Preparation and hydrogen permeation of SrCe0.95Y0.05O3−δ asymmetrical membranes

Asymmetrical thin membranes of SrCe_0.95Y_0.05O_3−δ (SCY) were prepared by a conventional and cost-effective dry pressing method. The substrate consisted of SCY, NiO and soluble starch (SS), and the top layer was the SCY. NiO was used as a pore former and soluble starch was used to control the shrinkage of the substrate to match that of the top layer. Crack-free asymmetrical thin membranes with thicknesses of about 50 μm and grain sizes of 5–10 μm were successfully pressed on to the substrates. Hydrogen permeation fluxes (J_H2) of these thin membranes were measured under different operating conditions. At 950 °C, J_H2 of the 50 μm SCY asymmetrical membrane towards a mixture of 80% H₂/He was as high as 7.6 × 10⁻⁸ mol/cm² s, which was about 7 times higher than that of the symmetrical membranes with a thickness of about 620 μm. The hydrogen permeation properties of SCY asymmetrical membranes were investigated and activation energies for hydrogen permeation fluxes were calculated. The slope of the relationship between the hydrogen permeation fluxes and the thickness of the membranes was −0.72, indicating that permeation in SCY asymmetric membranes was controlled by both bulk diffusion and surface reaction in the range investigated.     

Preparation and pervaporation performance of surface crosslinked PVA/PES composite membrane

This study describes the facile preparation of poly(vinyl alcohol) (PVA)/polyethersulfone (PES) composite membranes by interfacial reaction technique, aiming at acquiring the improved structural and operational stability of the resulting membranes. The effect of interfacial crosslinking agent and hydrophilicity of support layer on the interfacial adhesive strength and pervaporation performance of composite membranes were investigated. The optimal recipe for PVA/PES composite membrane preparation was as follows: PES support layer was treated with 0.1 wt.% borax aqueous solution, fully dried and then immersed into 2 wt.% PVA aqueous solution. The resulting PVA active layer was 1–1.5 μm thick after twice dip-coating. The as-prepared PVA/PES composite membrane exhibited high separation factor of over 438, high permeation flux of 427 g m⁻² h⁻¹ for 80 wt.% EG in the feed at 70 °C and desirable structural stability. It could be derived that adoption of interfacial reaction would be an effective method for preparing the composite membranes suitable for large-scale dehydration of ethylene glycol/water mixture.     

Microbubble formation using asymmetric Shirasu porous glass (SPG) membranes and porous ceramic membranes—A comparative study

We have recently proposed a new method for generating uniformly sized microbubbles from Shirasu porous glass (SPG) membranes with a narrow pore size distribution. In this study, to obtain a high gas permeation rate through SPG membranes in microbubble formation process, asymmetric SPG membranes were used. At the transmembrane/bubble point pressure ratio of less than 1.50, uniformly sized microbubbles with a bubble/pore diameter ratio of approximately 9 were generated from an asymmetric SPG membrane with a mean pore diameter of 1.58 μm and a skin-layer thickness of 12 ± 2 μm at a gaseous-phase flux of 2.1–24.6 m³ m⁻² h⁻¹, which was much higher than that through a symmetric SPG membrane with the same pore diameter. This is mainly due to the much smaller membrane resistance of the asymmetric SPG membrane. Only 0.27–0.43% of the pores of the asymmetric SPG membrane was active under the same conditions. The proportion of active pores increased with a decrease in the thickness of skin layer. In contrast to the microbubble formation from asymmetric SPG membranes, polydispersed larger bubbles were generated from asymmetric porous ceramic membranes used in this study, due to the surface defects on the skin layer. The surface defects were observed by the scanning electron microscopy and detected by the bubble point method.     

Proton and methanol transport behavior of SPEEK/TPA/MCM-41 composite membranes for fuel cell application

This paper reports proton and methanol transport behavior of composite membranes prepared for use in the direct methanol fuel cell (DMFC). The composite membranes were prepared by embedding various proportions (10–30 wt.%) of inorganic proton conducting material (tungstophosphoric acid (TPA)/MCM-41) into sulfonated poly(ether ether ketone) (SPEEK) polymer matrix. The results indicate that the proton conductivity of the membranes increases with increasing loading of solid proton conducting material. The highest conductivity value of 2.75 mS/cm was obtained for the SPEEK composite membrane containing 30 wt.% solid proton conducting material (50 wt.% TPA in MCM-41). The methanol permeability and crossover flux were also found to increase with increasing loading of the solid proton conducting material. Lowest permeability value of 5.7 × 10⁻⁹ cm² s⁻¹ was obtained for composite membrane with 10 wt.% of the solid proton conducting material (40 wt.% TPA in MCM-41). However, all the composite membranes showed higher selectivity (ratio between the proton conductivity and the methanol permeability) compared to the pure SPEEK membrane. In addition, the membranes are thermally stable up to 160 °C. Thus, these membranes have potential to be considered for use in direct methanol fuel cell.     

A study on the interactions of Aurein 2.5 with bacterial membranes

Aurein 2.5 (GLFDIVKKVVGAFGSL-NH₂) is an uncharacterised antimicrobial peptide. At an air/water interface, it exhibited strong surface activity (maximal surface pressure 25 mN m⁻¹) and molecular areas consistent with the adoption of α-helical structure orientated either perpendicular (1.72 nm² molecule⁻¹) or parallel (3.6 nm² molecule⁻¹) to the interface. Aurein 2.5 was strongly antibacterial, exhibiting a minimum inhibitory concentration (MIC) of 30 μM against Bacillus subtilis and Escherichia coli. The peptide induced maximal surface pressure changes of 9 mN m⁻¹ and 5 mN m⁻¹, respectively, in monolayers mimicking membranes of these organisms whilst compression isotherm analysis of these monolayers showed ΔG_Mix > 0, indicating destabilisation by Aurein 2.5. These combined data suggested that toxicity of the peptide to these organisms may involve membrane invasion via the use of oblique orientated α-helical structure. The peptide induced strong, comparable maximal surface changes in monolayers of DOPG (7.5 mN m⁻¹) and DOPE monolayers (6 mN m⁻¹) suggesting that the membrane interactions of Aurein 2.5 were driven by amphiphilicity rather than electrostatic interaction. Based on these data, it was suggested that the differing ability of Aurein 2.5 to insert into membranes of B. subtilis and E. coli was probably related to membrane-based factors such as differences in lipid packing characteristics. The peptide was active against both sessile E. coli and Staphylococcus aureus with an MIC of 125 μM. The broad-spectrum antibacterial activity and non-specific modes of membrane action used by Aurein 2.5 suggested use as an anti-biofilm agent such as in the decontamination of medical devices.     

Performance improvement of polysulfone ultrafiltration membrane by blending with polyaniline nanofibers

Polyaniline (PANI) nanofibers were used to improve hydrophilic property and permeability of polysulfone (PS) membrane. PS membrane and PS/PANI nanofibers blended membranes with different PANI–PS mass ratios (1, 5, 10, and 15 wt.%) were prepared by phase inversion process. The blended membranes showed similar bovine serum albumin (BSA) and albumin egg (AE) rejections to PS membrane. The blended membranes had larger porosity and better hydrophilic property than PS membrane, which caused the improvement of their permeability. Pure water fluxes of the blended membranes with PANI–PS mass ratios of 1 and 15 wt.% were 1.6 and 2.4 times that of PS membrane, respectively. During the filtration of BSA solution, the blended membranes had slower flux decline rate than PS membrane. Moreover, stable permeate fluxes of the blended membranes with PANI–PS mass ratios of 1 and 15 wt.% were 2.0 and 2.5 times that of PS membrane, respectively. Compared with PS membrane, mechanical property and thermal stability of the blended membranes with less PANI–PS mass ratio, e.g. 1 wt.%, had no obvious change. For the blended membrane with PANI–PS mass ratio of 15 wt.%, breaking strength increased 28% and elongation at break decreased 30.6%.     

Real-time monitoring of metal deposition and segregation phenomena during preparation of PdCu membranes

The N₂ and H₂ evolution, respectively, were monitored during deposition of Pd and Cu from electroless plating baths to obtain in-process control of the composition during preparation of 3–7 μm thick PdCu membranes on tubular ceramic substrates. Compositions estimated by gas evolution compare favorably to those measured in post-mortem XRD and EDS analyses, mostly differing by not more than 1 at.%. This result suggests that use of gas evolution measurements to enable in-process control of composition to within 1 at.% is feasible. Annealing experiments in an H₂ atmosphere demonstrated that, at 893 K, only 48 h are needed to form a stoichiometrically homogeneous, 9.5 μm thick, face centered cubic (fcc) Pd₆₃Cu₃₇ membrane from sequentially deposited layers; at 723 K, the same transformation requires over 2 weeks. The appearance of transient body centered cubic (bcc) and fcc phases with lower Pd contents signaled compositional segregation in the initial stages of alloy formation at 723 and 773 K and could be a source of persistent stoichiometric heterogeneity particularly in bcc PdCu membranes. The H₂ fluxes of fcc Pd₅₈Cu₄₂ and Pd₇₀Cu₃₀ membranes were J_H2=(1.6±1.1) mol m⁻² s⁻¹ exp[(−24.8±0.4)kJ mol⁻¹/RT] and J_H2=(3.7±0.6) mol m⁻² s⁻¹ exp[(−21.3±1.0)kJ mol⁻¹/RT], respectively, at 100 kPa H₂ pressure difference.     

Preparation and characterisation of novel polysulfone membranes modified with Pluronic F-127 for reducing microalgal fouling

In this study, hydrophilic and fouling-resistant polysulfone (PS) membranes were fabricated using the phase inversion method to reduce membrane fouling caused by microalgal culture. The Pluronic F-127 polymer, which is used as a hydrophilic co-polymer, was added to the membranes to improve the membrane properties. Characteristic specifications of the fabricated membranes, such as morphology, surface roughness, chemical structures and hydrophobicity/hydrophilicity, were studied using scanning electron microscopy, atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDS), attenuated total reflection-fourier infrared (ATR-FTIR) spectroscopy and contact angle devices. According to the results obtained, it was observed that, with the increase of the Pluronic F-127 concentration in the membranes, the surface roughness of the membranes decreased and hydrophilicity and permeation fluxes increased notably. Furthermore, it was observed that the addition of the Pluronic F-127 polymer into the membranes reduced reversible/irreversible membrane fouling. Additionally, a characterisation of the fouled membranes was performed for the purpose of comprehensively understanding the membrane fouling mechanism caused by microalgal culture.     

Novel method for the preparation of ionically crosslinked sulfonated poly(arylene ether sulfone)/polybenzimidazole composite membranes via in situ polymerization

A series of ionically crosslinked composite membranes were prepared from sulfonated poly(arylene ether sulfone) (SPAES) and polybenzimidazole (PBI) via in situ polymerization method. The structure of the pristine polymer and the composite membranes were characterized by FT-IR. The performance of the composite membranes was characterized. The study showed that the introduction of PBI led to the reduction of methanol swelling ratio and the increase of mechanical properties due to the acid–base interaction between the sulfonic acid groups and benzimidazole groups. Moreover, the oxidative stability and thermal stability of the composite membranes were improved greatly. With the increase of PBI content, the methanol permeability coefficient of the composite membranes gradually decreased from 1.59 × 10⁻⁶ cm²/s to 1.28 × 10⁻⁸ cm²/s at 30 °C. Despite the fact that the proton conductivity decreased to some extent as a result of the addition of PBI, the composite membrane with PBI content of 5 wt.% still showed a proton conductivity of 0.201 S/cm at 80 °C which could actually meet the requirement of proton exchange fuel cell application. Furthermore, the composite membranes with PBI content of 2.5–7.5 wt.% showed better selectivity than Nafion117 taking into consideration the methanol swelling ratio and proton conductivity comprehensively.     

Preparation of high-permeance MFI membrane with the modified secondary growth method on the macroporous α-alumina tubular support

MFI membrane with high permeance was successfully synthesized on the macroporous (pore size of 3–4 μm) α-Al₂O₃ tubular support with a novel modified secondary growth method. Before the crystallization, the seeded support was wrapped with Teflon tape in order to focalize the growth of crystals in the region of seed layer. The as-synthesized membrane was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and single-gas permeation testing. The results indicated that the as-synthesized membrane had a thickness of 6–8 μm similar to the thickness of the seed layer and exhibited high gas permeance. At room temperature, the permeance of H₂ and the ideal separation factor of H₂/SF₆ reached 1.64 × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ and 71, respectively. The permeance of single-gas increased with the increasing of temperature. The ideal separation factors of H₂/i-C₄H₁₀ and H₂/SF₆ decreased with the increasing of temperature from 298 to 473 K. At 473 K, the ideal separation factors of H₂/i-C₄H₁₀ and H₂/SF₆ were 12.16 and 11.08, which were still higher than their Knudsen ratios of 5.39 and 8.54, respectively.     

Homogeneous liquid-liquid extraction combined with gas chromatography-electron capture detector for the determination of three pesticide residues in soils

In this study, a new method was developed for analyzing malathion, cypermethrin and lambda-cyhalothrin from soil samples by using homogeneous liquid–liquid extraction (HLLE) and gas chromatography with electron capture detector (GC–ECD). Acetone was used as extraction solvent for the extraction of target pesticides from soil samples. When the extraction process was finished, the target analytes in the extraction solvent were rapidly transferred from the acetone extract to carbon tetrachloride, using HLLE. Under the optimum conditions, linearity was obtained in the range of 0.05–40 μg kg⁻¹ for malathion, 0.04–10 μg kg⁻¹ for lambda-cyhalothrin and 0.05–50 μg kg⁻¹ for cypermethrin, respectively. Coefficients of correlation (r²) ranged from 0.9993 to 0.9998. The repeatability was carried out by spiking soil samples at concentration levels of 2.5 μg kg⁻¹ for lambda-cyhalothrin, and 10 μg kg⁻¹ for malathion and cypermethrin, respectively. The relative standard deviations (RSDs) varied between 2.3 and 9.6% (n = 3). The limits of detection (LODs), based on signal-to-noise ratio (S/N) of 3, varied between 0.01 and 0.04 μg kg⁻¹. The relative recoveries of three pesticides from soil A1, A2 and A3 at spiking levels of 2.5, 5 and 10 μg kg⁻¹ were in the range of 82.20–91.60%, 88.90–110.5% and 77.10–98.50%, respectively. In conclusion, the proposed method can be successfully applied for the determination of target pesticide residues in real soil samples.     

Surface redox polymerized SPEEK–MO2–PANI (M = Si, Zr and Ti) composite polyelectrolyte membranes impervious to methanol

We reported sulfonated poly(ether ether ketone) (SPEEK, 61% degree of sulfonation)–metal oxides (MO₂:SiO₂, TiO₂ and ZrO₂)–polyaniline composite membranes. Metal oxides were incorporated into the swelled SPEEK membrane by sol–gel method and cured by thermal treatment. SPEEK–metal oxide membranes surfaces were modified with polyaniline (PANI) by a redox polymerization process. It was observed that water retention capacity of membrane was increased and methanol permeability was reduced due to synergetic effect of metal oxides and surface modification with polyaniline. These composite membranes showed extremely low methanol permeability (1.9–1.3 × 10⁻⁷ cm² s⁻¹), which was lower than till reported values either for SPEEK–metal oxide or SPEEK/PANI membranes. Relatively high selectivity parameter (SP) values at 343 K of these membranes, especially S–SiO₂–PANI and S–TiO₂–PANI, indicated their great advantages over Nafion117 (N117) membrane for targeting on moderate temperature applications due to the synergetic effect of MO₂ and PANI in SPEEK matrix. S–TiO₂–PANI and N117 showed comparable cell performance in direct methanol fuel cell (DMFC).     

PEG-coated reverse osmosis membranes: Desalination properties and fouling resistance

This study focuses on the use of surface-coated reverse osmosis (RO) membranes to reduce membrane fouling in produced water purification. A series of crosslinked PEG-based hydrogels were synthesized using poly(ethylene glycol) diacrylate as the crosslinker and poly(ethylene glycol) acrylate, 2-hydroxyethyl acrylate, or acrylic acid as comonomers. The hydrogels were highly water permeable, with water permeabilities ranging from 10.0 to 17.8 (L μm)/(m² h bar). The hydrogels were applied to a commercial RO membrane (AG brackish water RO membrane from GE Water and Process Technologies). The water flux of coated membranes and a series-resistance model were used to estimate coating thickness; the coatings were approximately 2 μm thick. NaCl rejection for both uncoated and coated membranes was 99.0% or greater, and coating the membranes appeared to increase salt rejection, in contrast to predictions from the series-resistance model. Zeta potential measurements showed a small reduction in the negative charge of coated membranes relative to uncoated RO membranes. Model oil/water emulsions were used to probe membrane fouling. Emulsions were prepared with either a cationic or an anionic surfactant. Surfactant charge played a significant role in membrane fouling even in the absence of oil. A cationic surfactant, dodecyltrimethyl ammonium bromide (DTAB), caused a strong decline in water flux while an anionic surfactant, sodium dodecyl sulfate (SDS), resulted in little or no flux decline. In the presence of DTAB, the AG RO membrane water flux immediately dropped to 30% of its initial value, but in the presence of SDS, its water flux gradually decreased to 74% of its initial value after 24 h. DTAB-fouled membranes had lower salt rejection than membranes not exposed to DTAB. In contrast, SDS-fouled membranes had higher salt rejection than membranes not exposed to SDS, with rejection values increasing, in some cases, from 99.0 to 99.8% or higher. In both surfactant tests, coated membranes exhibited less flux decline than uncoated AG RO membranes. Additionally, coated membranes experienced little fouling in the presence of an oil/water emulsion prepared from DTAB and n-decane. For example, after 24 h the water flux of the AG RO membrane fell to 26% of its initial value, while the water flux of a PEGDA-coated AG RO membrane was 73% of its initial value.     

Modifying bipolar membranes with palygorskite and FeCl3

To explore a more function-stable and energy-efficient bipolar membrane, palygorskite and FeCl₃ were added at the intermediate layer as water-splitting catalysts. As proven, the two materials have a synergetic effect on water splitting. Particularly, the bipolar membrane modified with 5 g dm⁻³ palygorskite and 0.005 mol dm⁻³ FeCl₃ can achieve a voltage drop of 0.68 V at 100 mA cm⁻² and loses only 14.7 μg of Fe after an electrodialysis operation at 100 mA cm⁻² for 660 min. Obviously, palygorskite can protect ferric ions from significant loss, which makes the membrane stable in the performance of water splitting. Nevertheless, how palygorskite immobilizes ferric ions is still under investigation.     

Voltammetric determination of quercetin at a multi-walled carbon nanotubes paste electrode

Quercetin can effectively accumulate at multi-walled carbon nanotubes-paraffin oil paste electrodes (CNTPE) and cause a sensitive anodic peak at around 0.32 V (vs. SCE) in a 0.10 M phosphate buffer solution (pH = 4.0). Under optimized conditions, the anodic peak current is linear to quercetin concentration in the ranges of 2.0 × 10^− 9−1.0 × 10^− 7 M and 1.0 × 10^− 7−2.0 × 10^− 5 M, and the regression equations are i_p (μA) = 0.0017 + 0.928c (μM, r = 0.999) and i_p (μA) = 0.183 + 0.0731c (μM, r = 0.995), respectively. This paste electrode can be regenerated by repetitively cycling in a blank solution for about 2 min. A 1.0 × 10^− 6 M quercetin solution is measured for 10 times using the same electrode regenerated after every determination, and the relative standard deviation of the peak current is 1.7%. The method has been applied to the determination of quercetin in hydrolysate product of rutin and the recovery is 99.2–102.6%. In comparison with graphite paste electrode, carbon nanotubes-nujol paste electrode and carbon nanotubes casting film modified glassy carbon electrode, the CNTPE gives higher ratio of signal to background current and better defined voltammetric peak.     

Pluronic F-127: An Efficient Delivery Vehicle for 3-(1'-hexyloxy)ethyl-3-devinylpyropheophorbide-a (HPPH or Photochlor)

To determine the impact of delivery vehicles in photosensitizing efficacy of HPPH, a hydrophobic photosensitizer was dissolved in various formulations: 1% Tween 80/5% dextrose, Pluronic P-123 and Pluronic F-127 in 0.5%, 1% and 2% phosphate buffer solutions (PBS). HPPH was also conjugated to Pluronic F-127, and the resulting conjugate (PL-20) was formulated in PBS. Among the different delivery vehicles, only Pluronic P-123 displayed significant vehicle cytotoxicity, whereas Pluronic F127 was nontoxic. Compared to PL-20, HPPH formulated in Tween80 and Pluronic F-127 showed higher cell-uptake, but lower long-term retention in Colon26 cell compared to PL-20. The higher retention of PL-20 was similarly observed during in vivo uptake with BALB/c mice baring Ct26 tumors. In contrast to the in vitro uptake experiments, PL-20 showed slightly higher uptake compared to HPPH formulated in Tween or Pluronic-F127. A significant difference in pharmacokinetic profile was also observed between the HPPH-Pluronic formulation and PL-20. Under similar in vivo treatment parameters (drug dose 0.47 µmol kg⁻¹, light dose: 135 J cm⁻² at 24 h post-injection of PS), HPPH formulated either in Tween or Pluronic F-127 formulation showed similar in vivo PDT efficacy (20–30% tumor cure on day 60), whereas PL-20 showed 40% tumor cure (day 60).     

Preparation of PTFE-based fuel cell membranes by combining latent track formation technology with graft polymerization

Swift heavy 56 MeV ¹⁵N³⁺ ions were generated with particle fluences of 0, 3×10⁶, 3×10⁷, 3×10⁸, 3×10⁹ ions/cm² to form a latent track zone in a 25-μm-thick film of polytetrafluoroethylene (iPTFE). Styrene (St) was then grafted onto the iPTFE films by UV-irradiation or pre-γ-irradiation, and after sulfonation iPTFE-based proton-conducting membranes were obtained, here called, iPTFE-g(UV)-PStSA and iPTFE-g(γ)-PStSA membranes, respectively, which had a straight cylindrical damage zone around the ion path. The degree of grafting was found to be about 7.5% with a particle fluence of 3×10⁷ ions/cm² and with either the UV-method or the γ-method. The ion-exchange capacity, proton conductivity in the thickness direction, MeOH permeability, tensile strength and elongation at break of the obtained iPTFE-g(UV)-PStSA membrane were 0.50 mmol/g, 0.06 S/cm, 0.15×10⁻⁶ cm²/s, 50 MPa and 600%, in contrast to 0.06 mmol/g, 0.06 S/cm, 0.35×10⁻⁶ cm²/s, 19 MPa and 210% for the iPTFE-g(γ)-PStSA membrane, respectively. In comparison, the Nafion 112 measured in our laboratory exhibited an ion-exchange capacity of 0.91 mmol/g, a proton conductivity of 0.06 S/cm, a MeOH permeability of 1.02×10⁻⁶ cm²/s, a tensile strength of 35 MPa and an elongation at break of 295%. It can be concluded from these data that the lower crossover of MeOH, the same proton conductibility, the lower ion-exchange capacity, and the superior mechanical properties of the UV-grafted proton-conducting membranes compared to the Nafion make them promising materials for widespread application in direct methanol fuel cells. On the other hand, the tests of mechanical strength showed that the PTFE base film is subject to degradation by the ion-beam irradiation as well as the γ-irradiation.     

Ceramic asymmetric hollow fibre membranes—One step fabrication process

Ceramic hollow fibre membranes which have an asymmetric structure have been prepared in one step, using an immersion induced phase inversion technique. With this method, membranes with a high surface area per unit volume ratio can be produced, while production cost is dramatically reduced. Yttria-stabilised zirconia (YSZ) is selected as a membrane material, as it is relatively inexpensive and has superior mechanical strength as well as oxygen ion conducting properties. Therefore, both the porous and non-porous membranes prepared from the YSZ have potential applications. For example, the porous YSZ membranes can be used for fluid separations in harsh environments where normal polymeric membranes cannot be sustained, while the non-porous YSZ membranes can be applied as a solid electrolyte in electrochemical devices such as solid oxide fuel cells, oxygen pumps and chemical gas sensors.Gas permeation analysis suggests that non-porous YSZ hollow fibre membranes can be prepared at sintering temperature of 1400 °C or greater, below which the membrane contains pores. Pore sizes of the YSZ porous membrane prepared fall into the pore size range of ultrafiltration membranes. However, the surface porosities of the membranes prepared from two-population sized particles at sintering temperatures of 1200 °C and 1400 °C are around 5000 m⁻¹ and 300 m⁻¹, respectively. The former is comparable to polymeric membranes, while the latter is an order of the magnitude smaller.     

Lipid barrier layers on surfaces of synthetic water permeable membranes

Barrier layers (area 0.79 cm²) from oxidized cholesterol or mixtures of oxidized cholesterol with phosphatidyl serine or phosphatidyl ethanol amine were formed on surfaces of different water-permeable synthetic membranes in 0.1 M NaCl as models of biological membranes. Ionic conductivity across the membranes decreased from 10⁻²-10⁻³ to 10⁻⁷-10⁻⁸ Ω⁻¹ cm⁻² when the barrier layers were formed on their surfaces. Average thicknesses of barrier layers 4.5–11 nm were estimated from electric capacitance. The layers were unstable with lifetimes ranging from several minutes to 50 hr according to the support membrane used. The interfacial tension between synthetic membrane surface and either water or lipid solution was calculated from contact angle measurement. The relation between barrier layer stability and hydrophobic and polar interaction of lipids with support surface was studied. The most stable barrier layers (lifetimes 30–50 hr) were formed on cellophane and gelatin membranes with surfaces hydrophobized by reaction with palmytoyl chloride.