Microporous Glass Research Articles

Optical and lasing characteristics of microporous quartz glass impregnated with a dye-activated epoxy polymer

A new solid-state active medium in the form of microporous quartz glass dye-doped by a coloured epoxy polymer was developed for dye lasers. The specific nature of the structure of this medium ensured improved mechano-physical and thermooptical characteristics combining the good optophysical properties of glasses with a long service life of dye-activated polymers. The rate of change of the refractive index with temperature, dn/dT = -7.5×10-6 K-1, was considerably less than that for the polymers used at present and also less than that for many optical glasses and crystals. Excitation, with YAG : Nd3+ laser radiation in a nonselective resonator, of this glass impregnated with an epoxy polymer activated with rhodamine C gave rise to stimulated emission in the spectral range 610-640 nm, and the efficiency of such emission was ~20%. In a distributed-feedback laser the tuning range was 607-665 nm and the width of the spectral line was 0.03 nm. The service life was ~104 shots, which matched the best dye-doped solid-state matrices under these conditions.

Protein fractionation using fast flow immobilized metal chelate affinity membranes

A new group-specific affinity membrane using metal chelates as ligands and inorganic glass hollow fiber microfiltration membranes as support matrices is developed and tested. The study focused on developing the optimum activation and coupling procedures to bind the chelating agent (iminodiacetic acid, IDA) to the surface of the microporous glass hollow fiber membrane and testing the resultant affinity membrane. Starting with three different glass surfaces, five modification reactions were evaluated. All the modified "active surfaces" were first tested for their protein adsorptive properties in batch mode with suspended microporous glass grains using model proteins with known binding characteristics with Cu-IDA systems. The metal loading capacities of the surfaces exhibiting favorable fractionation were then measured by atomic absorption spectroscopy.The results were compared with the results obtained with a commercial material used in immobilized metal affinity column chromatography. The protein binding characteristics of the hollow fiber affinity membranes were also evaluated under conditions of convective flow. This was performed by flowing single solute protein solutions through the microporous membrane at different flow rates. These results were then used to estimate the optimum loading and elution times for the process. A mathematical model incorporating radial diffusion was solved using a finite difference discretization method. Comparison between model predictions and experimental results was performed for four different proteins at one flow rate. These results suggested that the kinetics of adsorption was concentration dependent. Finally, the hollow fiber affinity membranes were challenged with two component mixtures to test their ability to fractionate mixed protein solutions. Efficient separation and good purity were obtained.The results presented here represent the development of a new fast flow affinity membrane process-immobilized metal affinity membranes (IMAM). (c) 1994 John Wiley & Sons, Inc.

Synthesis of polymeric microspheres employing SPG emulsification technique

AbstractRelatively uniform polymeric microspheres, the coefficients of variation being close to 10%, were obtained by the BPO‐initiated suspension polymerization of styrenic monomers. Unlike the conventional stirred‐tank system, a particular microporous glass membrane (SPG) provided uniform monomer droplets continuously when monomer was allowed to permeate through the micropores. The monomer droplets were suspended in an aqueous solution containing the stabilizing agents, transferred to a stirred vessel, and polymerized. Up to 10μm spheres, of a far narrower size distribution than those obtained by conventional microsuspension polymerization spheres, were obtained. The initial droplet size and distribution were retained with the successful suppression of secondary particle nucleation by the addition of hydroquinone in the aueous phase. Crosslinked polystyrene spheres were also synthesized in the presence of various low‐molecular‐weight diluents. While a good solvent, toluene, was not so effective; poor solvents, n‐heptane and n‐heptane, easily yielded the microporous structure, the specific surface area being as high as 160 m2/g. © 1994 John Wiley & Sons, Inc.

Preparation of polyamide microcapsules having narrow size distributions.

A novel emulsification technique which employs microporous glass membranes was adopted to prepare polyamide microcapsules of narrow size distribution. This technique proved to be simple and quite efficient for getting fairly uniform sizes of dispersed liquid droplets. Polyamide microcapsules prepared by using this technique were found not completely monodisperse, but far more satisfactory than those by any conventional mechanical methods in view of their narrow size distribution. This method also seems promising to get various sizes of the capsules by selecting the pore size of the glass membranes.

Fibre optic chemical sensors based on evanescent wave interactions in sol-gel-derived porous coatings

A simple, low-cost technique for fabricating reagent-mediated fibre-optic chemical sensors (optrodes) is described and the performance of a range of such sensors is reported. The technique is based on coating an unclad portion of an optical fibre with a microporous glass film prepared by the sol-gel process. Although tip- and side-coating are both possible with this technique, the latter, which employs evanescent wave interactions, offers particular advantages in terms of sensor performance, control of sensitivity and quality of coating. The sol-gel-derived film is used to provide a robust support matrix in which analyte-sensitive dyes are entrapped and into which smaller analyte molecules may diffuse. The benefits of this sol-gel approach to sensor fabrication are illustrated by results from a range of sensors for pH, ammonia and oxygen based on both evanescent wave absorption and evanescent wave excitation of fluorescence.

Adsorption, diffusion and permeation of gases in microporous membranes. III. Application of percolation theory to interpretation of porosity, tortuosity, and surface area in microporous glass membranes

The dependencies of porosity, surface area, and a tortuosity factor in microporous membranes on the porous membrane structure were considered. it was shown that the porosity and tortuosity in silica glasses could be described within the framework of the percolation theory. Tortuosity factors were influenced not only by the elongation of the diffusion path but also by the amount of throughout porosity. Mathematical medoling of gas diffusion processes in microporous glasses was performed by the MonteCarlo method. The simulation results were in good agreement with experimental observations for Vycor glass membranes. Dependence of the surface area per unit volume, S V, on pore size was represented by a simple power law of the type S V∼ f (θ) d −1 P with O < f(θ) < 1.23, where d P is the pore diameter. Experimental data from literature on surface area and porosity in porous carbons, alumina, silica, glasses, silver, nickel, and polymeric membranes were used to verify the relationship. As a first approximation, the surface area per unit volume in porous materials with porosity 0.4 < θ < 0.6 can be estimated as S V ≈ 1.23/ d P.

The separation of gaseous mixtures with composite micropore glass membranes at high temperature

Abstract Separation of gaseous mixtures was carried out up to 773 K using composite microporous glass membranes coated on the surface of porous ceramic tubing. The composition of the metal alkoxide solution used in the coating process was Si(OC 2 H 5 ) 4 :27.9; C 2 H 5 OH:42.0; H 2 O:26.2; HCl:0.3 and H 3 BO 3 :3.6wt%. With the ceramic tubing supplied by TOTO Co., Ltd, much thinner microporous glass membranes can be made, because five coating cycles were enough to obtain a coating free of cracks, compared with at least seven cycles for TDK Co., Ltd material. The membrane can permeate only H 2 O from the thermochemical reaction gas mixture of H 2 and H 2 O, at the flux rate of 37 kg (m 2 day) −1 at a trans-membrane pressure of 0.196 MPa and at 773 K.

血液成分の膜による分離

Techniques of membrane plasma separation consist of microfiltration that is a pressure-driven membrane process for separation of plasma from blood in therapeutic and donor apheresis. Filtration characteristics in plasma separation cannot be explained by the well-known ultrafiltration theory. Elucidation of filtration characteristics and mechanism of fouling is required to develop a highly efficient filter for plasma separation.In this review, filtration characteristics of a small-sized rotating filter for plasma separation composed of flat polycarbonate and Nylon membranes and a plasma filter composed of microporous glass (MPG) membranes were elucidated. The rotating filter was capable of producing higher wall shear rates caused by the formation of Taylo vortices without significant increases in blood-side pressure drop. The MPG membranes are resistant to chemicals, heating and wear, and these membranes have the advantages of the absence of hemolysis and excellent filtration characteristics because of their limited distribution of pore diameter.

Fibre optic oxygen sensor based on fluorescence quenching of evanescent-wave excited ruthenium complexes in sol–gel derived porous coatings

A simple, low-cost technique for the fabrication of optical sensors for oxygen is described and preliminary results obtained using these sensors are reported. The technique is based on coating a declad portion of an optical fibre with a microporous glass film prepared by the sol–gel process. A ruthenium complex [RuII–tris-(2,2′-bipyridine) or RuII–tris(4,7-diphenyl-1,10-phenanthroline)] is trapped in the nanometre-scale cage-like structure of the porous film. In this sensor configuration the complex is excited by the evanescent field of the 488 nm radiation guided by the optical fibre. The luminescence from such complexes is known to be quenched by oxygen and the sensors exhibit repeatable quenching behaviour when exposed to various concentrations of oxygen. The ratio R=I0/I100 where I0 and I100 represent the detected signals from a sensor exposed to 100% nitrogen and 100% oxygen, respectively, is used as a measure of the sensitivity of the sensor. Sensors based on the diphenylphenanthroline complex exhibit greater sensitivity than those based on the bipyridine complex, in accordance with theoretical predictions. More importantly, however, the design potential of the sol–gel process for sensor fabrication is demonstrated by the achievement of a substantial increase in R when the process parameters are adjusted to increase the pore volume.

Adsorption, permeation, and diffusion of gases in microporous membranes. II. Permeation of gases in microporous glass membranes

The gas permeability properties of He, H 2, CO 2 O 2, N 2 and CH 4 in microporous silica membranes were studied as a function of temperature and pressure. A mathetical model of compressible flow in a hollow fiber tube with permeable walls was developed and solved to describe gas transfer in the membranes. The permeation rate of He in the microporous membrane was comparable to that in industrially produced polymeric membranes. Selectivity factors in the membrane were found to be a function of differences in the gas kinetic diameters. The ideal selectivity factor for He/CH 4 was more than 10,000 at 30°C. Selectivity factors decreased with increasing temperature.

Adsorption, permeation, and diffusion of gases in microporous membranes. I. Adsorption of gases on microporous glass membranes

Adsorption of CO 2, H 2O, C 2H 4, CH 4, N 2, C 2H 5OH, and CH 2Cl 2 in microporous silica hollow fiber membranes was studied at temperatures of 30°C and 70°C and at pressures up to 1.3 MPa. The experimental date were fitted with Langmuir, Dubinin-Radushkevic, and Freundlich isotherms. The best fitting model was found to be the Dubinin-Radushkevich isotherm. Based on the fitting results the total under investigation. No capillary condensation of the water and ethanol vapors was observed in the microporous fibers. The limits for the pore diameter, d, of the membrane deduced from the study were 5 < d < 20 Å.

Viscous flow and diffusion of liquids in microporous glasses.

The permeability for viscous flow of microporous materials is proportional to an effective pore cross-sectional area ${\mathit{d}}_{\mathit{t}}^{2}$ and inversely proportional to the tortuosity \ensuremath{\tau}. The tortuosity of microporous Vycor glass was determined from measurements of the self-diffusion coefficients D of hexane and decane using small angle neutron scattering. From the relation for the tortuosity \ensuremath{\tau}=${\mathit{D}}_{\mathit{b}}$/D, where ${\mathit{D}}_{\mathit{b}}$ is the bulk liquid self-diffusion coefficient, we derived values of \ensuremath{\tau} in the range of 3.4--4.2. Using measured values of the permeability of organic liquids in Vycor and the value of \ensuremath{\tau}, we determined ${\mathit{d}}_{\mathit{t}}$=31 \AA{}. This value of ${\mathit{d}}_{\mathit{t}}$ is close to the pore radius obtained from desorption isotherms as well as to the value obtained from the Kozeny-Carman relation.

Membrane Emulsification by Microporous Glass

Membrane Emulsification by Microporous Glass

New Applications for Microporous Glass

New Applications for Microporous Glass

Relaxation and dynamical properties of water in partially filled porous materials using NMR techniques

The study of relaxation times of NMR active nuclei in liquids confined to pore structures allows characterization of the geometry of the open volume providing information regarding its homogeneity, spatial distribution, and tortuosity. Experiments performed on samples containing different amounts of fluid can probe the degree of homogeneity at smaller and smaller length scales, permitting a determination of the intrinsic nature of the liquid-solid interaction responsible for the observed enhancement of the relaxation rates. The results of longitudinal and transverse relaxation experiments on water filling a microporous leached borosilicate glass are discussed. Particular emphasis is devoted to relaxation and dynamical properties at sub-monolayer coverage. This is discussed in the context of the molecular interaction at the liquid-solid interface. The results are interpreted in terms of anisotropic rotation of the adsorbed molecules and the characteristic times of such motion are extracted. This is compared with the molecular translation degree of freedom derived from NMR pulsed field gradient techniques suggesting that the two types of motion are closely related.

Effects of hematocrit on filtrate flux of microporous glass membranes for bovine blood.

Effects of hematocrit on filtrate flux of microporous glass membranes for bovine blood.

ピストンを用いた容積型気体分離膜性能試験装置の試作

In the research and development of gas separation membranes, it is very important to measure the gas permeabilities of membranes readily and precisely.In this report, the new type apparatus based on the volumetric method with piston-feeder was developed for the simple, rapid and precise measurement. With this apparatus, the gas permeabilities were measured for microporous glass, silicone rubber, cellulose acetate membrane and polyester film, and the values obtained were in good agreement with ones obtained by the high-vacuum type apparatus. The experiment of the oxygen enrichment as carried out with air through silicone rubber, and observed values were in fair agreement with calculated ones.

The separation of gaseous mixture with composite microporous glass membranes at high temperature.

Separation of gaseous mixture was carried out in the temperature range from 298 to 773 K using a composite microporous alumina membrane, thin alumina membrane have been prepared on the surface of a porous ceramic tubing by coating wet sol-gel method.Structure of the membranes was investigated by Scanning Electron Microscope, and the best composition of the metal alkoxide solution used in the coating process was Al (OC3H7) 3 : 1, H2O : 100, i-C3H7OH : 0.67 and HCl : 0.07, in molar ratio.The membrane allows to permeate only H2O from thermochemical reaction gas mixture of H2 and H2O at the flux rate of 69kg/ (m2·day) at trans-membrane pressure 98kPa and at 773 K.Taking into account the change of viscosity in the flow direction, the observed data were analysed by the permeation equations proposed by Present and de Bethune, and the calculated results were in good agreement with the observed data.

Dielectric Properties of Microporous Glass in the Microwave Region

The dielectric properties of a high‐silica microporous glass were determined at 5.5 and 11.4 GHz. Two measurement methods were used to measure these properties, the resonant cavity and resonant post (Hakki–Coleman) techniques. The accuracy of the two measurement techniques was evaluated and the limiting conditions of measurement were determined. The glass, consisting of pore sizes on the order of tens of angstroms, was subjected to thermal treatments in an oxidizing atmosphere at temperatures from 300° to 1100°C, and chemical treatments in 2% and 10% HF for varying amounts of time. Heat treatment of the glass at 800°C produced a minimum dielectric constant of 2.8 and loss of 0.001. The acid treatment had little effect on the dielectric properties.

Effect of a magnetic field on the kinetics of the geminal recombination of triplet radical pairs adsorbed on glass with small pores

A kinetic study was carried out for the geminal recombination of triplet radical pairs adsorbed in glass with small pores. The application of an external magnetic field is accompanied by a significant decrease in the fraction of radicals, which recombine in the cage. The magnetic effects in microporous glass are comparable in magnitude with the analogous phenomena in micelles.