Polymers in contact lens applications VI. The ‘dissolved’ oxygen permeability of hydrogels and the design of materials for use in continuous-wear lenses

The ‘dissolved’ oxygen permeabilities (Pd) of a range of hydrogels have been studied at 25 and 34°C (the temperature of the eye). At both temperatures the equilibrium water content (W) was found to be the major controlling factor in determining oxygen permeability and log (Pd) was found to be linearly related to W. The values of Pd at 34°C were found to be approximately twice those at 25°C throughout the range of water contents studied. Available information on corneal oxygen consumption rates is used as a basis for the prediction of oxygen permeability/thickness requirements in continuous wear lenses. These data lead in turn to predicted minimum equilibrium water contents for hydrogels in this, type of application.     

Permeability of synthetic poly(α-amino acid) membranes to oxygen dissolved in water

Membranes of synthetic poly(α-amino acids), namely, poly(γ-methyl L -glutamate) (PMLG), poly(γ-benzyl L -glutamate) (PBLG), poly(L -glutamic acid) (PLGA), poly(L -methionine) (PLM), and poly(N^?-carbobenzoxy-L -lysine) (PCLL), were prepared and their permeabilities of oxygen dissolved in water were measured in the 8–50°C temperature range using an oxygen electrode. Permeation curves for the poly(α-amino acid) membranes did not approach steady-state currents because of membrane degradation. To eliminate this, the membranes were laminated between polystyrene membranes; thus, the poly(α-amino acid) membranes came in direct contact with neither cathode surface nor electrolyte solution. No effect of membrane thickness on the permeability was observed. The Arrhenius plots of permeability coefficients for PCLL appear to change slope at about 22°C. This is consistent with the diffusion of oxygen in PCLL through the side-chain regions between helices. Comparisons between the permeability of oxygen dissolved in water and permeability of gaseous oxygen obtained by the high-vacuum method and between the activation energy of permeation of dissolved oxygen and that of gaseous oxygen were made in order to elucidate the effect of water on the oxygen permeation of each polymer. The permeability of the poly(α-amino acid) membranes to dissolved oxygen appears to depend on the properties of the side chains of the polymers.     

Synthesis and chemo-physical properties of hydrogels

Hydrogels are synthesized from methyl methacrylate (MMA) and N-vinyl-2-pyrrolidone (NVP) with 1,1,1-trimethylol propane trimethacrylate (TPTA) as a crosslinking agent. It was polymerized under UV radiation (365nm) with a small amount of photosensitizer, diethoxy acetophenone (DEAP), acclerator and diluent, triethanol amine (TEA). The hydrogels were characterized by measuring the water retention, dissolved oxygen diffusivity and permeability, mechanical strength, and light transparency. The hydrogels can retain water up to 80 wt.-% and the mechanical strenght is weakened as the water content is increased in the gel. The dissolved oxygen diffusivity and permeability in the swelling hydrogels are determined to be 10^?6 cm²/sec and 10¹³ cm²s^?1 Pa^?1, respectively. The light transparency is over 90% in the wave lenght ranging from 500 to 700 nm.     

MMA/TPX homograft membrane for oxygen enrichment

Utilizing the factors of degradation and crosslinking of TPX polymer and high O₂/N₂ selectivity of MMA, the performances of MMA homografted TPX membrane are efficiently improved compared to those of pure TPX membrane. The degradation and crosslinking of TPX polymer solution with or without dissolved oxygen during irradiation were observed and proved in existence by the gas permeability, mechanical, and viscosity change study. High O₂/N₂ permeability ratio of 7.6 and fairly high oxygen permeability of 28 × 10^?10 cm³ cm/cm² s cm Hg of the membrane which was cast from the degassing polymer solution, with 20% degree of MMA grafting, can be obtained. Also the membrane for high oxygen permeability of 63 × 10^?10 cm³ cm/cm² s cm Hg with an O₂/N₂ permeability ratio of 4.5, which was cast from the polymer solution with dissolved oxygen, can be obtained under the condition of 60 h irradiation time and about 7% degree of grafting. O₂/N₂ selectivity of TPX membrane can be improved by homografting method with lower MMA grafting degree than that of heterografting method.     

Preparation of vinylpyridine irradiation-grafted poly(4-methyl-pentene-1) membrane for oxygen enrichment

By adjusting the casting conditions, the oxygen permeabilities of poly(4-methyl-pentene-1) (TPX) membranes prepared in this study are in the range of 2.91–7.14 × 10^?9 cm³(STP) cm/cm² s cm Hg and permeability ratio of O₂/N₂ between 2.7 and 4.4. To increase O₂? N₂ selectivity, the vinylpyridine is γ-ray irradiation-grafted onto the substrate–TPX membrane. The factors that affect the structure and performance of the grafted membrane considered are: tightness of substrate, kind of solvent for grafting monomers, irradiation conditions, total irradiation dose, and operating temperature and pressure. The O₂/N₂ selectivities of grafted TPX membranes are significantly improved comparing to that of nongrafted TPX membranes. For example, an O₂ permeability of 35.6 × 10^?10 cm³(STP) cm/cm² s cm Hg and an O₂/N₂ permeability ratio of 7.5 for the grafted membrane can be obtained.     

Preparation and characterization of sulfonated block‐graft copolyimide/sulfonated polybenzimidazole blend membranes for fuel cell application

Polymer electrolyte blend membranes composed of sulfonated block‐graft polyimide (S‐bg‐PI) and sulfonated polybenzimidazole (sPBI) were prepared and characterized. The proton conductivity and oxygen permeability coefficient of the novel blend membrane S‐bg‐PI/sPBI (7 wt%) were 0.38 S cm^?1 at 90 °C and 98% relative humidity and 7.2 × 10^?13 cm³(STP) cm (cm² s cmHg)^?1 at 35 °C and 76 cmHg, respectively, while those of Nafion^® were 0.15 S cm^?1 and 1.1 × 10^?10 cm³(STP) cm (cm² s cmHg)^?1 under the same conditions. The apparent (proton/oxygen transport) selectivity calculated from the proton conductivity and the oxygen permeability coefficient in the S‐bg‐PI/sPBI (7 wt%) membrane was 300 times larger than that determined in the Nafion membrane. Besides, the excellent gas barrier properties based on an acid ? base interaction in the blend membranes are expected to suppress the generation of hydrogen peroxide and reactive oxygen species, which will degrade fuel cells during operation. The excellent proton conductivity and gas barrier properties of the novel membranes promise their application for future fuel cell membranes. © 2015 Society of Chemical Industry     

Chelate membrane from poly(vinyl alcohol)/poly(n-salicylidene allyl amine) blend. II. Effect of co(II) content on oxygen/nitrogen separation

Facilitated transport of oxygen was performed through chelate membranes containing cobalt with selective oxygen binding ability as a fixed oxygen carrier. Chelate membranes were obtained from Schiff base membranes after treating a poly(allyl amine) (PAAm) and poly(vinyl alcohol) (PVA) blend with salicylaldehyde. It is confirmed that the O? O stretching peak through a frequency change in FTIR could be seen at 1150 cm^?1 between cobalt in the membrane and incoming oxygen. The permeability of oxygen through Schiff base membranes was 2.01?2.98 × 10^?13 [cm³ (STP) cm²/cm s cmHg] and oxygen permselectivity was in the range of 1.83?3.27. For chelate membranes, both the permeability of oxygen and oxygen selectivity increased to 2.15?2.82 × 10^?12 [cm³ (STP) cm²/cm s cmHg] and around 8, respectively. Permselectivity of chelate increased as a result of facilitation of O₂ and inhibition of N₂ transport. Detailed results and the mechanism of facilitation of oxygen are discussed on the basis of molecular interactions. © 1995 John Wiley & Sons, Inc.     

Polymers in contact lens applications VII. Oxygen permeability and surface hydrophilicity of poly(4-methylpent-1-ene) and related polymers

Some of the problems and advantages in the use of non-hydrogel polymers in contact lenses are discussed together with studies on a series of such polymers which have potential advantages over the established material, poly(methyl methacrylate), in that they are both more flexible and more oxygen-permeable. Of the polymers examined which are all too hydrophobic for direct use, poly(4-methylpent-l-ene) proved to be the most readily modified in such a way that its surface became sufficiently wettable to sustain a coherent tear film without reducing its optical qualities to an unacceptable level. The ‘dissolved’ and ‘gaseous’ oxygen permeability coefficients of this polymer were studied as a function of film thickness, surface hydrophilicity and temperature. A pronounced boundary layer effect was observed in ‘dissolved’ oxygen permeability studies, although this decreased as the surface was treated to make it more wettable (as indicated by the equilibrium advancing water contact angle). The ‘gaseous’ permeability coefficients of oxygen were found to be some 4-6 times greater than those for nitrogen. A discontinuity corresponding to the glass transition temperature was observed at 28°C with both permeants and apparent activation energies for permeation were determined both above and below this temperature.     

Plasma-modified Nylon 4 membrane for dialysis

The effects of plasma treatment conditions, such as supply power, treatment time, gases used in reactor, surface energy, water content, dialysis permeability, partition coefficient, diffusion coefficient, and free volume of Nylon 4 membranes, were studied. The solutes considered for dialysis system were NaCl, urea, and MgCl₂. The permeabilities of NaCl and urea of membranes with plasma treated in argon at 80 W for 20 min are 5.57 × 10^?5 and 5.89 × 10^?5 cm²/min, respectively. Much higher permeabilities of NaCl and urea obtained by oxygen plasma-treated membranes under 20 W and for 20 min are 30.74 × 10^?5 and 17.66 10^?5 cm²/min, respectively, compared to that of untreated Nylon 4 membranes.     

Enhanced mechanical flexibility and performance of sodium alginate polymer electrolyte bio‐membrane for application in direct methanol fuel cell

A new membrane was synthesized containing pure alginate, crosslinking agent (CaCl₂), and plasticizer (glycerol). Characterization studies of the membrane were applied to determine the characteristics and morphology using field emission scanning electron microscope, EDX, FTIR, XRD, and atomic force microscopy analysis. The half‐cell performance test of the membrane was verified by several tests, including proton conductivity and methanol permeability. The best membrane had high proton conductivity (10.1 × 10^?3 S cm^?1) and very low methanol permeability (1.984 × 10^?7 cm² s^?1), which consequently resulted in very high selectivity (5.0907 × 10⁴ Ss cm^?3). Glycerol had a positive modification and good influence on the alginate characteristics. Furthermore, the poor mechanical properties of the alginate biopolymer were enhanced by calcium chloride and glycerol inside the polymer. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46666.     

Selective ion permeation through fluorocarbon polymer membrane

Hydrophobic polymers have rarely been used for membrane materials, but ions permeated selectively through a very thin hydrophobic membrane under a pressure gradient. The membrane was prepared by coating fluorocarbon polymer on a Teflon membrane filter. The permeabilities of strongly hydrated hydrophilic ions and hydrophobic ions are high through the membrane, but those of weakly hydrated ions are low. The selectivities were enlarged in the mixed salts solution of a low concentration at a high pressure. For example, the permeability of KCl was 0.077 and that of LiCl was 0.80 at 1 × 10^?4 mol/dm³ and 40 kg/cm². The coupling between volume flux and ion flux was high for strongly hydrated ions, while the diffusion flux derived by a concentration gradient was high for weakly hydrated ions.     

Permeabilität galvanisch beschichteter Polymerfolien. I. Methode zur Messung der Gaspermeabilität

The construction and function of an apparatus for the determination of gas permeability through metallized polymer films is described. The test gases N₂, O₂, and CO₂ penetrate under pressure differences from 100 torr to 20 bar through galvanized ABS films (acrylonitrile–butadiene–styrene copolymer). The metallic layers consists of chemically deposited Ni and a galvanic deposited Cu having a thickness of 2–30 μm. The quantity of permeated gases is determined by gas chromatography. The lowest permeability coefficient obtained is 10^?17 (cm³ cm/cm² sec torr). Leak effects can be measured quantitatively. The permeability of gas mixtures (i.e., air) can also be investigated. The apparatus allows the determination of extremely low permeability rates as well as those for conventional polymer systems.     

Preparation of phosphorylated nata‐de‐coco for polymer electrolyte membrane applications

Fuel cells are being developed to overcome the global energy crisis. The objective of this research is to prepare an environmental‐friendly and cheap material as the polymer electrolyte membrane. Coconut water was fermented by Acetobacter xylinum to produce nata‐de‐coco and the phosphorylation was carried out by microwave‐assisted reaction. The resulting membranes are characterized by ion exchange capacity, contact angle, proton conductivity, swelling index, methanol permeability, mechanical properties measurement and morphological analysis. At the optimum phosphorylation condition using 17.35 mmol of phosphoric acid, membrane showed a proton conductivity of 1.2 × 10^?2 S/cm and a methanol permeability of 2.3 × 10^?6 cm²/s. The tensile strength of the produced membranes increases significantly and the arrangement of the cellulosic fibers are kept well‐aligned. It is concluded that a green and sustainable natural resources can be used for preparing electrolyte membrane. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

“Pore/bead” membrane for rechargeable lithium ion batteries

A special “pore/bead” membrane was prepared with a mesoporous inorganic filler (MCM‐41) and a P(VDF‐HFP) binder. The special “pore/bead” structure of the MCM‐41 filler not only enhanced the puncture strength of the membrane but also improved its ionic conductivity. The puncture strength of the dried “pore/bead” membrane (MCM‐41 : P(VDF‐HFP) = 1 : 1.5) was 18 N, and showed a slight decrease (16 N) after the membrane was wetted by liquid electrolyte. Additionally, the composite membrane showed excellent thermal dimensional stability. The composite membrane could be activated by adding 1M LiClO₄‐EC/DMC (1 : 1 by volume). The activated membrane displayed a high ionic conductivity about 3.4 × 10^?3 S cm^?1 at room temperature. Its electrochemical stability window was up to 5.3 V vs. Li/Li⁺, indicating that it was very suitable for lithium‐ion battery application. The battery assembled using the composite electrolyte also showed reasonably good high‐rate performance. The approach of preparing a “pore/bead” membrane provides a new avenue for improving both the conductivity and the mechanical strength of polymer electrolytes for lithium batteries. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

TPX/siloxane blend membrane for oxygen enrichment

The effects of composition, molecular weight, and milling temperature on homogeneity, gas permeability, selectivity of oxygen/nitrogen, and mechanical strength of the TPX/siloxane blend membranes were studied. By adjusting the blending conditions and hence controlling the homogeneity, the gas permeability of TPX membrane was significantly improved without loss of oxygen/nitrogen selectivity. The oxygen permeability of 1.57 × 10^?8 cm³ (STP) cm/cm² s cm Hg and the oxygen/nitrogen permeation ratio of 6.92 can be obtained under the condition of TPX (MX-001)/siloxane (75,000 MW) = 9/1 at 65°C milling temperature. This membrane possesses 133 kg/cm² tensile strength and 92% elongation. The morphology of the blend membranes was studied.     

Suppression of radiation‐induced oxidation of polymers by sputtered silicon oxide coating

Oxygen barrier coating on polymers was attempted to obtain polymeric composite materials with improved radiation resistance. Silicon oxide (SiO_1.6) films ranging from 120 to 240 nm thick were formed on polypropylene (PP) and polyethylene (PE) by radio frequency (RF) magnetron sputtering. Oxygen permeability after SiO_1.6 deposition was reduced significantly in all samples studied, indicating that silicon oxide is a useful gas barrier. The oxygen permeability coefficient of deposited films for PP was 1.7–2.2 × 10^?14 cm³‐cm/cm²/s/cmHg and that for PE was 2.8–4.8 × 10^?13 cm³‐cm/cm²/s/cmHg. We studied the effect of such films on the radiation resistance of polymers in the presence of oxygen by microscopic infrared (IR) absorption spectroscopy. Silicon oxide films 180 nm thick were deposited on the surfaces of PP and PE, and the formation of carbonyl groups after irradiation in air was measured as a function of depth from the surface. Results compared with those for uncoated PE and PP showed that the radiation‐induced polymer oxidation is dramatically suppressed by silicon oxide coating. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 186–190, 2002     

New organic–inorganic hybrid membranes based on sulfonated polyimide/aminopropyltriethoxysilane doping with sulfonated mesoporous silica for direct methanol fuel cells

A series of novel composite methanol‐blocking polymer electrolyte membranes based on sulfonated polyimide (SPI) and aminopropyltriethoxysilane (APTES) doping with sulfonated mesoporous silica (S‐mSiO₂) were prepared by the casting procedure. The microstructure and properties of the resulting hybrid membranes were extensively characterized. The crosslinking networks of amino silica phase together with sulfonated mesoporous silica improved the thermal stability of the hybrid membranes to a certain extent in the second decomposition temperature (250–400°C). The composite membranes doping with sulfonated mesoporous silica (SPI/APTES/S‐mSiO₂) displayed superior comprehensive performance to the SPI and SPI/APTES membranes, in which the homogeneously embedded S‐mSiO₂ provided new pathways for proton conduction, rendered more tortuous pathways as well as greater resistance for methanol crossover. The hybrid membrane with 3 wt % S‐mSiO₂ into SPI/APTES‐4 (SPI/A‐4) exhibited the methanol permeability of 4.68 × 10^?6 cm² s^?1at 25°C and proton conductivity of 0.184 S cm^?1 at 80°C and 100%RH, while SPI/A‐4 membrane had the methanol permeability of 5.16 × 10^?6 cm² s^?1 at 25°C and proton conductivity of 0.172 S cm^?1 at 80°C and 100%RH and Nafion 117 exhibited the values of 8.80 × 10^?6 cm² s^?1 and 0.176 S cm^?1 in the same test conditions, respectively. The hybrid membranes were stable up to about 80°C and demonstrated a higher ratio of proton conductivity to methanol permeability than that of Nafion117. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Evaluation of mixed‐conducting lanthanum‐strontium‐cobaltite ceramic membrane for oxygen separation

In this study, La_0.4Sr_0.6CoO_3‐δ (LSC) oxide was synthesized via an EDTA‐citrate complexing process and its application as a mixed‐conducting ceramic membrane for oxygen separation was systematically investigated. The phase structure of the powder and microstructure of the membrane were characterized by XRD and SEM, respectively. The optimum condition for membrane sintering was developed based on SEM and four‐probe DC electrical conductivity characterizations. The oxygen permeation fluxes at various temperatures and oxygen partial pressure gradients were measured by gas chromatography method. Fundamental equations of oxygen permeation and transport resistance through mixed conducting membrane were developed. The oxygen bulk diffusion coefficient (D_v) and surface exchange coefficient (K_ex) for LSC membrane were derived by model regression. The importance of surface exchange kinetics at each side of the membrane on oxygen permeation flux under different oxygen partial pressure gradients and temperatures were quantitatively distinguished from the oxygen bulk diffusion. The maximum oxygen flux achieved based on 1.6‐mm‐thick La_0.4Sr_0.6CoO_3‐δ membrane was ～4.0 × 10^?7 mol cm^?2 s^?1at 950°C. However, calculation results show theoretical oxygen fluxes as high as 2.98 × 10^?5 mol cm^?2 s^?1 through a 5‐μm‐thick LSC membrane with ideal surface modification when operating at 950°C for air separation. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Proton-conducting membranes from phosphotungstic acid-doped sulfonated polyimide for direct methanol fuel cell applications

A series of novel hybrid proton conducting membranes based on sulfonated naphthalimides and phosphotungstic acid (PTA) were prepared from N-Methyl Pyrrolidone (NMP) solutions. These hybrid organic-inorganic materials, composed of two proton-conducting components, have high ionic conductivities (9.3 × 10^?2 S cm^?1 at 60 °C, 15% PTA), and show good performance in H₂|O₂ polymer electrolyte membrane fuel cells (PEMFC), previously reported by us. Moreover, they have low methanol permeability compared to Nafion^®112. In this paper we describe, for the first time, the behaviour of these hybrid membranes as electrolyte in a direct methanol fuel cell (DMFC). The maximum power densities achieved with PTA doped sulfonated naphthalimide membrane, operating with oxygen and air, were 34.0 and 12.2 mW cm^?2, respectively; about the double and triple higher than those showed by the non-doped membrane at 60 °C.     

UV-curing of simultaneous interpenetrating network silicone hydrogels with hydrophilic surface

Simultaneous interpenetrating polymer network silicone hydrogels have been prepared by UV-initiated free radical/cationic hybrid photopolymerization of a mixture of methacrylate macromonomer polyethylene glycol diacrylate (PEGDA) and vinyl ether terminated polydimethylsiloxane macromonomer (VESi). The consumption of each macromonomer upon UV-irradiation was monitored in situ by real-time infrared spectroscopy. The analysis of transmission electron microscope indicated that the silicone hydrogels exhibited a heterogeneous morphology. The physicochemical properties of the silicone hydrogels, such as water content, ion permeability, oxygen permeability, and contact angle were investigated. The results showed that water content and ion permeability increased with the PEGDA content in the formulation, and the silicone hydrogels exhibited excellent oxygen permeability with the highest D _k of 248?barrer. The results of contact angle measurements indicated that the silicone hydrogels possessed hydrophilic surfaces with the lowest water contact angle of 32°. The study of the protein resistance revealed that the amount of protein adsorbed was significantly reduced with the PEGDA content in the formulation.