concentrated sulfuric acid (H2SO4) as the sulfonating agent to obtain sulfonated carbonized corncob (SCC) samples. The intermediate water to free water (IW/FW) ratio in the range of 0.53–0.96 within SCC samples has been tailored, which depends on the amount of hydrophilic sulfonic acid groups grafted on SCC. It is found that the amount of hydrophilic sulfonic acid groups and porous structure should be optimal in SCC for high IW/FW ratio. The optimized sample named as SCC-2-4.5 with a high IW/FW ratio of 0.96 and similar surface area to carbonized corncob exhibits the low enthalpy of water evaporation of 1800 J g−1, achieving the evaporation rate of 3.16 kg m−2 h−1 and evaporation efficiency of 159%. Meanwhile, SCC-2-4.5 realizes an effective separation of Na+ and Cl−, thanks to the electrostatic repulsion caused by its negatively charged sulfonic acid groups. This study provides an effective technique for regulating water state for carbon-based SIE devices on the molecular level.

Micelle formation of sodium taurolithocholate

The proportion of sodium taurolithocholate (NaTLC) is extremely low in human bile salts. NaTLC forms aggregates with other lipids in the bile and functions as an emulsifying and solubilizing agent. The molecular structure of NaTLC contains hydrophilic hydroxyl and sulfonic acid groups at both ends of the steroid ring. This molecular structure is similar to bolaform amphiphilic substance having hydrophilic groups at both ends due to the characteristics of its molecular structure. This study investigated the aggregate properties of the NaTLC using surface tension measurements, light scattering, small-angle X-ray scattering (SAXS), and cryo-transmission electron microscopy (cryo-TEM). Surface tension measurement showed that the surface tension of the NaTLC solution decreased to 54 mN m−1. The concentration that showed the minimum surface tension corresponded to the critical micelle concentration (CMC: 0.6 mmol L−1, 308 K) determined by the change in light scattering intensity. On the other hand, the degree of counterion (sodium ions) binding to the micelles increased with increasing NaTLC concentration. SAXS and cryo-TEM measurements showed that the NaTLC formed large string-like micelles. The surface activity and large aggregates showed the potential for use as biosurfactants. However, because of the relatively low solubility of NaTLC in water, its use as a biosurfactant is limited to a narrow concentration range.

Highly lubricious SPMK-g-PEEK implant surfaces to facilitate rehydration of articular cartilage

To enable long lasting osteochondral defect repairs which preserve the native function of synovial joint counter-face, it is essential to develop surfaces which are optimised to support healthy cartilage function by providing a hydrated, low friction and compliant sliding interface. PEEK surfaces were modified using a biocompatible 3-sulfopropyl methacrylate potassium salt (SPMK) through UV photo-polymerisation, resulting in a ∼350 nm thick hydrophilic coating rich in hydrophilic anionic sulfonic acid groups. Characterisation was done through Fourier Transformed Infrared Spectroscopy, Focused Ion Beam Scanning Electron Microscopy, and Water Contact Angle measurements.Using a Bruker UMT TriboLab, bovine cartilage sliding tests were conducted with real-time strain and shear force measurements, comparing untreated PEEK, SPMK functionalised PEEK (SPMK-g-PEEK), and Cobalt Chrome Molybdenum alloy. Tribological tests over 2.5 h at physiological loads (0.75 MPa) revealed that SPMK-g-PEEK maintains low friction (μ< 0.024) and minimises equilibrium strain, significantly reducing forces on the cartilage interface. Post-test analysis showed no notable damage to the cartilage interfacing against the SPMK functionalised surfaces.The application of a constitutive biphasic cartilage model to the experimental strain data reveals that SPMK surfaces increase the interfacial permeability of cartilage in sliding, facilitating fluid and strain recovery. Unlike previous demonstrations of sliding-induced tribological rehydration requiring specific hydrodynamic conditions, the SPMK-g-PEEK introduces a novel mode of tribological rehydration operating at low speeds and in a stationary contact area. SPMK-g-PEEK surfaces provide an enhanced cartilage counter-surface, which provides a highly hydrated and lubricious boundary layer along with supporting biphasic lubrication.Soft polymer surface functionalisation of orthopaedic implant surfaces are a promising approach for minimally invasive synovial joint repair with an enhanced bioinspired polyelectrolyte interface for sliding against cartilage. These hydrophilic surface coatings offer an enabling technology for the next generation of focal cartilage repair and hemiarthroplasty implant surfaces.

Synthesis of a Ternary Polysulfonate Dispersant and Its Suspension Performance

Allyl alcohol polyoxyethylene ether (APEG), hydroxyethyl methacrylate (HEMA) and styrene sodium sulfonate (SSS) were used as monomers to obtain a APEG-HEMA-SSS comb-like polymer, which was employed as the polysulfonate dispersant for pendimethalin suspensions in this paper. The comb-like polymer has an anionic polysulfonate backbone, hydrophilic APEG side chains and sulfonic acid groups, which makes the dispersant absorb easily on the surface of pendimethalin particles. The polysulfonate dispersant with good dispersion performance was screened out by orthogonal experiments. The surface tension, zeta potential, particle size and dynamic contact angle of the pendimethalin suspension with APEG-HEMA-SSS as dispersant were investigated. The dispersant improves the dispersibility and wettability of the pendimethalin suspension observably.

Densely functionalized proton exchange membrane from sulfonated poly(aryl ether ketone) containing multiple flexible side chains for fuel cell

Proton exchange membranes play a pivotal role in boosting the efficiency of fuel cells and hence focused research in this area is highly desirable. Here we report that a series of poly(aryl ether ketone)s with amino and trifluoromethyl units (AFPAEK) were synthesized by nucleophilic substitution polycondensation. Subsequently, sulfonated poly(aryl ether ketone) (SAFPAEK) membranes were prepared with amino groups of AFPAEKs as reaction sites to densely graft alkyl sulfonate side chains. This special structure of hydrophilic backbone containing trifluoromethyl groups and hydrophilic sulfonic acid groups generated nano-sized proton channels. The facilitated transportation of protons and cations through these membranes enables the prepared membranes to obtain high IEC and desirable proton conductivity. In particular, the SAFPAEK-50 membrane exhibits high proton conductivity from 0.077 to 0.179 S cm−1, which is higher than that of Nafion 115 over the entire temperature range. Meanwhile, SAFPAEK membranes possess excellent mechanical properties and favorable stability (thermal stability and oxidation stability). Importantly, SAFPAEK-50 displays a peak power density of 70.9 mW cm−2 at 158.8 mA cm−2 in a direct borohydride‑hydrogen peroxide fuel cell, which is higher than that of Nafion 115 (60.9 mW cm−2 at 151.2 mA cm−2). Therefore, the results reveal that the prepared densely functionalized membranes become good candidate proton exchange membrane materials for evaluation in fuel cell applications.

Microscopy Studies of the Novel Fluorinated Ionomers for Proton Exchange Membrane Fuel Cells

Perfluorosulfonic acid (PFSA) ionomers, such as Nafion, are widely used as a thin film on the Pt/C surface in the catalyst layers (CLs) in PEMFCs. They consist of polytetrafluoroethylene (PTFE) backbones and hydrophilic sulfonic acid group side-chains that facilitate the proton transport to the active sites in CLs. However, due to poor oxygen permeation through Nafion in CLs a new design of oxygen-permeable ionomers is required. In this regard, novel ionomers are synthesized by copolymerization of perfluoro-2,2-dimethyl-1,3-dioxole (PDD) with perfluoro(4-methyl-3,6-dioxaoct-7-ene) sulfonyl fluoride (PFSVE) and a ter-monomer. PDD and PSEPVE are providing improved oxygen permeability and ionic conductivity, respectively. PDD cathodes not only showed higher performance at high current densities than Nafion, but also better durability. In this work, the effect of the PDD content on the morphology and structures of the catalyst layer, before and after accelerated stress testing, was investigated through comprehensive characterization approaches. The PDD membrane electrode assemblies (MEAs) showed less catalyst layer thinning after 30K SWAST compared to Nafion. In contrast, PDD CLs displayed a considerable number of lateral cracks non-uniformly distributed, compared to the Nafion CLs, which could be due to the PDD’s different wetting properties during sample preparation. High PDD content in the CLs (62-68 mole%) resulted in the highest total porosity loss and Pt/Co change than low PDD content (24-36%), which was reflected in its highest performance loss among all the PDD MEAs. PDD cathodes also displayed lower particle size growth, lower Co loss, a lower degree of ionomer changes. In this talk we will discuss our characterization approach to determine a number of structural and compositional parameters, and correlate those findings with the performance and durability.

Highly efficient and selective aqueous aerobic oxidation of sulfides to sulfoxides or sulfones catalyzed by tungstate-functionalized nanomaterial

A Brönsted acidic ionic solid comrising tungstate-functionaized polyorganosiloxane framework (PMO-IL-WO42−) efficiently catalysed aerobic oxidation of sulfides in aqueous medium. The catalyst can selectively produce sulfoxides or sulfones by running the reaction at room temperature or 50 °C, respectively. Because of the ionic liquid-based charged surface containing hydrophobic organic functional groups and hydrophilic sulfonic acid group, the synergestic hydrophobic/hydrophilic and redox effect of PMO-IL-WO42- as water-friendly interfacial nanocatalyst simplifies and enhances the activity and selectivity toward the target sulfoxides or sulfones in water. Moreover, the PMO-IL-WO42- nanocatalyst exhibited outstanding stability and activity and can be recycled eight reaction runs without any significant activity and selectivity loss.

Synthesis of charged chitosan nanoparticles as functional biolubricant

Osteoarthritis has been a major disease in recent years, which is mainly related to the breakdown of the lubrication function of the cartilage sliding interface, along with the inflammation of the joint capsule. In this paper, one kind of novel biomimetic nanoparticles (NPs) lubricant, named CS-PS, is synthesized through chemically grafting hydrophilic sulfonic acid (SO3−) groups onto the surface of biocompatible and biodegradable chitosan (CS) NPs. Compared with control CS NPs, the as-synthesized CS-PS NPs exhibits excellent hydration and stability because of negatively charged surface zeta potential, along with extraordinary lubrication performance in water for realizing a super-low friction coefficient (COF) as ∼0.01 at the sliding interface of PDMS elastomer-Ti6Al4V disk. Correspondingly, the CS-PS NPs can also be used as a drug carrier for aspirin, which presents very good drug loading and release behavior in PBS (pH = 7.4). MCS cells culture experiment proves that this kind of novel lubricant is nontoxic and biocompatible, for which may be expected to use as potential articular injective material for the treatment of osteoarthritis.

Construction of graphene oxide membrane through non-covalent cross-linking by sulfonated cyclodextrin for ultra-permeable butanol dehydration

Two-dimensional (2D) lamellar graphene oxide (GO) membranes represent promising porous materials in alcohol dehydration. The separation performance can be manipulated by the physicochemical properties of interlayer channels. The relatively low flux and poor stability of GO-based membranes in aqueous environment are the major drawbacks. Herein, we intercalated a supramolecular compound, sulfobutyl-β-cyclodextrin (SCD), into the interlayer pores/channels of GO membranes. The sulfonic acid groups on SCD molecules are able to cross-link adjacent GO nanosheets throughnon-covalent interactions. The GO-SCD membranes possess excellent water affinity due to the presence of high hydrophilic sulfonic acid groups. For the n-butanol dehydration, the GO-SCD/PTFE membranes with well-defined interlayer pores exhibited ultrahigh permeation flux of 12955 g m-2 h-1 and separation factor of 1299 under 80 oC. The membranes remained stable in 144 h separation performance evaluation test and exhibited obviously enhanced thermal stability.

Tungstate ion (WO42-) confined in hydrophilic/hydrophobic nanomaterials functionalized brönsted acidic ionic liquid as highly active catalyst in the selective aerobic oxidation of alcohols in water

A Brönsted acidic Ionic Liquid containing tungstate anion functionalized polysiloxane network (PMO-IL-WO42-) was synthesized by simple self-condensation of tungstic acid and zwitterionic organosilane precursor possessing both imidazolium and sulfonate groups. Characterization by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), thermal gravimetric analysis TGA, nitrogen porosimetry, solid-state NMR spectroscopy and elemental analysis confirmed that both imidazolium cation and tungstate anion of zwitterion are successfully incorporated inside the organosilica framework. The catalytic activity of resulting hybrid PMO-IL- WO42- material was studied in the selective aerobic oxidation of primary and secondary alcohols using an atmospheric pressure of air in pure water. Due to the ionic liquid-based charged surface containing hydrophilic sulfonic acid and tungstate group, the synergistic hydrophilic/hydrophobic and redox effect of PMO-IL-WO42- as water-friendly catalyst facilitates and enhances the activity and selectivity toward the target oxidative products in water and proved to have a particularly broad substrate scope for reliable aerobic oxidation reaction. Furthermore, the catalyst showed outstanding stability and could be easily separated and reused at least ten reactions run under the same conditions as fresh catalyst without any loss of catalytic activity and product selectivity.

Nanometer-Scale Water Dynamics in Nafion Polymer Electrolyte Membranes: Influence of Molecular Hydrophobicity and Water Content Revisited.

The ionic conductivity of polymer electrolyte membranes (PEMs) is an essential parameter for their device applications. In water-swollen PEMs, protons and other ions are transferred through hydrophilic channels of a few nanometers in diameter at most. Thus, optimizing the chemical and physical properties of the channels can enhance the conductivity of PEMs. However, the factors controlling the conductivity have not been completely clarified. Here, we report that measurements taken near the channel walls by a special nuclear magnetic resonance technique with ≤1 nm spatial resolution showed the largest water diffusivity when ∼80% of hydrophilic sulfonic acid groups were blocked, but the proton conductivity was low. The water diffusivity was much less affected by differences in water content. Our results provide a concept for changing the properties of PEMs and a challenge to implement the improved diffusivity in a way that enhances net ion conductivity.

Modified walnut shell filter material for the enhanced removal of oil from oilfield wastewater

While polymer oil recovery greatly improves oil recovery, the polymer injected into the formation undergoes shearing, degradation, etc., and returns with the output liquid in the form of an anionic polyacrylamide of lower molecular weight, resulting in a production fluid. There is residual polymer, and this kind of polymer–containing wastewater is easy to contaminate the walnut shell filter in the sewage treatment process, resulting in failure of the walnut shell filter material, introduce hydrophilic sulfonic acid groups on the surface of the walnut shell filter material to lipophilic to hydrophilic of the surface. The dosage of NaHSO&lt;sub&gt;3&lt;/sub&gt; is 10-20% of the mass fraction of walnut shell filter (mass ratio %). Reflux reaction, and the reaction time was 1-5 h; the surface wettability of the walnut shell reversed. The surface contact angle drops from 95° before modification to 36.75°-66.25°, Its surface hydrophilic oleophobic performance has been significantly improved, Treatment of 150-230 mg/L of oily sewage, filtration and oil removal rate increased from 38.05% to 89.51% by modification; Backwashing and degreasing effect is increased by 4 times.

(Invited) Small Angle Scattering As Unique Probe to Quantify Water Distribution and Ionomer Structure in Operating PEMFC

The Proton Exchange Membrane Fuel Cell (PEMFC) is a highly complex energy conversion device coupling several electrochemical and transport phenomena occurring on a wide range of length-scales within a multilayered structure, named Membrane Electrodes Assembly (MEA). The fundamental description of all phenomena involved in PEMFC operation and degradation, and more particularly their interplay, is a contemplated pivotal requirement for improvements. This is a grand challenge, as a number of unsolved questions remain. In fact, all relevant physical and electrochemical phenomena are not fully identified or quantified. In the PEMFC, water plays a crucial role, since it is not only the main product of the electrochemical reaction but, above all, it is the fundamental common denominator to all the phenomena. In a real stack, as an open system converting H2 and O2, the operation and degradation are intrinsically heterogeneous resulting especially in a complex 3D distribution of water in the volume of the MEA. Among the most important component of the MEA is the ionomer, made of a PerFluoroSulfonic Acid (PFSA) polymer, which acts as a solid electrolyte to transfer proton and water to, from, and within the electrodes. The presence of highly hydrophilic sulfonic acid groups makes it, most probably, the most sensitive MEA component toward water activity/content. Indeed, it governs its swelling, structure as well as transport and mechanical properties. This property of the ionomer, along with its role, explains why PEMFC behaviour is so dependent on water activity. Still very recently, a work of Kongkanand et al.[1] emphasizes how ionomer is a crucial electrodes' constituent in view of enhancing performance. For these reasons, many researches are still devoted to studying the ionomer in relation with water activity and as well as to quantifying the 3D water distribution during PEMFC operation. It is well known that Small Angle Scattering (SAS) is the most suitable technique to characterize the structure of the ionomer[2]. A side from that, neutron is the probe of choice to quantify water within operating PEMFC[3]. For these reasons, we have been developing for several years SAS techniques, either with Neutrons or X-Ray, in order to measure simultaneously and operando, the water distribution and the ionomer nanostructure. Spatial and time resolutions offew µm² and 50 ms, respectively, have been achieved with the last generation of X-Rays sources such as the one of European Synchrotron Radiation Facility (ESRF), and ~4 mm² and 30 s with high neutron flux on D22 beamline at Laue Langevin Institute (ILL)[4],[5]. Thus, it is possible to follow the kinetics during transient. In particular, we have shown that, within the membrane, local water content is greater in front of the current collecting rib than in front of the gas supply channel. We have also evidenced some evolution of the physical structure of the membrane upon aging in real conditions depending on the local water content. We thus pushed forward these techniques, which now allows us to have unique information on the local water activity and ionomer structure within the CL. Our results demonstrate how SAS techniques are powerful to assess the main current scientific and technological issues of the PEMFC. [1] Kongkanand et al., ACS Energy Lett. 2018, 3, 618−621 [2] Fumagalli et al., J. Phys. Chem. B 2015, 119, 7068−7076 [3] Boillat et al., Current Opinion in Electrochemistry 2017, 5, 3–10 [4] Morin et al., J. Electrochem. Soc. 2016, 163, F9-F21 [5] Martinez et al., ACS Advanced Energy Materials 2019 Figure 1

Interesting Facets of Surface, Interfacial, and Bulk Characteristics of Perfluorinated Ionomer Films.

Ion-containing perfluorinated polymers possess unique viscoelastic properties, excellent proton conductivity, and nanophase-segregated structure all arising from the clustering of hydrophilic sulfonic acid groups within a matrix of hydrophobic fluorocarbons. When these ionomers are confined to nanothin films, a broad swathe of structural organization imparting a rich variety of surface, interfacial, and bulk characteristics can be expected. However, our understanding of perfluorinated ionomer thin film behavior is still in a rudimentary stage, and much of the research focus to date has been on its hydration-related structure and properties pertinent to electrochemical applications. Thus, many hidden gems-their interesting surface and interfacial properties-have been overlooked. In this Invited Feature Article, which is a summary of the key contributions by the author's group, including several collaborative publications on ionomer thin films, we unravel many of these facets. In addition, the article attempts to integrate knowledge acquired from a variety of investigations of different aspects of the ionomer thin films to refine and develop a consistent picture of their structure and behavior. First, we focus on the self-assembly of ionomers and show that dispersion media and hydrophobicity/hydrophilicity of the substrate can result in partial or even no coverage of substrates, shedding light on the complexity of polymer-substrate, polymer-solvent, and polymer-polymer interactions, an insight completely obscured when the spin-coating method is adopted for film creation. We demonstrate that the same ionomer can be used to create a variety of surfaces ranging from superhydrophilic to highly hydrophobic by controlling the film thickness or through the choice of substrate material. The ultrathin, hydrophilic surfaces of self-assembled Nafion ionomer films exhibit wettability switching behavior which opens the door to creating stimuli-responsive smart surfaces. The thermoresponsive behavior of the films is discussed in the context of surface (wettability) and bulk (thermal expansion) characteristics as well as a newly discovered vibrational mode. The substrate- and film thickness-dependent thermal expansion coefficients reinforce the importance of interfacial interactions and confinement on the structure/properties of these films. They also open up the potential of tuning ionomer bulk properties via substrate chemistry. The discovery of a vibrational mode that becomes thermally activated at high temperature has provided new insights into the origins of the molecular motions responsible for the α-relaxation of the Nafion ionomer as well as the underlying reason for wettability switching. Our recent neutron reflectometry study of different ionomers varying in side-chain composition/length on a platinum substrate shows that the interfacial hydration level is correlated to the side-chain length, which opens up the possibility of the controlling the interfacial electrochemistry. Finally, a systematic analysis of factors affecting proton conduction is presented to elucidate the yet-unresolved origins of the suppressed conduction of nanothin ionomer films compared to that of the bulk membrane. By revealing these interesting yet poorly understood facets of ionomer thin films, the article aims to stimulate further scientific pursuit on this topic.

Hollow Fiber Membranes of Blends of Polyethersulfone and Sulfonated Polymers.

Hollow fiber membranes (HFM) are fabricated from blend solutions of a polyethersulfone (PESU) with a sulfonated PESU (sPESU) or a sulfonated polyphenylenesulfone (sPPSU). The influence of different additives in the dope solution and different bore fluids on the HFM are studied. The addition of poly(sodium 4-styrene sulfonate) (PSSNa)/ethylene glycol (EG) to the dope solution results in an increased water flux of the HFM compared to its counterparts without this additive system. The morphology of the hollow fibers is examined by scanning electron microscopy (SEM). The inner surface of the hollow fibers is studied by X-ray photoelectron spectroscopy (XPS), and it is found that water permeation through the hollow fiber membranes is facilitated due to the change in morphology upon the addition of the PSSNa/EG additive system, but not by the presence of hydrophilic sulfonic acid groups on the membrane surface.

Functionalized carbon nanotubes for dispersive solid-phase extraction and atomic absorption spectroscopic determination of toxic metals ions

A nanosorbent for dispersive solid-phase extraction was fabricated by functionalizing multiwalled carbon nanotubes with sulfosalicylic acid after oxidation and thiolation followed by decoration with Fe3O4 nanoparticles. Incorporation of hydrophilic carboxylic and sulfonic acid groups introduces coordinating ability and accessibility for cadmium and lead, resulting in high sorption capacity of 217.39 and 454.54 mg g−1, respectively. Decoration by magnetic nanoparticles enhances its dispersibility and facilitates the separation of solid phase without tedious centrifugation or filtration processes, which is the exclusive objective of dispersive solid-phase extraction. The functionalized sorbent was characterized by FT-IR, SEM and TEM. The uniform and monolayer sorption behavior of the sorbent was proved by an evident fit of the equilibrium data to Langmuir isotherm model. The analytical method developed after optimizing the experimental variables such as solution pH, sorption time, amount of sorbent, desorption condition for preconcentration and separation enables the use of an economically viable less sensitive AAS for trace determination due to the improved detection limit of 0.13 and 1.21 µg L−1 for cadmium and lead, respectively. Commonly occurring concomitant ions in the real samples was not found to interfere in the trace determination of analyte. The good precision was assessed by the determined average day-to-day coefficient of variation of 3.02% for cadmium and 2.29% for lead. The accuracy and applicability of the present method for sequential cadmium and lead determination are substantiated by the analysis of Standard Reference Material and environmental water samples from electroplating industries, river water and tap water.

Improved electrical conductivity of poly(ethylene oxide) nanofibers using multi-walled carbon nanotubes

Highly conductive nanofibers with 1570 S/m were obtained from an electrospun solution of polymer containing multiwalled carbon nanotubes (MWCNTs). Homogeneous dispersion of high concentrations of MWCNTs was achieved by attaching poly(styrenesulfonic acid graft aniline) (PSS-g-ANI), an amphiphilic surfactant, to the MWCNT surface. The hydrophilic sulfonic acid group facilitated the dissolution of PSS-g-ANI-grafted MWCNTs in a polyethylene oxide (PEO) solution up to 6.7 wt% MWCNT. To our knowledge, this is the highest level of MWCNT doping attained in a solution designed for electrospinning. With the incorporation of PSS-g-ANI, the concentration of MWCNTs embedded in the electrospun nanofibers increased. More importantly, the alignment of MWCNTs along the nanofiber axis increased significantly, as confirmed by observed birefringence under crossed polarizers. The combination of higher doping levels and better alignment afforded highly conductive nanofibers suitable for electronic nanodevices.