Self-standing Membranes Research Articles

Formation of silica nanofibers with hierarchical structure via electrospinning

Self-standing thiol-functionalized fibrous membrane with bimodal pore structure was successfully fabricated through the combination of electrospinning and surfactant-directing pore formation technique. We also found that the interference of electric field as well as the rapid solvent evaporation during the electrospinning process has a negative effect on the formation of ordered mesoporous structures. As high-performance adsorption-based filtration system, such hierarchically structured membrane is found to efficiently remove Cu (II) ions under high flux.

Self-standing nanoparticle membranes and capsules

We perform coarse-grained molecular dynamics simulations of self-standing nanoparticle membranes observed in recent experiments (K. E. Mueggenburg et al., Nat. Mater., 2007, 6, 656). In order to make our simulations feasible, we model 2-3 times smaller gold nanoparticles (core radius of r(core) ≈ 0.8 nm) covered with alkanethiol ligands (length of l(ligand) ≈ 0.5-2.6 nm). We study the structure, stability, and mechanical properties of these membranes and show that these characteristics are controlled by the ratio of R(LC) = l(ligand)/r(core). For R(LC) ≈ 0.6, the ligated nanoparticles form well ordered monolayers with hexagonal packing, in agreement with the experiments (R(LC) ≈ 0.44). For R(LC) ≈ 1.6, the nanoparticles form less organized multilayers, which are more stable and flexible. We show that these membranes could potentially form stable capsules for molecular storage and delivery.

Large-Scale Colloidal Self-Assembly by Doctor Blade Coating

This article reports a simple, roll-to-roll compatible coating technology for producing 3D highly ordered colloidal crystal-polymer nanocomposites, colloidal crystals, and macroporous polymer membranes. A vertically beveled doctor blade is utilized to shear align silica microsphere-monomer suspensions to form large-area nanocomposites in a single step. The polymer matrix and the silica microspheres can be selectively removed to create colloidal crystals and self-standing macroporous polymer membranes. The thickness of the shear-aligned crystal is correlated with the viscosity of the colloidal suspension, and the coating speed and the correlations can be qualitatively explained by adapting the mechanisms developed for conventional doctor blade coating. We further demonstrate that the doctor blade coating speed can be significantly increased by using a dual-blade setup. The optical properties of the self-assembled structures are evaluated by normal-incidence reflection measurements, and the experimental results agree well with the theoretical predictions using Bragg's law and a scalar wave approximation model. We have also demonstrated that the templated macroporous polymers with interconnected voids and uniform interconnecting nanopores can be directly used as filtration membranes to achieve size-exclusive separation of particles.

Optical resolution with membranes derived from marine polymers

Optical resolution with membranes derived from marine polymersNovel polyion-lipid complexes were prepared from quaterinized chitosan (QCh), which was a derivative of marine (natural) polymer, and three types of anionic amphiphile, such as sodium 1-dodecanesulfate (C12SNa), sodium 1-tetradecanesulfate (C14SNa), and sodium 1-hexadecanesulfate (C16SNa). Those complexes gave durable self-standing membranes. The QCh-lipid complex membranes prepared in the present study showed chiral separation ability; in other words, they selectively transported L-Lys from racemic mixture of Lys adopting a concentration gradient as a driving force for membrane transport. Permselectivity of QCh-C12S membrane toward L-Lys was determined to be 3.31 under the concentration difference of 1.0 × 10−3 mol dm−3. From transport experiments and adsorption studies, it was revealed that the permselectivity was dominantly determined by diffusivity selectivity. It is expected that the present study would open a door to novel materials.

Fast optical vapour sensing by Bloch surface waves on porous siliconmembranes

The coupling of optical Bloch surface waves at the truncated end of one dimensional porous silicon photonic crystals is exploited for fast vapour sensing. Self-standing multilayered membranes bound to transparent substrates were fabricated by electrochemical etching and used in an attenuated total reflection configuration to resonantly excite the surface waves and perform real-time sensing.

Synthesis of proton conductive membranes based on inorganic–organic hybrid structure bound with phosphonic acid

Proton conductive inorganic–organic hybrid membranes were synthesized from styrene derivatives of alkoxysilane and ethyl 2-[3-(dihydroxyphosphonyl)-2-oxopropyl] acrylate (EPA) through copolymerization followed by sol–gel reaction. Self-standing, homogeneous and transparent hybrid membranes with chemically bound phosphonic acid groups were synthesized. FT-IR analysis exhibited the hybrid membranes included phosphonic acid groups. 13C and 29Si NMR studies indicated that alkoxysilyl functionalized styrene derivatives were not only copolymerized with EPA but also condensed yielding Si–O–Si linkages by sol–gel reaction. TG–DTA analysis revealed that these membranes were thermally stable up to 200 °C in dry O 2. The proton conductivities of the hybrid membranes increased with phosphonic acid content and temperature. The P/Si ratio of the membrane was dependent on the number of alkoxy group in the starting alkoxysilane. The hybrid membrane from (dimethylmethoxysilylmethyl)styrene (DMMSMS(M))/EPA = 1/6 revealed proton conductivities of 6.3 × 10 −3 and 2.4 × 10 −4 S cm −1 at 68.0% relative humidity and 18.8% relative humidity, respectively, at 140 °C.

Synthesis of hyperbranched copolyimides and their application as selective layers in composite membranes

Self-standing dense membranes from hyperbranched copolyimides based on (hexafluoroisopropylidene)diphthalic anhydride (6FDA), 1,3,5-tris(4-aminophenoxy)benzene (TAPOB) and 4,4′-(hexafluoroisopropylidene)dianiline (6FpDA) were successfully prepared and characterized for physicochemical properties. The synthesis involved the formation of hyperbranched poly(amic acid) precursors in the first step and their thermal imidization in the second step. Molar ratio of comonomers was 0.95:1 for 6FDA-TAPOB polyimide and 0.95:0.5:0.5 for 6FDA-6FpDATAPOB copolyimide. No gelation occurred during polymerizations if the concentration of resulting polymer was kept below 4 wt.%. Prepared polyimides showed moderate molecular weights ( M w ∼ 37,000), 6FDA-6FpDA-TAPOB copolyimides showed significantly broader polydispersity index (4.3) then for 6FDA-TAPOB poylimide (1.9). Both polymers exhibited similar glass transition temperatures ( T g ∼ 230°C) and 10 wt.% loss temperatures T 10 ∼ 505°C). Gas transport measurements showed significantly higher permeability coefficients for 6FDA-6FpDA-TAPOB [ P(H 2) = 33 Barrer; P(N 2) = 0.59 Barrer] copolyimide than for 6FDA-TAPOB [ P(H 2) = 6.8 Barrer; P(N 2) = 0.06 Barrer]. Ideal selectivities were significantly higher for 6FDA-TAPOB [α(H 2/CH 4) = 228, α(O 2/N 2) = 6.4] than for 6FDA-6FpDA-TAPOB [α(H 2/CH 4) = 112, α(O 2/N 2) = 5.9]. Novel composite membranes based on these hyperbranched (co)polyimides (applied as selective layer) were successfully prepared. Preparation was made by dip-coating of poly(acrylonitrile) porous supports. Selective layers were covered with additional PDMS layer to seal possible microdefects and for protection. Both composite membranes showed moderate single gas fluxes [ J(H 2) = 0.28 m 3 (STP) m −2 h −1 bar −1 for 6FDA-6FpDA-TAPOB] and selectivities were about 65–75 % lower than corresponding dense membranes. Composite membrane with 6FDA-6FpDA-TAPOB selective layer exhibited slightly better separation performance than that one based on 6FDATAPOB. In further work we plan to optimize the parameters of composite membrane preparation process to achieve better separation performance.

Polymeric Pseudo-Liquid Membranes from Poly(2-ethylhexyl methacrylate)

Novel liquid membranes, which are named polymeric pseudo-liquid membranes, were constructed, using poly(2-ethylhexyl methacrylate), which showed rubbery state under operation conditions, as a membrane matrix. Dibenzo-18-crown-6 (DB 18C6) was adopted as a model transporter and membrane transport performance through those polymeric pseudo-liquid membranes was investigated, adopting KCI as a model substrate. Poly(2-ethylhexyl methacrylate), P2EHMA, gave self-standing liquid membranes under the experimental conditions, of which operation temperature was above its glass transition temperature. The polymeric pseudo-liquid membranes showed transport ability of KCI. The flux value was linearly increased with the increase in DB 18C6 content in the membrane and the membrane transport ability was greatly dependent on not only the molecular weight of membrane matrix, P2EHMA, but also the operation temperature. The present paper suggested that polymeric pseudo-liquid membranes are applicable to membrane separation as one of liquid membrane transport systems.

Fabrication of Porous Supported MIEC Dense Thin Coating for Hydrogen Separation

Decomposition of steam under a chemical driving force at moderate temperatures offers a simple and economical way to generate hydrogen. Significant amounts of hydrogen can be separated by splitting steam and removing the oxygen using Gd0.2Ce0.8O1.9-Gd0.08Sr0.88Ti0.95Al0.05O3{plus minus}δ mixed ionic and electronic conductors. Hydrogen generation experiments for the self-standing thick membranes and porous supported thin membranes have been conducted at different oxygen pressure gradients across the membranes and steam contents on the steam side. Experimental results indicate that the hydrogen generation process is controlled by the bulk diffusion for the thick membranes, while the permeation process for the thin membranes is mixed controlled, i.e. the process is controlled by surface exchange reactions and the oxygen bulk diffusion. A mathematical model for the calculation of the area specific hydrogen generation rate is proposed based on the measured oxygen partial pressures, gas compositions of the inlet and outlet gases on the steam side.

Self-Standing Proton-Conducting Polymer Membrane

Robust polymer films capable of conducting protons have potential for utilization in applications such as fuel cells. The authors report novel block copolymers containing various ratios of pendant perfluorobenzene moiety for thermal stability, 1-methylsilacyclobutyl group for cross-linking, and sulfonic acid for proton conduction. The polymers display high ion-exchange capacity and proton conductivities similar to that of Nafion 117.

Facile fabrication of a novel high performance CO 2 separation membrane: Immobilization of poly(amidoamine) dendrimers in poly(ethylene glycol) networks

Poly(amidoamine) (PAMAM) dendrimers showed high CO 2 separation properties and were successfully immobilized in a poly(ethylene glycol) (PEG) network upon photopolymerization of PEG dimethacrylate. The PAMAM dendrimer incorporation ratio was readily controlled, and a stable self-standing membrane containing up to 75 wt.% PAMAM dendrimer was obtained. The CO 2 separation properties over smaller H 2 were investigated by changing the PAMAM dendrimer content or generation and CO 2 partial pressure ( Δ P C O 2 ) under atmospheric conditions. Especially, a polymeric membrane containing 50 wt.% PAMAM dendrimer (0th generation) exhibited an excellent CO 2/H 2 selectivity of 500 with CO 2 permeability of 2.74 × 10 −14 m 3(STP)m/(m 2 s Pa) or 3.65 × 10 3 barrer (1 barrer = 7.5 × 10 −18 m 3(STP)m/(m 2 s Pa)) when a mixture gas (CO 2/H 2: 5/95 by vol.) was fed at 25 °C and 100 kPa with 80% relative humidity. This polymeric materials are promising for a novel CO 2 separation membrane.

Resolution Enhancement of Extreme Ultraviolet Microscope Using an Extreme Ultraviolet Beam Splitter

We developed the extreme ultraviolet (EUV) beam splitter, which is a critical component for resolution enhancement, to achieve the uniform numerical aperture (NA) for all planar directions in the EUV microscope. In the fabrication of the EUV beam splitter, stress control of the Mo/Si multilayer is a necessary to achieve a self-standing membrane of the Mo/Si multilayer. We succeeded with the stress control by optimizing RF power, DC power, and argon working pressure during Mo/Si multilayer deposition. A large effective area of 8×10 mm2, reflectivity of 27%, and transmittance of 17% were achieved simultaneously. Furthermore, by installing the EUV beam splitter in stead of a turning mirror of Schwarzschild optics (SCO), the NA of the SCO became the same in the horizontal and vertical directions on a sample plane. Thus, the 300-nm line and space elbow pattern on an EUV mask for all planar directions was clearly resolved. We have developed an EUV microscope with an EUV beam splitter and succeeded in the highly precise pattern inspection.

Proton conductive inorganic–organic hybrid membranes prepared from 3-aminopropyltriethoxysilane and phosphoric acid by the sol–gel method

Proton conductive inorganic–organic hybrid membranes with acid–base pairs have been prepared from 3-aminopropyltriethoxysilane and phosphoric acid by the sol–gel method. The self-standing membranes obtained are represented as poly(3-aminopropylsilsesquioxane)-H 3PO 4 (PAPS–H 3PO 4) membranes. Infrared absorption spectra of the PAPS–H 3PO 4 films showed that amino groups of PAPS were protonated by phosphoric acid, indicating the formation of acid–base pairs. X-ray diffraction patterns of the PAPS–H 3PO 4 membranes showed diffraction peaks attributed to hexagonal structure, which is probably formed by stacking of rodlike polysiloxane with the acid–base pairs extruded outside. The conductivities of the PAPS–H 3PO 4 membranes with a molar ratio of H 3PO 4/APTES = 1.0 was 4 × 10 − 4 S cm − 1 at 150 °C under dry condition.

Preparation of a self-standing mesoporous carbon membrane with perpendicularly-ordered pore structures

A self-standing mesoporous carbon membrane (sOMC) with perpendicularly-ordered pore structures was prepared through a simple synthetic method; the pores with a diameter of 8 nm were well ordered over a large area and perpendicularly-oriented to the surface without any external field; in the formation of this ordered structure, the drying process is key, and a porous alumina support is important to induce drying.

TiO2 Nanotube Arrays of 1000 μm Length by Anodization of Titanium Foil: Phenol Red Diffusion

We report for the first time fabrication of self-aligned hexagonally closed-packed titania nanotube arrays of over 1000 μm in length and aspect ratio ≈10 000 by potentiostatic anodization of titanium. We describe a process by which such thick nanotube array films can be transformed into self-standing, flat or cylindrical, mechanically robust, polycrystalline TiO2 membranes of precisely controlled nanoscale porosity. The self-standing membranes are characterized using Brunauer−Emmett−Teller surface area measurements, glancing angle X-ray diffraction, and transmission electron microscopy. In initial application, such membranes are used to control the diffusion of phenol red.

SPPSU-based hybrid proton conducting polymeric electrolytes for intermediate temperature PEMFCs

Polyphenylsulfone (PPSU) was reacted with SiCl 4 to afford silylated telechelic polymers having different inorganic content, which were sulfonated to different degrees (0.05 ≤ DS ≤ 2) using H 2SO 4 or ClSO 3Si(CH 3) 3. A class II organic–inorganic hybrid polymer was then synthesized via cross-linking through Si–O–Si bonds generated by non-hydrolytic sol–gel reactions. The physicochemical properties of the hybrid were suitable for the preparation of self-standing, flexible and homogeneous membranes which were characterized ATR/FTIR spectroscopy demonstrating the formation of covalent bonds between the organic and inorganic components and the absence of dispersed inorganic silicon. The electrochemical performance was analyzed by electrochemical impedance spectroscopy which showed adequately high conductivity values to make the hybrid polymer a suitable candidate for application as electrolyte in PEMFCs operating at T > 100 °C.

Synthesis and properties of a polyimide containing pendant sulfophenoxypropoxy groups

A novel sulfonated polyimide having pendant sulfophenoxypropoxy groups was synthesized, and its electrolyte properties were investigated for fuel-cell applications. A diamine monomer was synthesized from 3,3′-dihydroxybenzidine in four steps, and its polymerization was performed with 1,4,5,8-naphthalenetetracarboxylic dianhydride in the presence of triethylamine and benzoic acid in m-cresol. A flexible, ductile, and self-standing membrane was obtained via casting from an m-cresol solution. Good thermal, hydrolytic, and oxidative stability was confirmed. The ionomer membrane showed very high proton conductivity of 1.0 S cm−1 at 120 °C and 100% relative humidity, which is higher than that of a Nafion membrane.

Preparation of Self-Standing Composite Electrolyte Membrane by Use of Three-Dimensionally Ordered Macroporous Silica Matrix

Three kinds of sulfonated polymer electrolytes (PAMPS, SPEES, and SPI) have been synthesized and evaluated as filling polymers for a three-dimensionally ordered macroporous (3DOM) silica membrane. The 3DOM composite membrane exhibited excellently high dimensional stability regardless of the kind of filling polymers due to a suppression of polymer expansion by the hard silica matrix. Accordingly, a low methanol cross- over could be attained in the composite membrane with high proton conductivity.

Preparation of Self-Standing Composite Electrolyte Membrane by Use of Three-Dimensionally Ordered Macroporous Silica Matrix

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Chiral separation membranes from modified polysulfone having myrtenal-derived terpenoid side groups

Novel polymeric materials, having a chiral environment, were obtained by the reaction of lithiated polysulfone with chiral terpenoid myrtenal. The resulting polymers gave self-standing durable membranes. Molecularly imprinted membranes were prepared from the novel myrtenal-containing polysulfones by the presence of print molecules during the membrane preparation process. The d-isomer imprinted membrane showed d-isomer adsorption and diffusivity selectivity, and vice versa. As a result, the d-isomer imprinted membrane transported the d-isomer in preference to the l-isomer, and vice versa. The control non-imprinted membrane also showed permselectivity toward racemic glutamic acid mixtures. The expression of permselectivity for the molecularly imprinted membranes was synergistically due to adsorption and diffusivity selectivity.