Membrane Mechanical Stability Research Articles

Modulation of micro-rheological and hematological parameters in the presence of artificial carotid-jugular fistula in rats.

Arteriovenous fistula (AVF) may affect erythrocytes through many pathways (e.g., mechanical, inflammatory). However, these effects haven't been elucidated completely yet. To follow-up the hemorheological and the hematological changes in the presence of artificial carotid-jugular fistula in rats. Female Wistar rats were subjected to sham-operated group (SG, n = 6) and to fistula group (FG, n = 10). Under general anesthesia, the right carotid artery and jugular vein were isolated via a neck incision, and in the FG carotid-jugular fistula was performed by microsurgical techniques. Hematological variables, red blood cell (RBC) deformability and membrane (mechanical) stability parameters were determined before operation and on the 1st and 6th postoperative weeks. Density separated samples ('young' and 'old' RBCs) were also tested. In FG group hematocrit, RBC and platelet counts increased gradually to reach highly significant level of increment on the 6th postoperative week. RBC deformability significantly was impaired. The membrane stability test showed lower deformability values after applying mechanical shearing. No significant differences were observed between density separated RBC subpopulations. The presence of arteriovenous fistula may lead to an increment of RBC mass and impairment of RBC deformability. These changes could be one of the pathways through which the fistula influences the microcirculation.

Highly permeable Thermally Rearranged Mixed Matrix Membranes (TR-MMM)

Thermally Rearranged (TR) polymers and Mixed Matrix Membranes (MMMs) are two effective approaches used to advance the performance of gas separation membranes. Conversion of thermally activated groups in TR membranes result in hourglass-shaped cavities and unusually high permselectivity, whereas the inclusion of nanoparticles with engineered pore volume, window size and/or surface chemistry in MMMs can add fast and selective pathways for gas transport. In this study, we explored the effects of combining these two approaches by adding ultra-porous and highly thermostable PAF-1 nanoparticles into the TR-able polymer, 6FDA-HAB5DAM5 (DAM). Gas separation performances of TR-MMMs were evaluated by comparison with the pure polymer and another TR-MMM bearing an already thermally-treated PAF-1 additive (cPAF). While both additives enhanced gas transport, only PAF-1 stabilized the TR conversion reaction and improved the TR-MMM's material properties. Minor variations in cPAF surface changed the TR-MMM interfacial interactions as well as other properties crucial to the application of advanced membrane materials, namely aging, plasticization, and mechanical stability. By combining thermal rearrangement process with PAF-1, TR-MMM demonstrated a 55-fold increase in CO2 gas permeability (37-fold for H2) at similar gas selectivities, but without the handling issues observed for the pure TR polymer membrane.

(Invited) U.S. DOE Early-Stage Alkaline Membrane Fuel Cell R&D

The U.S. Department of Energy (DOE) supports research, development, and demonstration of fuel cell technologies for transportation, stationary, and crosscutting applications. Applied, early-stage fuel cell research and development (R&D) efforts predominantly focus on stack materials and components to achieve low-cost, high performance fuel cell systems, and include longer term technologies, such as alkaline membrane fuel cells (AMFCs). More favorable oxygen reduction kinetics and increased platinum group metal (PGM)-free catalyst stability at high pH conditions have invigorated interest in alkaline membrane fuel cells as an alternative to polymer electrolyte membrane fuel cells (PEMFCs), on which fuel cell electric vehicles currently available for retail sale are based. The catalyst accounts for >40% of the projected high-volume stack cost in PEMFC electric vehicles, owing largely to the inclusion of PGMs [1]. Achieving cost competitiveness with internal combustion engine vehicles could be expedited by eliminating PGM-based catalysts; AMFCs offer a promising route for successfully incorporating state of the art PGM-free catalysts into membrane electrode assemblies (MEAs). In addition, improved alkaline exchange membranes (AEMs) have crosscut benefits to applications beyond fuel cells, including electrolysis for hydrogen production and reversible fuel cells. Alkaline membrane R&D is targeted to increase conductivity over a wider range of operating temperature and relative humidity and to increase membrane mechanical, chemical, and thermal stability with diminished fuel crossover. In 2016, an expert-led workshop on AEMs was convened by the DOE based on intense interest in the field [2]. There was consensus on the need for AEM-specific standardized protocols and testing and for further improvement in MEA performance. Furthermore, the profound lack of readily available, stable AEMs or ionomers for high pH MEAs must be addressed in order to expand entry into the field and foster more rapid progress in AMFC development. In order to increase coordination in the polymer electrolyte membrane community (including AEMs) to accelerate R&D success in fuel cells and other devices (electrolyzers, redox flow batteries, etc.), the FCTO has recently organized the National Laboratory-led Membranes Working Group. Stable, conductive polymer materials and durable hydrogen oxidation catalysts are key to realizing commercially relevant AMFCs. This presentation will highlight recent advancements in AMFCs in the DOE R&D portfolio include increasing performance and durability in perfluorinated and hydrocarbon-based ionomers, increasing cation group stability, diminishing catalyst deactivation due to ionomer-catalyst interaction, and PGM-free MEA performance of 350 mW/cm2. This presentation will also provide an outlook on future activities.

Cells Adhering to 3D Vertical Nanostructures: Cell Membrane Reshaping without Stable Internalization.

The dynamic interface between the cellular membrane and 3D nanostructures determines biological processes and guides the design of novel biomedical devices. Despite the fact that recent advancements in the fabrication of artificial biointerfaces have yielded an enhanced understanding of this interface, there remain open questions on how the cellular membrane reacts and behaves in the presence of sharp objects on the nanoscale. Here we provide a multifaceted characterization of the cellular membrane's mechanical stability when closely interacting with high-aspect-ratio 3D vertical nanostructures, providing strong evidence that vertical nanostructures spontaneously penetrate the cellular membrane to form a steady intracellular coupling only in rare cases and under specific conditions. The cell membrane is able to conform tightly over the majority of structures with various shapes while maintaining its integrity.

(Invited) U.S. DOE Early-Stage Alkaline Membrane Fuel Cell R&D

The U.S. Department of Energy (DOE) supports research, development, and demonstration of fuel cell technologies for transportation, stationary, and early market applications. Fuel cell research and development (R&D) efforts predominantly concentrate on R&D of fuel cell stack materials and components to achieve low-cost, high performance fuel cell systems, and include longer term technologies, such as alkaline membrane fuel cells (AMFCs). More favorable oxygen reduction kinetics and increased platinum group metal (PGM)-free catalyst stability at high pH conditions have invigorated interest in alkaline membrane fuel cells as an alternative to polymer electrolyte membrane fuel cells (PEMFCs), on which fuel cell electric vehicles currently available for retail sale are based. The catalyst accounts for >40% of the projected high-volume stack cost in PEMFC electric vehicles, owing largely to the inclusion of PGMs [1]. Achieving cost competitiveness with internal combustion engine vehicles will be expedited by eliminating PGM-based catalysts; AMFCs offer a promising route for successfully incorporating state of the art PGM-free catalysts into membrane electrode assemblies (MEAs). Alkaline membrane R&D is targeted to increase the operating temperature and humidity ranges of fuel cells while improving conductivity and to increase membrane mechanical, chemical, and thermal stability with diminished fuel crossover. In 2016, an expert-led workshop on alkaline electrolyte membranes (AEMs) was convened by the DOE based on intense interest in the field and recent advances including performance of >1 W/cm2 in H2/O2 MEA testing [2]. There was consensus on the need for AEM-specific standardized protocols and testing and for further improvement in MEA performance. In order to accelerate materials development within the field, the DOE has set an AMFC-specific 2020 technical milestone of PGM-free MEA demonstration of >600 mW/cm2 performance in H2/air. Stable, conductive polymer materials and durable hydrogen oxidation catalysts are key to realizing commercially relevant AEMFCs. Existing efforts in the DOE R&D portfolio include increasing performance and durability in perfluorinated and hydrocarbon-based ionomers, increasing cation group stability, diminishing catalyst deactivation due to ionomer-catalyst interaction, and PGM-free MEA performance of 350 mW/cm2. Going forward, the profound lack of readily available, stable AEMs or ionomers for high pH MEAs must be addressed in order to expand entry into the field and foster more rapid progress in AEMFC development.

Imidazolium-Based Grafted Anion Exchange Membranes: Interplay between the Morphology and Anion Transport Behavior

Anion-exchange membranes (AEMs) have been regarded as an alternative to proton-exchange membranes (PEMs) in energy conversion devices, due to the advantage of saving expensive platinum catalysts. However, neither the molecular design nor the property understanding is sufficient for developing AEMs capable of practical fuel cell applications. It is crucial to thoroughly study the current AEMs in terms of microphase structures and conducting properties. Recently, we developed a new graft type of AEMs by radiation-induced grafting method, where imidazolium and styrene monomers were grafted into poly(ethylene-co-tetrafluoroethylene) (ETFE) base films under a dose of 80 kGy from the 60Co γ-ray source (QST, Takasaki), followed by alkylation and ion exchange reactions. These AEMs exhibit well-balanced properties of high ion conductivity (> 100 mS/cm at 80oC) and good stability, which are believed to be controlled by the microphase structure of the membrane. In this report, we investigate the memrbane structure and reveal the relationship between structure and properties, using small-angle neutron scattering (SANS) method. Fig. 1 shows typical SANS intensity profiles, I(q), of pristine ETFE films (profile 1), grafted-ETFE membranes (profile 2), dry AEM (profile 3) and AEM equilibrated in D2O (profile 4) as a function of scattering vector q. The different morphologies which can be deduced from the SANS profiles are also shown in the figure. The experiments confirm the semi-crystalline feature of AEM conserved from the original ETFE base film, which is the key factor for the high membrane mechanical stability, and show the dependence of the structure on hydration. Contrast variation experiments performed on AEM equilibrated in water mixtures of H2O and D2O, further show that graft polymers and water consist the hydrophilic ion channels [1]. Since graft polymers distribute randomly in AEM, well-connected hydrophilic ion channels are feasibly formed, which is the key factor for the high membrane conductivity. Above all, the interplay between the morphology and properties can be characterized as follows: 1) semi-crystalline base film offers good mechanical properties; 2) graft polymers and water form ion channels to promote the conductivity. Figure 1

Phosphonium-Based Poly(ionic liquid)/Ionic Liquid Ion Gel Membranes: Influence of Structure and Ionic Liquid Loading on Ion Conductivity and Light Gas Separation Performance

The influence of free IL structure and loading level in phosphonium-based poly(ionic liquid)/ionic liquid (PIL/IL) ion gel composite membranes was studied with regards to their ion conductivity and light gas separation performance. The resulting series of ion gels demonstrated ion conductivity values of 10–7–10–5 S/cm at 25 °C and 10–5–10–3 S/cm at 110 °C. It was found that shorter alkyl chain lengths on the phosphonium cation of the IL resulted in increased thermal stability of the ionic conductivity for the resulting PIL/IL membrane materials with negligible changes in ionic conductivity performance at temperatures up to 110 °C. Further, an increase of free IL loading resulted in an increase in overall ion conductivity and membrane mechanical stability. Similar structure/composition/function relationships were observed for the light gas separation performance of these phosphonium-based PIL/IL ion gel membranes. However, the resulting performance is lower than PIL/IL ion gel membranes based on imidazoliu...

Optimization of polyethylene binder for heterogeneous ion exchange membrane manufacture to improve its mechanical stability

ABSTRACTAim of this work is to propose polymer mixture for heterogeneous ion exchange membrane manufacture to improve membrane mechanical stability. Polyethylene (PE) binders [high‐density PE (HDPE), linear low‐density PE (LLDPE), metallocene‐linear low‐density PE (mLLDPE), and their mixtures in various ratios] with ion exchange resins were homogenized and extruded into membrane sheets. Processability of mixtures was considered using the data from extruder including torque and pressure before the extrusion die. Membrane samples were subjected to tensile deformation tests and tests of tear resistance and membrane electrochemical properties such as electrical resistance and permselectivity were measured. No significant variations in electrochemical properties of prepared membranes were observed, except of membrane made using pure mLLDPE as a binder. Surface resistance of this membrane was the highest (almost 8 Ω cm2) and as well the permselectivity (∼92%). The lowest surface resistance (lower than 3 Ω cm2) was determined for the membrane made using pure LLDPE as a binder. Therefore, taking into account the most important mechanical and processing characteristics, such as pressure before extrusion die, tensile strength, modulus of elasticity, and tear resistance assigning all these properties the same priority, membrane with the best combination of properties was prepared using the mixture of HDPE:LLDPE in the ratio of 80:20 as the binder. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2018,135, 46415.

Temperature induced lipid membrane restructuring and changes in nanomechanics

The naturally occurring milk sphingomyelin is of particular interest owing to its complex composition and involvement in the formation of the milk fat globule membrane (MFGM). Knowledge of membrane organization and nanomechanical stability has proved to be crucial in understanding their properties and functions. In this work, two model membrane systems composed of 1, 2 dioleoyl-sn-glycero-3-phosphocholine (DOPC), egg sphingomyelin (egg-SM) and cholesterol, and DOPC, milk sphingomyelin (milk-SM) and cholesterol were exposed to both RT and 10°C. The morphological and nanomechanical changes were investigated using atomic force microscopy (AFM) imaging and force mapping below RT using a designed liquid cell with temperature-control. In both systems, the size and shape of SM/Chol-enriched liquid ordered domains (Lo) and DOPC-enriched liquid disordered phase (Ld) were monitored at controlled temperatures. AFM based force-mapping showed that rupture forces were consistently higher for Lo domains than Ld phases and were decreased for Ld with decreasing temperature while an increase in breakthrough force was observed in Lo domains. More interestingly, dynamic changes and defect formations in the hydrated lipid bilayers were mostly detected at low temperature, suggesting a rearrangement of lipid molecules to relieve additional tension introduced upon cooling. Noteworthy, in these model membrane systems, tension-driven defects generally heal on reheating the sample. The results of this work bring new insights to low temperature induced membrane structural reorganization and mechanical stability changes which will bring us one step closer to understand more complex systems such as the MFGM.

Impact of sodium hypochlorite cleaning on the surface properties and performance of PVDF membranes

Abstract The adverse effect of sodium hypochlorite (NaClO) cleaning has raised concerns regarding their potential impacts on the membrane materials and activated sludge. In this study, the effect of NaClO cleaning on the physicochemical properties, surface free energy, and fouling propensity of polyvinylidene fluoride (PVDF) membranes was systematically investigated. The Analysis of Variance showed that the variation of NaClO soaking time had a significant effect on the permeability and hydrophilicity of PVDF membranes, while effects of NaClO concentration were insignificant. Results showed that the chemical cleaning with NaClO led to a reduction of membrane mechanical strength, which meant the potential harmful impact on the mechanical stability of membranes. The extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory analysis results showed that the electron donor components (γ−) of membrane surfaces decreased and the electron acceptor components (γ+) relatively increased with the extension of NaClO exposure time, which facilitated membrane fouling propensity.

Poly(arylene ether ketone) with pendant pyridinium groups for alkaline fuel cell membranes

Using the step-growth polycondensation reaction, poly(arylene ether ketone) (PAEK) and activated poly(arylene ether ketone)-NHS intermediates (PAEK-N) were synthesized. PAEK-NHS intermediates with pyridinium groups (PAEK-PYR) were obtained by adding different amounts of PYR groups. The successful syntheses of PAEK, PAEK-N, and PAEK-PYR were confirmed by nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy. Several important membrane properties (e.g., ionic exchange capacity (IEC), water uptake, anion conductivity, and thermal and mechanical stability) were investigated for their applications in alkaline fuel cells. Water uptake, swelling ratio, anion conductivity, and IEC increased with increasing PYR contents, while the mechanical properties decreased. Among a series of prepared membranes, the PAEK-PYR100 and PAEK-PYR125 membranes showed IEC and anion conductivity values that were higher than those of a commercial AHA membrane. Also, all of the prepared membranes were thermally stable up to 255 °C and show excellent chemical stability in alkaline conditions.

Reversible binding of hemoglobin to band 3 constitutes the molecular switch that mediates O2 regulation of erythrocyte properties

AbstractFunctional studies have shown that the oxygenation state of the erythrocyte regulates many important pathways, including glucose metabolism, membrane mechanical stability, and cellular adenosine triphosphate (ATP) release. Deoxyhemoglobin (deoxyHb), but not oxyhemoglobin, binds avidly and reversibly to band 3, the major erythrocyte membrane protein. Because band 3 associates with multiple metabolic, solute transport, signal transduction, and structural proteins, the hypothesis naturally arises that the O2-dependent regulation of erythrocyte properties might be mediated by the reversible association of deoxyHb with band 3. To explore whether the band 3–deoxyHb interaction constitutes a “molecular switch” for regulating erythrocyte biology, we have generated transgenic mice with mutations in the deoxyHb-binding domain of band 3. One strain of mouse contains a “humanized” band 3 in which the N-terminal 45 residues of mouse band 3 are replaced by the homologous sequence from human band 3, including the normal human band 3 deoxyHb-binding site. The second mouse contains the same substitution as the first, except the deoxyHb site on band 3 (residues 12-23) has been deleted. Comparison of these animals with wild-type mice demonstrates that the following erythrocyte properties are controlled by the O2-dependent association of hemoglobin with band 3: (1) assembly of a glycolytic enzyme complex on the erythrocyte membrane which is associated with a shift in glucose metabolism between the pentose phosphate pathway and glycolysis, (2) interaction of ankyrin with band 3 and the concomitant regulation of erythrocyte membrane stability, and (3) release of ATP from the red cell which has been linked to vasodilation.

Zeolite ZSM5-Filled PVDF Hollow Fiber Mixed Matrix Membranes for Efficient Carbon Dioxide Removal via Membrane Contactor

ZSM5 zeolite-filled PVDF mixed matrix membranes (MMMs) were wet spun and used for CO2 absorption in a contactor system. The properties of ZSM5 were analytically characterized. SEM images revealed the fully asymmetric structure of membranes, in which the creation of finger-like macrovoids was promoted with increasing filler loading. A significant increase in gas permeance was observed, which was associated with the porosity increase of the membrane surface despite the decrease in surface pore size. The surface roughness, wettability resistance, and mechanical stability of membranes were also considerably improved by filler loading. A CO2 absorption test with water revealed a higher CO2 flux of MMMs than that of the plain membrane. Peak absorption flux of 5.80 × 10–3 mol m–2 s–1 was achieved at a liquid velocity of 1.2 m s–1 for 5 wt % ZSM5/PVDF membrane (MZ5), which was nearly 177% higher than that of neat PVDF and also surpassed that of several commercial and in-house made membranes. The mass transfer res...

Evaluation of Electrochemical Properties, Study of Chemical and Mechanical Stability Supported with Ionic Transport and Surface Charge Density Mechanism of PVC Based Cobalt Tungstate Cation Exchange Membrane

The chemical and mechanical stability of membrane play a important role for understanding the mechanism and applications of cobalt tungstate cation exchange membrane. The PVC based cobalt tungstate (CT) membrane has been prepared by different methods like sol-gel, die-casting and others material processing techniques. It has been prepared through the mixing of PVC with cobalt tungstate into a definite ratio (1:3) that shows good mechanical stability. Moreover, the paper is concerned with physico-chemical and electro-chemical characterization of membrane, namely fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical studies. The results of characterization and electrochemical studies offered the potential industrial applications of membrane in different areas.

Atomic layer deposition of TiO2 film on a polyethersulfone membrane: separation applications

In the current study, a titanium dioxide (TiO2) nanostructured film was grown on a polyethersulfone (PES) substrate membrane using atomic layer deposition (ALD) with the aim of tailoring the membrane surface properties to be suitable for desalination applications. Scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle (CA) and zeta potential measurements and a tensile meter were used to characterize the membrane morphology, surface properties and mechanical stability, respectively. In addition, the separation performance of all of the prepared membranes was evaluated in terms of water flux and salt rejection. The results showed that the TiO2 nanostructured film deposited-PES membrane exhibited excellent performance with a rejection of ≥90 % at room temperature for NaCl, which is four times greater than that of a PES membrane alone. It is interesting to note that the deposition of the TiO2 film resulted in a marginal decrease in the water flux from 60 ± 2 Lm−2 h−1 to 47 ± 2 Lm−2 h−1 of the resulting membrane due to the TiO2 film’s nanometre-scale thickness. Moreover, the ALD of the TiO2 film enhanced the mechanical strength of the membrane as it tightly wrapped the skeleton of the membrane.

Investigation of Humidity Dependent Surface Morphology and Proton Conduction in Multi-Acid Side Chain Membranes by Conductive Probe Atomic Force Microscopy.

In this report, we employ phase-contrast tapping mode and conductive probe atomic force microscopy (cp-AFM) as tools to investigate the nanoscale morphology and proton conductance of a 3M perfluoro-imide acid (PFIA) membrane (625 EW) over a large range of relative humidity (3-95% RH). As a point of comparison, we also investigate 3M perfluorosulfonic acid (PFSA) (825 EW) and Nafion 212. With AFM, we assess the membrane's water retention and mechanical stability at low RH and high RH, respectively. Cp-AFM allows us to spatially resolve the hydrophilic and electrochemically active domains under a similar set of conditions and observe directly the ties between membrane morphology and proton conductance. From our data, we are able to correlate the improved water retention indicated by the size of the hydrophilic domains with the proton conductance in the PFIA membrane at elevated temperature and compare the result with that observed for the PFSA and Nafion. At high RH conditions, we see evidence of a nearly continuous hydrophilic phase, which indicates a high degree of swelling.

Characterization of Butanediol-Alginate Ester as Candidate of Hemodialysis Membrane

An ester of butanediol-alginate has been studied as a possible hemodialysis membrane. With 1,4-butanediol molar ratio of 0.1, 0.5, and 1.0, it showed that the membrane mechanical properties, stability, protein adsorption, platelet adhesion and performance for urea and creatinine clearance are better than that of unmodified alginate. The increase in 1,4-butanediol molar ratio causes hemodialysis ratio to improve, and causes protein adsorption and platelet adhesion at the membrane surface to decrease. In the case of protein adsorption and platelet adhesion, the membrane with the molar ratio of 1.0 has better hemocompatibility properties. In the hemodialysis test for 4 h, using 2.742 mg cm-2 h-1 of urea and 0.058 mg cm-2 h-1 of creatinine flux, this membrane showed that 48.5% of urea and 44.2% of creatinine were cleaned.

Abnormal erythroid maturation leads to microcytic anemia in the TSAP6/Steap3 null mouse model.

Genetic ablation of the ferrireductase STEAP3, also known as TSAP6, leads to severe microcytic and hypochromic red cells with moderate anemia in the mouse. However, the mechanism leading to anemia is poorly understood. Previous results indicate that TSAP6/Steap3 is a regulator of exosome secretion. Using TSAP6/Steap3 knockout mice, we first undertook a comprehensive hematologic characterization of the red cell compartment, and confirmed a dramatic decrease in the volume and hemoglobin content of these erythrocytes. We observed marked anisocytosis as well as the presence of fragmenting erythrocytes. Consistent with these observations, we found by ektacytometry decreased membrane mechanical stability of knockout red cells. However, we were unable to document significant changes in the expression levels of the major skeletal and transmembrane proteins to account for this decrease in the membrane stability. Furthermore, there were no differences in red cell survival between wild type and knockout animals. However, when we monitored erythropoiesis, we found a decreased number of proerythroblasts in the bone marrow of TSAP6/Steap3(-/-) animals. In addition, progression from the proerythroblastic to the orthochromatic stage was affected, with accumulation of cells at the polychromatic stage. Altogether, our findings demonstrate that abnormal erythroid maturation is the main cause of anemia in these mice.

Novel nanocomposite heterogeneous cation exchange membrane prepared by MWCNTs-co-silver nanolayer composite nanoparticles: Physico/chemical characterization and investigation of concentration effect

Nanocomposite polyvinyl chloride/multi walled carbon nano tubes (MWCNTs)-co-silver (Ag) nanolayer composite nanoparticles heterogeneous ion exchange membranes were prepared by solution casting techniques. MWCNTs-co-Ag nanolayer composite nanoparticles were prepared by magnetron sputtering method. The effect of used composite nanoparticles and electrolyte’s concentration on physico/chemical properties of membranes was studied. Scanning and transmission electron microscopy and X-ray diffraction results showed uniform distribution and crystalline structure for the composite nanoparticles. Images also showed relatively uniform distribution for the membranes. Membrane transport number, selectivity and electrical conductivity were improved by increase of additive content in membrane matrix. All mentioned parameters were also enhanced by increase of electrolyte concentration. Membranes exhibited lower selectivity/transport number for bivalent ions compared to monovalent type. Membrane average roughness was decreased slightly by increase of additive content. Membrane ionic flux was decreased initially by increase of additive content up to 0.5%wt and then began to increase by more additive concentration. Mechanical stability of membranes was also improved by using of composite nanoparticles in membrane matrix. Modified membrane containing 4%wt composite nanoparticles showed better electrochemical properties compared to others.

PVDF membrane biofunctionalization by chemical grafting

The objective of the work was to develop a suitable method for covalent immobilization of labile active biomolecules on inert hydrophobic polyvinylidene fluoride (PVDF) membrane, preserving both membrane stability and biomolecule activity. PVDF is advantageous over other membrane materials due to its high mechanical strength and excellent chemical resistance. On the other hand, its native structure does not have sites for biomolecules covalent immobilization in mild conditions. The strategy of the present work consisted in grafting reactive groups on the hydrophobic PVDF to which attaching functional groups able to covalently bound biomolecules in mild conditions. Tuning grafting conditions were crucial in order to attack the inert membrane while maintaining suitable membrane chemical and mechanical stability. Therefore, surface modification of native PVDF flat-sheet membranes was performed by wet chemical strategy, under basic conditions, using 1,5-diamino-2-methylpentane (DAMP) as carrier of amino groups. Afterwards, these groups were activated with glutaraldehyde (GA) to which biomolecules were easily attached by covalent bond. Two model proteins having different properties (BSA and Lipase) were selected for immobilization test. DAMP concentration, reaction temperature, and reaction time were studied in order to tune both the degree of modification and the loading capacity of the functionalized membrane taking in account the mechanical stability of the membrane. Modified and native PVDF membranes were characterized by Fourier transform infrared spectroscopy (FT-IR), the ninhydrin test, scanning electron microscopy (SEM) and the mechanical resistance test. Enzymatic activity of immobilized lipase was tested in a biphasic systems using the hydrolysis of triglycerides as model reaction.Modified membranes showed higher binding capacities compared with unmodified PVDF membrane. Optimal conditions for grafting reactive amino groups able to guarantee membrane stability and enzyme loading suitable to achieve good enzyme specific activity were identified.