Investigation of liquid diffusion into contact lenses using an electron spin resonance technique

In this study, electron spin resonance (ESR) spectroscopy was used for the first time to investigate liquid diffusion into contact lenses. As contact lenses are not paramagnetic substances, they were labeled with nitroxide spin probes to get an ESR spectrum. Thus, it gives a solid spin‐labeled ESR spectrum. The shape and intensity of the ESR signals depend on the environment of these spin probes. The spin probe environment began to change from solid to liquid if liquid were dropped into the system. Consequently the ESR spectra began to change with time, too. By following these changes, three distinct steps were found. Their diffusion coefficients were determined to be 6.38 × 10^?8 cm²/s for the first step (rapid decay region) and 0.37 × 10^?8 cm²/s for the second step (slow decay region), and 2.50 × 10^?8 cm²/s for the third and last step (desorption region). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2942–2946, 2006     

Determination of diffusion coefficient of oxygen into polymers by using electron spin resonance spectroscopy. II. Poly(vinyl acetate)

Electron spin resonance spectroscopy has been used to follow the kinetics of radical decay during postirradiation oxidation of poly(vinyl acetate). The oxygen uptake of γ-irradiated spherical poly(vinyl acetate) has been determined from changes in the intensity of the ESR signal. The diffusion coefficient (D) of oxygen determined by this technique showed an inverse relation with dose. The value of the diffusion coefficient of oxygen obtained in this study, after correcting for dose and size effects is 4.5 × 10^?8 cm²/s, and is in very good agreement with the literature value of D = 5.1 × 10^?8 cm²/s.     

Determination of oxygen diffusion coefficient of poly(methacrylonitrile) II and the calculation of diffusion activation energy

Poly(methacrylonitrile) (PMAN) samples in the shape of a cylinder used in this study were obtained from methacrylonitrile by bulk polymerization. The electron spin resonance (ESR) method has been used to calculate oxygen diffusion coefficient (D) into PMAN samples exposed to high‐energy radiation at different doses in vacuum by observing the ESR radical signal change. In order to calculate the dose‐independent diffusion coefficient (D₀), ln D values were plotted against dose values. The low dose region of this curve was extrapolated to a zero‐dose value, and D₀ was calculated as D₀ = 3.1 × 10⁻⁹ cm²/s. Although D₀ values were in very good agreement with the one obtained for the thin‐film sample of PMAN, the dose dependence of the oxygen diffusion into the cylindrical PMAN samples was observed as being converse of the thin‐film of PMAN,¹ as expected, because of the big difference of the surface/mass values between relatively big cylindrical PMAN samples and thin‐film of PMAN samples. The activation energy (E_a) values of the oxygen diffusion into PMAN were calculated as E_a1 = 27.9 kJ/mol for the 20–60°C temperature range E_a2 = 74.2 kJ/mol for the temperatures above 60°C of the 36 kGy gamma‐irradiated samples. The temperature value of the break point of activation energy was near to the T_g of PMAN.² © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1108–1118, 1999     

Determination of diffusion coefficient of oxygen into polymers by using electron spin resonance spectroscopy. I. Poly(methyl methacrylate)

A simple technique has been proposed for the measurement of the diffusion coefficient of oxygen into polymeric spheres. The technique is based on the scavenging of radicals produced by high energy radiation by oxygen. The diffusion coefficient of oxygen determined for poly(methyl methacrylate) has shown an inverse dependency on the dose received. Diffusion coefficient determined for low doses (D = 3.4 × 10^?8 cm²/s) as well as that determined after extrapolation to zero dose (D₀ = 3.7 × 10^?8 cm²/s) are in excellent agreement with the values reported in the literature.     

Permeability and partition coefficient of aqueous sodium chloride in soft contact lenses

Transport of physiologic saline through soft contact lenses is important to on‐eye behavior. Using a specially designed Stokes‐diaphragm cell, we measure aqueous NaCl permeabilities through commercial soft contact lenses at 35°C. The permeabilities increase exponentially with the water content of the lenses spanning a range from 10⁻⁷ to 10⁻⁵ cm²/s. Equilibrium partition coefficients are obtained by the back‐extraction of lenses initially immersed in 1M aqueous NaCl. Partition coefficients also increase with lens water content but over a smaller range, from 0.1 to 0.7. Because the partition coefficient values are smaller than the water content of the lenses, ideal theory is not followed. Donnan exclusion, bound water, and excluded volume are proposed explanations. The diffusion coefficients of aqueous NaCl through soft contact lenses increase with increasing lens water content following free‐volume theory. Aqueous NaCl diffusivities in the lower water‐content lenses are smaller than the diffusion coefficient of NaCl in water by factors up to 100 indicating very tortuous diffusion paths. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Optical application of poly(HEMA-<Emphasis Type="Italic">co</Emphasis>-MMA) containing silver nanoparticles and N,N-dimethylacrylamide

High functional ophthalmic lens materials, poly(HEMA-co-MMA)s, were prepared by the copolymerization of HEMA, MMA, NVP, EDGMA, and N,N-dimethylacrylamide in the presence of silver nanoparticles. Silver nanoparticles have antimicrobial properties and a hydrophilic monomer N,N-dimethylacrylamide has excellent biocompatibility and oxygen transmissibility. The water content was in the range of 36.63–44.45%, indicating the characteristics of general water-content contact lenses, and the refractive index was measured to be in the range of 1.423–1.435. Meanwhile, the oxygen transmissibility ranged from 10.63×10⁻¹¹ to 18.85×10⁻¹¹ (cm²/sec)(mlO₂/ml×mmHg) increasing with increasing the addition ratio of N,N-dimethylacrylamide. The polymeric materials satisfied the basic characteristics required for ophthalmic contact lenses. The polymers can be used to fabricate antimicrobial hydrogel contact lenses with high oxygen transmissibility.     

Saccharide radicals induced by UV irradiation at room temperature

The stability of saccharide radicals induced by UV irradiation at room temperature and the ability to initiate polymerization of acrylamide were investigated. UV light of 220 < λ < 300 nm was proved to form saccharide radicals effectively at room temperature. ESR signal intensity of the irradiated saccharide was in the order of sucrose > methyl-α-D-glucopyranoside ? cellobiose > D-xylose > D-glucose α D-fructose. The saccharide radicals were fairly stable at room temperature, however, the markedly declined in amount as the samples were brought to their own melting points or allowed contact with water. When an aqueous solution of acrylamide was added to the irradiated saccharide, polymerization was initiated and the conversion increased with an increasing amount of the preirradiated saccharide. Regarding the kind of saccharide, the conversion decreased in the following order: sucrose > methyl-α-D-glucopyranoside > cellobiose > D-glucose, which indicated a good agreement with the magnitude of ESR signal intensity.     

Analysis of intraparticle diffusion on adsorption of crystal violet on bentonite

Abstract

In the present work, kinetics of crystal violet (CV) adsorption on bentonite was studied by pore volume and surface diffusion model (PVSDM), surface diffusion model (SDM), and pore volume diffusion model (PVDM). The adsorption decay curves were obtained in batch system using different adsorbent dosages. The PVDM model did not interpreted the kinetic adsorption since the calculated value of D_p equal to 5.64?×?10^?7 cm² s^?1 predicted a slower adsorption than that obtained by the experimental data. The PVSDM results indicates that the intraparticle diffusion is predominantly due to surface diffusion (93%) and the pore volume diffusion can be negligible. Once the surface diffusion was the limiting step, the estimation with one (D_s) and two (D_sq and α) parameters were tested in the SDM model. The statistical analysis revealed that the one-parameter SDM model was most appropriate to predict the CV adsorption on bentonite. The optimal values of Ds ranged from 6.19?×?10^?10 to 6.49?×?10^?10 cm² s^?1, and decrease with the adsorbent dosage.     

The effect of photodegradation of polystyrene on its permeability characteristics

The diffusion (D) and permeability (P) coefficients for ¹⁴CO₂ in polystyrene films which had been irradiated by short-wave ultraviolet (253.7 nm) radiation under vacuum and in oxygen were determined in the temperature range of 20° to 55°C. Both D and P decreased with increasing exposure, the vacuum-irradiated sample showing significantly greater decreases, presumably on account of a larger extent of crosslinking which was possible in the absence of oxidation. A good correlation was observed between crosslinking and decreasing P and D values. The solubility coefficients for all irradiated samples increase with increasing dose. Activation energies for diffusion increase with increasing irradiation, particularly for the vacuum-irradiated samples. Reductions in P and D values are interpreted in terms of free-volume decreases due to crosslinking and other modifications, while the increasing activation energies are attributed to the increasing energy requirements for creation of free volume in modified polymers.     

Cellulose graft copolymers. II. Graft copolymerization of ethyl acrylate with γ-irradiated cellulose from acetone–water systems

Ethyl acrylate was graft-copolymerized from acetone–water systems with γ-irradiated, purified cotton cellulose. The scavenging of the free radicals in the irradiated cellulose by water, acetone, and water–acetone systems was determined by electron spin resonance spectroscopy. The ESR spectra of free radicals, scavenged by water and acetone, were recorded by the use of a time-averaging computer attached to the ESR spectrometer, in which the ESR spectrum of the irradiated cellulose, which had been immersed in water and/or acetone, was electronically subtracted from the ESR spectrum of the irradiated cellulose control. For both water and acetone, the ESR spectra of the scavenged free radicals were singlets. This indicated that free radical sites formed on carbon C₁ or C₄ on radiation-initiated depolymerization, which would generate singlet ESR spectra, were readily accessible to these solvents. The maximum scavenging of the radicals was observed when irradiated cellulose was immersed in acetone–water solution which had a composition of 25/75 vol-%. The scavenging of the free radicals in irradiated cellulose when immersed in acetone–water solutions was less than when immersed in methanol–water solutions. Also, the extent of graft copolymerization of ethyl acrylate from acetone solutions with irradiated cellulose was less than that of ethyl acrylate from methanol solutions. These differences were probably due to differences in the diffusion rates of acetone and methanol into the cellulosie structure. The Trommsdorff-type effect in the acetone solutions would be less than in the methanol solutions, since acetone is a better solvent for poly(ethyl acrylate) than methanol.     

Fluorescence measurements of the diffusion coefficient for butylated hydroxyanisole in low-density polyethylene

Measurement of the diffusion coefficient (D) of butylated hydroxyanisole (BHA) in low density polyethylene at 31°C was made by two techniques. (1) Measurement of diffusion rate in the absence of solvent was made by use of a film stack with BHA-loaded discs on top and bottom. After a given diffusion time, the films were separated and the BHA extracted from the films into 1 -propanol. The fluorescence of the solutions provided values of BHA concentration as a function of film position in the stack, from which the value 3.4 (SD 0.3) × 10^?9 cm² s^?1 for D was calculated. (2) Fluorescence monitoring, under oxygen free conditions, was used to measure rate of BHA extraction from a film into 1 -propanol at 31°C, and gave the value 3.8 × 10^?9 cm² s^?1 for D which agrees well with the value determined by measurement in the absence of solvent.     

Permeability of oxygen through polymers. II. The effect of humidity and film thickness on the permeation and diffusion coefficients

The values of the permeability coefficient P (cm²/sec) and the diffusion coefficient D (cm²/sec), of oxygen in some water-soluble polymers at various values of relative humidity were determined. The amount of oxygen initially present in the polymer membranes was calculated. The effect of sample preparation and the film thickness on the transport parameters was investigated. The results confirm the possible effect of thickness on the rate of transport of oxygen in water-soluble polymers.     

Acetone absorption in UV‐irradiated polycarbonate

Isothermal acetone absorption in UV‐irradiated polycarbonate (PC) was investigated at temperatures from ?23 to +25°C. The crystalline fraction of PC increased with UV dose. The anomalous transport data were analyzed based on Harmon's model which includes contributions from Case I transport characterized by the diffusion coefficient, D, and Case II transport characterized the velocity, v. Diffusion coefficients were monitored by both mass uptake using the model (D and v), and movement of the sharp front (D_f). Plots of log of D, v, and equilibrium swelling ratio (ESR) versus 1/T exhibited similar features. That is, plots were linear and superimposable for all doses at the higher temperatures, and exhibited a transition temperature and then a linear region that varied with dose. The values of D, D_f, and v increased with increasing dose, whereas the ESR decreased with dose. The direction of Case II transport was opposite to that of Case I diffusion during which time, sorbed solvent was expelled from the samples. Results are discussed in terms of a solvent‐induced change in lattice structure at the lower temperatures and in terms of UV radiation effects on the PC matrix that enhance solvent crystallization. POLYM. ENG. SCI., 58:1174–1183, 2018. © 2017 Society of Plastics Engineers     

Adhesion of Pseudomonas aeruginosa to contact lenses after exposure to multi-purpose lens care solutions

Elemental surface compositions of contact lenses were measured after exposure to different lens care solutions (LCS) using X-ray photoelectron spectroscopy and were related to adhesion and detachment of Pseudomonas aeruginosa. Etafilcon A and polymacon contact lenses, prior to and after exposure to LCS were fixed on the bottom plate of a parallel plate flow chamber after which P.aeruginosa #3 was allowed to adhere for 2 h. After adhesion, bacterial detachment was stimulated by perfusing the chamber with an LCS or by passing an air-bubble through the chamber. After exposure to an LCS, the adhesion of P.aeruginosa #3 could either be enhanced or decreased, depending on the contact lens and LCS involved. Initial deposition rates of P.aeruginosa #3 could not be related with changes in elemental surface composition of the contact lenses, but decreased with an increasing ratio of oxygen involved in O C bonds relative to oxygen in O C bonds. P.aeruginosa #3 adhered tenaciously to both types of contact lenses and the passage of an air-bubble through the flow chamber detached only up to 9% of the adhering bacteria. Alternatively, the LCS most effective in decreasing bacterial adhesion after exposure (LCS A), was least effective in detaching adhering P.aeruginosa #3 (8-15%), while the other LCS detached up to 42% of adhering bacteria. In conclusion, different LCS have different abilities to detach the adhering P.aeruginosa #3 from contact lens surfaces and all leave adsorbed components on the surface after soaking. Adsorbed components rich in O C bonds increased adhesion of P.aeruginosa #3 under the conditions used in this study and should, therefore, be avoided.     

Spatially resolved indiffusion behavior of Cu2+ and Ni2+ in polypropylene

Microplastics and their effects on the environment and food chain have become increasingly important in recent years. These polymer particles, which are only few millimeters in size or smaller, accumulate in the environment and can enter the human food chain via animals that ingest them. Moreover, they can accumulate impurities such as heavy metals. Therefore, this study focuses on the indiffusion behavior of metal ions into semicrystalline polypropylene (PP) applying time-of-flight secondary ion mass spectrometry (ToF-SIMS) at cryo-conditions. Diffusion coefficients of Cu²⁺ and Ni²⁺ in PP are determined by classical SIMS depth profiling in frozen state (T <−130°C) and subsequent data analysis according to Fick's second law of diffusion. The results show that diffusion of Cu²⁺ ions in dry PP (D_PP,Cu = [2.21 ± 0.15]·10⁻¹² cm²/s) is faster compared to Ni²⁺ ion diffusion of dry PP (D_PP,Ni = [4.43 ± 0.55]·10⁻¹³ cm²/s). Interestingly, the diffusion of Cu²⁺ ions in water-saturated PP (D_PP,H2O,Cu = [1.91 ± 0.28]·10⁻¹³ cm²/s) is slower compared to Cu²⁺ ion diffusion in dry PP. Furthermore, high-lateral resolution ToF-SIMS analysis shows that metal ions only diffuse in certain areas of PP, which are most likely amorphous.     

Behaviour of composites used in the confinement of nuclear wastes. 3. Diffusion of ions through epoxide networks

The diffusion of cesium and chloride ions through epoxide membranes was studied under a variety of conditions including self-diffusion, the presence of other salts in the aqueous solution, an excess of either reagent used in the manufacture of the membrane, the addition of various fillers in the epoxide network and two temperatures. At 23°C, the diffusion coefficient D was (2–6) × 10-¹³cm²s^?1 for most systems, except when the epoxide was prepared with an excess of the dioxirane component or when untreated glass beads were added to the network. In the latter instance D increased and most notably with glass beads. On the contrary, addition of sand to the epoxide resulted in a more effective barrier against diffusion as shown by a decrease in D. It is concluded that most of these materials should be suitable for the confinement of low and medium activity nuclear wastes.     

Structural analysis of electron beam irradiated ethylene-vinyl acetate copolymer (EVA) film (II)

The crosslinked structure of irradiated ethylene-vinyl acetate copolymer (EVA) film was examined by means of ESR, IR and pyrolysis-gas chromatography. The ESR spectrum of 35 Mrad irradiated EVA film with 95g kg^?1 vinyl acetate content consisted of a three-line component with an intensity ratio of 1:2:1, a hyperfine structure coupling of 22.4 G and g factor of 2.0049. Therefore, the spectrum was assigned to the methylene radical with two α protons on the same plane; this radical is formed by loss of a hydrogen atom from the acetoxymethyl group. In pyrolysing EVA films at 500°C, the yield of acetic acid from 10 Mrad-150 g kg^?1 film significantly decreased compared with that of unirradiated film, and it decreased with increasing crosslinking density. By measuring the IR spectra of methanolysed EVA films, the following results were obtained: the absorbances at 1740, 1250 and 1050cm^?1, attributed to the C?O, O?C? O? R and C? O? C groups, respectively, had a marked decrease, whereas the three peaks for 20Mrad film were much stronger than those of unirradiated film. On the basis of these findings, it is suggested that the crosslinking reaction in electron beam irradiated EVA film with lower doses takes place between the acetoxy groups and the main chains.     

Oxygen transport in crosslinked,silicon-containing copolymers of methyl methacrylate

Copolymers of methyl methacrylate and 1,3-bis(methacryloxy methyl)-1,1,3,3-tetramethyl disiloxane were prepared by chemically induced copolymerization/crosslinking at 60°C and 49 mm Hg. Crosslinked, glassy copolymers were obtained with copolymer mole fraction of the silicon-containing monomer varying from 0.09 to 0.55. Oxygen transport studies were performed with thin films as prepared and after sub-T_g annealing. The results of this study indicated that an enhancement of both the steady state oxygen permeation rate and the oxygen diffusion coefficient was achieved through copolymerization. The oxygen diffusion coefficients through the copolymers were found, within experimental error, to be independent of silicon content and ranged from 0.80 × 10^?7 to 1.90 × 10^?7 cm²/s vs. oxygen diffusion coefficient for pure poly(methyl methacrylate) of 1.5 × 10^?8 cm²/s. Sub-T_g annealing effected a reduction of approximately equal magnitude in both the oxygen diffusion coefficient and the steady state oxygen flux for the copolymers. In addition, the normalized oxygen flux data were predicted with Fick's law, assuming constant boundry conditions and diffusion coefficient. These results were explained in terms of the free volume theory and the combined effects of increased crosslinking density, chain mobility, and oxygen solubility with increased copolymer silicon content.     

Fast transient fluorescence technique (FTRT) for studying dissolution of polymer glasses

The fast transient fluorescence technique (FTRT) was used for studying the swelling and dissolution of a glassy polymer formed by free‐radical polymerization of methyl methacrylate (MMA). Anthracene (An) was introduced during polymerization as a fluorescence probe to monitor swelling and dissolution. Swelling and dissolution processes of disc‐shaped poly(methyl methacrylate) (PMMA) glasses in a chloroform–heptane mixture were monitored by measuring the fluorescence lifetimes of An from its decay traces. A method is developed for low quenching efficiencies for measuring lifetimes, τ, of An, and it was observed that τ values decreased as the dissolution process proceeded. Desorption, D, and mutual diffusion, D_m, coefficients of An molecules were measured during dissolution of PMMA and found to be around 5.4 × 10⁻⁶ (cm²/s) and 2.2 × 10⁻⁵ (cm²/s), respectively. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 948–957, 1999