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Pure, amine-derivatized and nickel-doped sol–gel silica membranes have been developed on tubular Membralox-type commercial ceramic supports for the purpose of carbon dioxide separation from nitrogen under coal-fired power plant flue gas conditions. An extensive synthetic and permeation test study was carried out in order to optimize membrane CO2 permeance, CO2:N2 separation factor and resistance against densification. Pure silica membranes prepared under optimized conditions exhibited an attractive combination of CO2 permeance of 2.0 MPU (1 MPU = 1 cm3(STP) cm−2 min−1 atm−1) and CO2:N2 separation factor of 80 with a dry 10:90 (v/v) CO2:N2 feed at 25 °C. However, these membranes exhibited flux decline phenomena under prolonged exposure to humidified feeds, especially in the presence of trace SO2 gas in the feed. Doping the membranes with nickel (II) nitrate salt was effective in retarding densification, as manifested by combined higher permeance and higher separation factor of the doped membrane compared to the pure (undoped) silica membrane after 168 h exposure to simulated flue gas conditions.

We present a new processing scheme for the deposition of microporous, sol–gel derived silica membranes on inexpensive, commercially available anodic alumina (Anodisk TM ) supports. In a first step, a surfactant-templated mesoporous silica sublayer (pore size 2–6 nm) is deposited on the Anodisk support by dip-coating, in order to provide a smooth transition from the pore size of the support (20 or 100 nm) to that of the membrane (3–4 u

A new aminosilicate, sol‐gel derived microporous inorganic membrane has been developed for enhanced CO 2 separation in applications such as removal of metabolic CO2 from the breathing loop of the NASA extravehicular mobility unit (EMU), natural gas purification, or CO2 capture from coal-fired power plant emissions. This membrane consists of an inorganic, amorphous silica matrix of pore size 4‐5 ˚ A, containing randomly dispersed amine ( NH2) functional groups in order to enhance its CO2 selectivity, due to preferential adsorption of CO2 in the membrane pore walls and simultaneous blocking of permeation of other gases (O2 ,N 2 and CH4). It is found that the gas feed condition during permeation (partial pressure of CO2, relative humidity), post-synthetic treatments and aging, affect significantly the separation performance of the membranes. At this stage of development, with feeds of 1‐20 vol.% CO 2 and 0‐40% relative humidity at 22 ◦ C, the highest CO2:N2 separation factor was in the range 100‐200, while the CO 2 permeance was in the range 0.1‐1.5 cm 3 (STP)/(cm 2 min atm). The results suggest that controlling the membrane pore size and method of activation of amine groups are the most critical factors for improving the CO2-permselectivity of the membrane. © 2004 Elsevier B.V. All rights reserved.

We present a new approach for rapid formation of mesoporous, surfactant-templated silica membranes on coarse-pore α-Al 2 O 3 ceramic supports. A surfactant-silica sol is dispersed in the gas phase in the form of small droplets and delivered to the surface of the planar support by a N 2 carrier stream. Coalescence of deposited sol droplets combined with solvent evaporation-induced self-assembly of liquid crystalline mesophases results in the formation of continuous, mesostructured silica-surfactant layers covering the surface of the support. These mesostructured silica membranes are impermeable right after synthesis and exhibit N 2 permeance in the range 10 −7 –10 −6 mol m −2 s −1 Pa −1 after surfactant removal. SEM studies revealed the presence of relatively smooth layers of thickness ∼1 μm on the surface of the ceramic supports while SAXS and TEM investigations revealed that these membranes possess cubic-ordered mesopores of size ∼20 A, without preferential orientation with respect to the substrate. Such membranes may find application in ultrafiltration separation processes, since surfactant-templating can be used for accurate control of the pore size/distribution in the proper range for a desired separation.

A novel and efficient method for molecular engineering of the pore size and porosity of microporous sol–gel silica membranes is demonstrated in this communication. By adding a suitable organic template (e.g. tetraethyl- or tetrapropylammonium bromide) in polymeric silica sols, otherwise known to result in microporous membranes with pores in the range 3–4 A, we can ‘shift’ the pore size to 5–6 A, as judged by single-component gas and vapor permeation results with probe molecules of increasing kinetic diameter (dk). The templated membranes exhibit permeances as high as 10 −7 to 10 −6 mol m −2 s −1 Pa −1 for molecules with dk < 4.0 A (e.g. CO2 ,N 2 ,C H 4), coupled with single-component selectivities of 100–1800 for N2/SF6, 20–40 for n-butane/iso-butane, and 10–20 for para-xylene/ortho-xylene. The transport properties of the templated membranes are distinctly different from those of the respective silica membranes prepared without templating, and resemble somewhat the transport properties of polycrystalline zeolite MFI membranes prepared by the lengthy, batch hydrothermal synthesis approach, using tetrapropylammonium bromide as a structure directing agent. © 2003 Elsevier Science B.V. All rights reserved.

We summarize and discuss recent results on the separation of close-boiling hydrocarbon mixtures by means of zeolite membranes. We focus on the separation of xylene isomers using silicalite (MFI) membranes, as well as several other hydrocarbon mixtures using faujasite membranes. In the case of the silicalite membranes, the selectivity is found to depend on the membrane microstructure. Permeation of xylene isomers through the silicalite membranes occurs through both zeolitic and non-zeolitic (intercrystalline) nanopores. This hypothesis is supported by vapor-phase permeation results on silicalite membranes synthesized with different microstructures, and by confocal microscopy experiments. In addition, a simple method for repairing calcination-induced membrane defects is presented, and its application is found to be essential in obtaining high (20–300) p -xylene/ o -xylene separation factors. The faujasite membranes are found to have high selectivities (40–150) in the separation of binary mixtures containing one aromatic component, and modest selectivities (4–9) for the separation of unsaturated from saturated low-molecular-weight hydrocarbons.

Zeolite MFI membranes with thickness 15–20 μm were grown on the surface of macroporous α-alumina and stainless steel support tubes (pore size 200 and 500 nm, respectively) by the secondary (seeded) growth technique. The tubular supports were dipped vertically in an aqueous suspension of colloidal silicalite-1 seed crystals (particle size 100 nm) and withdrawn at a speed of 1–2 cm/h to allow for uniform formation of seed layers on the outer (for stainless steel) or inner (for α-alumina) cylindrical surface of the support tubes. The seeded tubes were treated hydrothermally with clear solutions of different composition and the resulting MFI membranes were characterized by SEM and permeation of butane isomers. For the best preparations, binary n-butane/isobutane ratios at 22°C were as high as 28 and 53 for stainless steel and α-alumina tubes, respectively, while the n-butane permeation flux varied in the range 0.8–3.8 mmol m−2 s−1. The effect of temperature and feed partial pressure on permeation flux was also studied for binary mixtures of butane isomers and was found similar to that of planar membranes developed previously on α-alumina support disks by the same synthesis procedure.

Faujasite type zeolite membranes were synthesized on porous ceramic alumina supports by using direct (in situ) and secondary (seeded) growth methods. In the secondary growth method a seed layer of ZSM-2 nanocrystals (prepared according to a report by Schoeman et al. J. Colloid Interface Sci. 1995, 170, 449–456) was deposited on the surface of the support before the hydrothermal growth. For both in situ and secondary growth, the mixture composition was 4.17 Na 2 O:1.0 Al 2 O 3 :10 TEA (triethanol ammonium):1.87 SiO 2 :460 H 2 O. X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron microprobe analysis (EPMA), indicate well intergrown 5–30 μm thick FAU films with Si/Al ∼1–1.5. The separation of saturated/unsaturated hydrocarbon mixtures is demonstrated over a range of temperatures (40–160°C). The mixtures examined (and the corresponding equimolar mixture separation factors) are benzene/cyclohexane (160), benzene/ n -hexane (144), toluene/ n -heptane (45), propylene/propane (6.2), and ethylene/methane (8.4). In all cases, the membranes are unsaturated hydrocarbon permselective. With equimolar feed mixtures (5 kPa/5 kPa benzene/cyclohexane) and in the temperature range 65–160°C, the membranes exhibit separation factor of 20–160 with the benzene flux in the range 10 −4 –10 −3 mol m −2 s −1 . Decreasing the total feed partial pressure (0.31/0.31 kPa benzene/cyclohexane) reduces both separation factor (12) and benzene flux. Similar trend is observed when the benzene/cyclohexane ratio in the feed mixture (0.5/9.5 kPa benzene/cyclohexane) is reduced. A sorption diffusion model based on the Stefan–Maxwell formulation has also been employed to show that the benzene/cyclohexane separation can mainly be attributed to differences of their adsorption properties.

Fluorescence confocal optical microscopy (FCOM) was used to characterize MFI membranes made by secondary (seeded) growth. It is demonstrated that FCOM is a powerful tool for the non-destructive evaluation of zeolite membranes. This technique can provide two-dimensional, optical sections of the membranes with submicron resolution without physical damage to the sample. When contrasted with fluorescein-Na salt, it is shown that the grain boundary network in MFI membranes can be observed along the thickness of the membranes. Moreover, defects that do not propagate to the membrane surface and, therefore, are not detected by SEM, can be clearly imaged. One example of such a defect are internal cracks in the membrane.

Oriented MFI membranes made by secondary growth on the surface of α-Al2O3 support disks have been evaluated for the separation of xylene isomers vapors in the temperature range 22−275 °C and feed partial pressures up to ∼0.7−0.9 kPa. It is found that the separation performance of these membranes is directly related to the synthesis conditions and the resulting membrane microstructure. Thick (12−18 μm) and c-oriented membranes (type A membranes) made by 24-h growth at 175 °C exhibit single-component p-xylene/o-xylene permselectivity as high as 150 at 100 °C but very modest separation factors (usually

Zeolite MFI membranes with thicknesses in the range of 1–40 μm have been prepared by hydrothermal growth of colloidal silicalite-1 seed crystals of particle sizes ∼100 nm deposited on the surface of α-Al2O3 porous support disks. These membranes exhibit attractive separation characteristics as judged by permeation measurements with butane and xylene isomers. At 22°C, the permeation flux of n-butane and the n-butane/isobutane ratio from 50 kPa/50 kPa binary mixtures vary in the range of 1.0–4.0 mmol m−2 s−1 and 30–70, respectively. The n-butane flux exhibited a dependence on temperature and feed partial pressure consistent with activated diffusion of an adsorbed phase obeying Langmuir isotherm but was rather insensitive to the membrane thickness. For the best membranes, the single-component p-xylene flux and the p-xylene/o-xylene flux ratio at 100°C was in the range of 10–30 μmol m−2 s−1 and 30–130, respectively. The permeation flux of o-xylene increases dramatically in the presence of p-xylene resulting in a substantial loss in para/ortho selectivity (maximum of ∼5), an effect that may be attributed to the flexibility of the MFI framework in the presence of molecules with a close fit to its framework. At 100°C para/ortho selectivities ( > 20) are observed when the p-xylene feed partial pressure is below 0.05 kPa.

Submicron thick continuous palladium–silver films were deposited by sputtering on mesoporous γ-alumina substrates from a target composed of 75% Pd and 25% Ag. These membranes were tested in a multigas permeation system for hydrogen permeance and hydrogen selectivity over helium. Hydrogen permeance for the membrane used in the study was found to be in the range of 3 × 10 −8 to 1 × 10 −7 mol/m 2 s Pa and H 2 /He selectivities were in the range of 4–4000, depending mainly on Ag concentration and microstructure of the Pd–Ag films. A simple model based on the material balance concept has been developed to describe the transient composition behavior of the multicomponent sputter deposition process. The model is compared with experimental data over a range of deposition powers and target equilibration times. The results of the model agree well with experimental data. Both theoretical and experimental data show that deposition power and target equilibration are the most important variables affecting membrane composition.

Oriented MFI-type membranes made by secondary (seeded) growth exhibit potential for size-selective separation of p-xylene from its bulkier o- and m-xylene isomers, as judged by substantial single-component (up to 40) or mixture (up to 18) permeation flux ratios at 100 °C. However, increased permeation of the bulkier isomers, attributed to the flexibility of the MFI framework and resulting in lower selectivities, is observed under conditions of high temperature or high p-xylene loading in the MFI membranes.

A unique nanocrystalline, mesoporous PdO-SnO(2) film exhibiting high sensitivity and selectivity to hydrogen gas at room temperature has been developed.

Thin (0.5--5-{micro}m) palladium (Pd) membranes were prepared inside pores or on the surface of mesoporous (pore size 4--6 nm), sol-gel-derived {gamma}-Al{sub 2}O{sub 3} supports by the chemical vapor deposition (CVD) method using palladium acetylacetonate and palladium chloride (together with hydrogen) as Pd precursors. When Pd is deposited in the form of metal plugs inside pores of {gamma}-Al{sub 2}O{sub 3}, He permeance of the composite membranes increases exponentially with temperature, indicating activated diffusion through the microporous metal deposit defects, while only modest permselectivity for H{sub 2} is observed. When Pd is deposited in the form of a metal film on the surface of {gamma}-Al{sub 2}O{sub 3}, He permeance is governed by Knudsen-viscous flow through meso/macroporous metal film defects. The H{sub 2} permeance of different palladium membranes prepared by CVD appears to increase with palladium crystal grain size. The highest H{sub 2} permeance and H{sub 2}:He permselectivity for membranes prepared in this study are about 1.0--2.0 {times} 10{sup {minus}7} mol/m {center_dot} s {center_dot} Pa and 200--300 at 300 C, respectively.

Thin (0.1–1.5 μm) Pd and Pd Ag alloy membranes have been prepared on porous ceramic substrates consisting of a macroporous α-Al2O3 disk coated with a sol-gel derived, mesoporous γ-Al2O3 top layer. Metallorganic chemical vapor deposition (MOCVD) and magnetron sputtering were used to coat the thin metallic membranes employing Pd(II) acetylacetonate and a 75% Pd-25% Ag alloy target, respectively. The gas transport properties of the thin metallic membranes were determined by multicomponent permeation experiments with He, H2 and Ar at 25–300°C and 1 atm total pressure. The H2 permeance and H2: He selectivity were in the range 1.0–2.0 × 10−7 mol m−2 s−1 Pa−1 and 30–200 at 300°C, respectively. The dependence of H2 permeation rates on membrane thickness and temperature suggest that surface reaction steps are rate-limiting for H2 transport through the thin, ceramic-supported metallic membranes made by MOCVD and sputtering.

Thin ( 2 –Y 2 O 3 –CeO 2 membranes with different CeO 2 composition and membrane thickness were deposited on porous α-alumina substrates by the EVD process using corresponding metal chlorides as the precursors. CeO 2 composition in the membrane is the same as CeCl 3 concentration in the gas phase. The film growth rate for the EVD process is about 7 μm/h. The EVD prepared ZrO 2 –Y 2 O 3 –CeO 2 membranes do not show single phase, but consist of two separate phases: a ZrO 2 -dominant cubic phase and a CeO 2 -dominant cubic phase. Under present conditions (950–1050°C, P O 2 (high) =0.21 atm, P O 2 (low) =0.01 atm), oxygen permeation through the EVD prepared ZrO 2 –Y 2 O 3 –CeO 2 membranes is limited by the bulk diffusion in the membrane. The oxygen permeability of the ZrO 2 –Y 2 O 3 –CeO 2 membranes is in the range of 1–4×10 −11 mol/cm s, about an order of magnitude higher than that of ZrO 2 –Y 2 O 3 membranes. The oxygen permeation flux through the EVD prepared ZrO 2 –Y 2 O 3 –CeO 2 membrane increases with CeO 2 composition in the film.

Ultra-thin dense zirconia/yttria membrane composites were fabricated by EVD technique on porous α-alumina substrates. The deposited membranes consisted primarily of cubic/tetragonal phases as determined by XRD. The EVD film growth rate estimated by SEM photographs was 3–4 μm/h. Oxygen permeation data of thin dense zirconia/yttria membranes with different thickness (2–15 μm) were measured at 900 °C and 1000 °C. From the oxygen permeation data, the surface reaction and bulk diffusion rate parameters, α and β, were calculated. At 900 °C, α = 3.0 × 10 −8 mol/cm 2 · s · atm 1 2 and β = 3.0 × 10 −8 mol/cm · s · atm 1 4 with activation energy 53 KJ/mol and 72 KJ/mol for α and β, respectively. Presence of steam in the high oxygen partial pressure side promoted electrochemical surface reaction.

A thin, gas-tight palladium (Pd) membrane was prepared by the counter-diffusion chemical vapor deposition (CVD) process employing palladium chloride (PdCl2) vapor and H2 as Pd precursors. A disk-shaped, two-layer porous ceramic membrane consisting of a fine-pore γ-Al2O3 top layer and a coarse-pore α-Al2O3 substrate was used as Pd membrane support. A 0.5–1 μm thick metallic membrane was deposited in the γ-Al2O3 top layer very close to its surface, as verified by XRD and SEM with a backscattered electron detector. The most important parameters that affected the CVD process were reaction temperature, reactants concentrations and top layer quality. Deposition of Pd in the γ-Al2O3 top layer resulted in a 100- to 1000-fold reduction in He permeance of the porous substrate. The H2 permeation flux of these membranes was in the range 0.5–1.0 × 10−6 mol m−2 s−1 Pa−1 at 350–450°C. The H2 permeation data suggest that surface reaction steps are rate-limiting for H2 transport through such thin membranes in the temperature range studied.

We present a theoretical analysis of permeation through composite bi-layer materials with an irregular interface. The conservation of mass equation for the permeating species is solved using both approximate analytic and numerical techniques. The approximate analytic solution is valid for small deviations of the interface from planarity. To assess the accuracy of the analytic solution, the analytic solution is compared to numerical approximations for a wide range of composite geometries and relative material permeabilities. The analytic solution proves to be accurate and easy to use. The analysis demonstrates that a composite material with an irregular interface possesses a higher permeability and slightly lower selectivity than an equivalent composite with a flat interface. Furthermore, the changes in permeability depend strongly on the magnitude of the interface irregularity but are relatively insensitive to the relative thickness of the two layers.

Explicit equations correlating chemical vapor deposition (CVD) conditions and substrate parameters to the deposition zone thickness, location of maximum deposition, and pore size evolution of a modified counterdiffusion CVD process (MCVD) are derived from recently developed semianalytical solutions. The permeability reduction ratio and the substrate average pore size as a function of deposition time are calculated using the semianalytical solutions and substrate pore size distribution data. Recently reported experimental data of CVD of ZrO[sub 2], TiO[sub 2], and Al[sub 2]O[sub 3] in porous substrates are compared with the theoretical results in terms of the location of maximum deposition, deposition zone thickness, permeability reduction ratio, change in average pore size, and pore closure time. The theoretical results agree reasonably well with the experimental findings and provide an improved insight into the MCVD process for ceramic membrane fabrication.

A theoretical analysis of modified chemical vapor deposition (MCVD) of solid oxides in porous media for ceramic membrane preparation and/or modification is presented in this paper. Semi-analytical solutions have been obtained to describe the evolution of solid deposit profiles inside porous substrates, using a phenomenological model that takes into account intrapore precursor diffusion, chemical reaction and pore geometry change. Explicit equations have been derived which correlate the three main deposition characteristics, deposit location, deposit zone thickness and pore closure time to the CVD experimental parameters and substrate pore structure. Such explicit equations provide better insight into this unique CVD process for advanced materials synthesis and are very useful in practical applications. A comparison of the semi-analytical solutions with a numerical solution based on the finite element method is also presented. The semi-analytical solutions are in good agreement with the numerical solutions, especially under the conditions used for ceramic membrane preparation and/or modification.

Synthetic solid-state nanopores are being intensively investigated as single-molecule sensors for detection and characterization of DNA, RNA and proteins. This field has been inspired by the exquisite selectivity and flux demonstrated by natural biological channels and the dream of emulating these behaviours in more robust synthetic materials that are more readily integrated into practical devices. So far, the guided etching of polymer films, focused ion-beam sculpting, and electron-beam lithography and tuning of silicon nitride membranes have emerged as three promising approaches to define synthetic solid-state pores with sub-nanometre resolution. These procedures have in common the formation of nominally cylindrical or conical pores aligned normal to the membrane surface. Here we report the formation of ‘kinked’ silica nanopores, using evaporation-induced self-assembly, and their further tuning and chemical derivatization using atomic-layer deposition. Compared with ‘straight through’ proteinaceous nanopores of comparable dimensions, kinked nanopores exhibit up to fivefold reduction in translocation velocity, which has been identified as one of the critical issues in DNA sequencing. Additionally, we demonstrate an efficient two-step approach to create a nanopore array exhibiting nearly perfect selectivity for ssDNA over dsDNA. We show that a coarse-grained drift–diffusion theory with a sawtooth-like potential can reasonably describe the velocity and translocation time of DNA through the pore. By control of pore size, length and shape, we capture the main functional behaviours of protein pores in our solid-state nanopore system. Synthetic solid-state nanopores are of interest at present for their use as single-molecule sensors for characterization and detection of biomolecules. By using self-assembly evaporation and atomic-layer deposition, kinked silica nanopores are shown to exhibit reduction in DNA-translocation velocity and selectivity.

CO{sub 2} captured from coal-fired power plants represents three-quarters of the total cost of an entire carbon sequestration process. Conventional amine absorption or cryogenic separation requires high capital investment and is very energy intensive. Our novel membrane process is energy efficient with great potential for economical CO{sub 2} capture. Three classes of microporous sol-gel derived silica-based membranes were developed for selective CO{sub 2} removal under simulated flue gas conditions (SFG), e.g. feed of 10% vol. CO{sub 22} in N{sub 2}, 1 atm total pressure, T = 50-60 C, RH>50%, SO2>10 ppm. A novel class of amine-functional microporous silica membranes was prepared using an amine-derivatized alkoxysilane precursor, exhibiting enhanced (>70) CO{sub 2}:N{sub 2} selectivity in the presence of H{sub 2}O vapor, but its CO{sub 2} permeance was lagging (

A molecular-scale interpretation of interfacial processes is often downplayed in the analysis of traditional water treatment methods. However, such an approach is critical for the development of enhanced performance in traditional desalination and water treatments. Water confined between surfaces, within channels, or in pores is ubiquitous in technology and nature. Its physical and chemical properties in such environments are unpredictably different from bulk water. As a result, advances in water desalination and purification methods may be accomplished through an improved analysis of water behavior in these challenging environments using state-of-the-art microscopy, spectroscopy, experimental, and computational methods.

We report atomic layer deposition of an ultrathin hybrid organic/inorganic film on a porous support and its conversion to a high flux, high selectivity membrane. Through chemical passivation of the internal support porosity and remote oxygen plasma activation of the support surface, ALD of a bis(triethoxysilyl)ethane precursor is confined to the immediate surface of the support, allowing formation of a 5 nm thick film spanning the underlying porosity. UV/ozone removal of the C2 porogen creates a microporous membrane with a He/SF6 selectivity >104 and a substantial He flux of 5.3 sccm/bar·cm2. Prior to conversion, these ultrathin films are of interest as low k dielectric sealing layers. Use of bridging ligands with other shapes and sizes should enable generalization of this approach to other demanding separation problems.

We report the synthesis and characterization of mesostructured thin silica films derived from methyltriethoxysilane (MTES) and/or tetraethyl orthosilicate (TEOS) silica precursors and polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymers via the solvent evaporation-induced self-assembly (EISA) process. It is found that the meso- and microstructure of the calcined films consists of cubic-ordered arrays of spherical mesopores of 5−7 nm in diameter, interconnected with a small number (≤4% by volume) of PEO-induced micropores of ∼1 nm in diameter, as determined by new experimental results of transmission electron microscopy, N2 sorption, gas permeation, and grazing incidence small-angle X-ray scattering studies. The present comprehensive study of these novel closed-pore films should provide a general methodology for microstructural characterization of other related porous films prepared by similar self-assembly processes.

Conjugated polymer/silica nanocomposites with hexagonal, cubic, or lamellar mesoscopic order were synthesized by self-assembly using polymerizable amphiphilic diacetylene molecules as both structure-directing agents and monomers. The self-assembly procedure is rapid and incorporates the organic monomers uniformly within a highly ordered, inorganic environment. By tailoring the size of the oligo(ethylene glycol) headgroup of the diacetylene-containing surfactant, we varied the resulting self-assembled mesophases of the composite material. The nanostructured inorganic host altered the diacetylene polymerization behavior, and the resulting nanocomposites show unique thermo-, mechano-, and solvatochromic properties. Polymerization of the incorporated surfactants resulted in polydiacetylene (PDA)/silica nanocomposites that were optically transparent and mechanically robust. Molecular modeling and quantum calculations and (13)C spin-lattice relaxation times (T(1)) of the PDA/silica nanocomposites indicated that the surfactant monomers can be uniformly organized into precise spatial arrangements prior to polymerization. Nanoindentation and gas transport experiments showed that these nanocomposite films have increased hardness and reduced permeability as compared to pure PDA. Our work demonstrates polymerizable surfactant/silica self-assembly to be an efficient, general approach to the formation of nanostructured conjugated polymers. The nanostructured inorganic framework serves to protect, stabilize, and orient the polymer, mediate its performance, and provide sufficient mechanical and chemical stability to enable integration of conjugated polymers into devices and microsystems.

This chapter is divided into four sections the first of which treats issues of general relevance to Chemical Vapor Deposition (CVD) of membranes, the second reviews work on dense silica membranes, the third is devoted to Y_2O_3-stabilized ZrO_2 (YSZ) membranes, and the fourth treats CVD of Pd membranes.