Anodic alumina membranes with defined pore diameters and thicknesses obtained by adjusting the anodizing duration and pore opening/widening time

The through-hole porous anodic aluminum oxide (AAO) membranes were fabricated by a simple two-step anodization of aluminum in 0.3 M oxalic acid, 0.3 M sulfuric acid, and 2 wt.% phosphoric acid solutions under different operating conditions followed by the removal of the remaining Al substrate and the pore opening/widening process. The effect of duration of the second anodizing step on the thickness of the porous oxide layer and the influence of other anodizing conditions such as applied voltage, type of electrolyte, and purity of the substrate on the rate of porous oxide growth were discussed in detail. The pore opening procedure for all synthesized membranes was optimized, and the influence of the duration of chemical etching on structural features of AAO membranes, especially pore diameter, was studied. The rate of pore widening was established for AAO membranes formed in various anodizing electrolytes and for different temperatures of 5 wt.% H₃PO₄ used for alumina dissolution.

     

Characterization of highly porous polymeric materials with pore diameters larger than 100 nm by mercury porosimetry and X-ray scattering methods

Highly porous polymeric materials with pore sizes ranging from 100 nm to 1 microm are a very challenging class of materials not only to prepare synthetically (due to the high capillary pressures generated upon solvent removal) but also to characterize structurally. Through the examples of three different types of porous compounds synthesized in our laboratory (i) high-density melamine-based "MF-hd" with monomodal pore diameters around 500-900 nm, (ii) low-density melamine-based "MF-ld" with bimodal pore size distribution and average diameters around 2.3 microm and 350 nm, (iii) highly porous polyurethane "PU" with monomodal pore sizes around 150 nm, we confirm the limitations of mercury porosimetry as a means to investigate the architecture of materials with very high porosity (>80 vol %) and low compressive strength. Instead, a combination of high-resolution scanning electron microscopy and small-angle and ultrasmall-angle X-ray scattering (SAXS and USAXS, respectively) studies of these three types of materials helps in determining both the network and the pore structures. This work elucidates the need and applicability of the SAXS/USAXS techniques in characterizing such porous materials. For instance, the polyurethane specimens can only be quantitatively characterized by scattering techniques, the results of which are corroborated by high-resolution scanning electron microscopy observations.     

Preparation of three-dimensionally ordered macroporous perovskite-type lanthanum-iron-oxide LaFeO3 with tunable pore diameters: High porosity and photonic property

Three-dimensionally ordered macroporous (3DOM) lanthanum-iron-oxide (LaFeO₃) with different pore diameters was prepared using a colloidal crystal of polymer spheres with different diameters as templates. Ethylene glycol-methanol mixed solution of metal nitrates was infiltrated into the void of the colloidal crystal template of a monodispersed poly(methyl methacrylate) (PMMA) sphere. Heating of this PMMA-metal salt-ethylene glycol composite produced the desired well-ordered 3DOM LaFeO₃ with a high pore fraction, which was confirmed by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), mercury (Hg) porosimetry, and ultraviolet-visible (UV-vis) diffuse reflectance spectra. 3DOM LaFeO₃ with pore diameters of 281 and 321 nm shows opalescent colors because of photonic stop band properties. Catalytic activity of the 3DOM LaFeO₃ for combustion of carbon particles was enhanced by a potassium cation, which was involved from K₂S₂O₈ used as a polymerization initiator.     

Pore formation in polyimide irradiated by high-energy ions and the properties of the obtained membranes

The optimum conditions are determined for etching latent Kr tracks in sodium hypochlorite solution to prepare polyimide track membranes (PI-TMs) with cylindrical pores and the electrosurface properties of the membranes are investigated. The stability of the porous structure of PI-TMs is studied at elevated temperatures (up to 250°C) in aggressive media (pH 1–12). It is shown that the porous structure of PI-TMs is characterized by enhanced chemical and thermal stability.     

Synthesis and properties of the polythiourethanes obtained by the cationic ring‐opening polymerization of cyclic thiourethanes

The cationic ring‐opening polymerization of a five‐membered thiourethane [3‐benzyl‐1,3‐oxazolidine‐2‐thione (BOT)] with boron trifluoride etherate afforded the corresponding polythiourethane with a narrow molecular weight distribution in an excellent yield. The molecular weight of the polymers could be controlled by the feed ratio of the monomer to the initiator. A kinetic study of the polymerization revealed that the polymerization rate of BOT (1.3 × 10^?2 L mol^?1 min^?1) was two times larger than that of the six‐membered thiourethane [3‐benzyltetrahydro‐1,3‐oxazolidine‐2‐thione (BTOT); 6.8 × 10^?3 L mol^?1 min^?1], and the monomer conversion obeyed the first‐order kinetic equation. These observations, along with the successful results in the two‐stage polymerization, supported the idea that this polymerization proceeded in a controlled manner. Block copolymerizations of BOT with BTOT were also carried out to afford the corresponding di‐ and triblock copolymers with narrow molecular weight distributions. The order of the 5% weight loss temperatures was as follows: poly(3‐benzyltetrahydro‐1,3‐oxazolidine‐2‐thione) [poly(BTOT)] > poly(BTOT₅₄‐b‐BOT₄₆) > poly(3‐benzyl‐1,3‐oxazolidine‐2‐thione) [poly(BOT)]. This indicated that an increase in the BTOT unit content raised the decomposition temperature. The order of the refractive indices was poly(BOT) > poly(BTOT₅₄‐b‐BOT₄₆) > poly(BTOT₅₄‐b‐BOT₄₆‐b‐BTOT₅₀) > poly(BTOT); this was in accord with the order of the sulfur content in the polymer chain. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4795–4803, 2006     

Preparation of carbon fibers/carbon/alumina tubular composite membranes and their applications in treating Cu-CMP wastewater by a novel electrochemical process

In this study, the alumina substrate was first prepared by the extrusion method, then followed by poly-vinylydenchloride (PVDC) film wrapping, PVDC carbonization, catalyst precursor coating, and the chemical vapor deposition (CVD) process to grow carbon fibers on the carbon interlayer. The carbon fibers/carbon/alumina tubular composite membranes (CCA-TCMs) thus obtained, with a pore size distribution ranging from 2 to 10 nm, were further characterized by scanning electron microscopy, transmission electron microscopy, and permporometry. A prepared CCA-TCM of this kind was incorporated into a novel simultaneous crossflow electrocoagulation and electrofiltration (EC/EF) treatment module to evaluate its capability in treating Cu-CMP (chemical mechanical polishing) wastewater. Crossflow EC/EF performance tests were carried out based on the 2³⁻¹ fractional factorial design using the electric field strength, crossflow velocity, and transmembrane pressure (TMP) as the experimental factors. Under the optimal operating conditions, the CCA-TCM associated EC/EF treatment module is capable of treating Cu-CMP wastewater in a proper manner. Permeate thus obtained had a turbidity of below 1 NTU and the removal efficiencies of total solids content, total organic carbon, copper, and silicon for Cu-CMP wastewater were 72%, 81%, 92%, and 87%, respectively.     

Streaming potential and surface charge density of microporous membranes with pore diameter in the range of thickness

A system formed by two phases bathing a microporous membrane is studied considering its behavior as a dynamic system. So, the natural frequencies for each used membrane is determined and then, applying a flow ramp with a rate sufficiently small, the streaming potential can be obtained from the slope of the pressure values versus electrical potential.The determination of the electric potential inside the pores, φ, requires to solve the Poisson–Böltzmann equation in the case of membranes with pore diameter in the range of thickness, for which the radial components of velocity of the fluid must be considered. Since there is no analytical solution, a numerical method was used to obtain φ. The electrical potential value at a distance equal to hydrodynamic radius from pore axis (zeta potential) is used to evaluate the streaming potential by the Helmholtz–Smoluchowsky relation. These values were compared with the experimental data accomplishing the suitable iterations over the surface charge density until coincidence.The values of the surface charge density for the studied membranes show a concentration dependence described by Langmuir’s model for the greatest pore diameters and Freundlich’s model for the smallest pore diameters.     

Ordered mesoporous silica with large cage-like pores: structural identification and pore connectivity design by controlling the synthesis temperature and time

FDU-1 silicas with large cage-like pores (diameter about 10 nm) were synthesized under acidic conditions from tetraethyl orthosilicate in the presence of a poly(ethylene oxide)-poly(butylene oxide)-poly(ethylene oxide) triblock copolymer template B50-6600 (EO(39)BO(47)EO(39)). High-resolution transmission electron microscopy and small-angle X-ray scattering provided strong evidence that FDU-1 silica synthesized under typical conditions is a face-centered cubic Fm3m structure with 3-dimensional hexagonal intergrowth and is not a body-centered cubic Im3m structure, as originally reported. Samples synthesized in a wide range of conditions (initial temperatures from 298 to 353 K; hydrothermal treatment at 333-393 K) exhibited similar XRD patterns and their nitrogen adsorption isotherms indicated a good-quality cage-like pore structure. The examination of low-pressure nitrogen adsorption isotherms for FDU-1 samples, whose pore entrance diameters were evaluated using an independent method, allowed us to conclude that low-pressure adsorption was appreciably stronger for samples with smaller pore entrance sizes. This prompted us to examine low-pressure adsorption isotherms for a wide range of samples and led us to a conclusion that the FDU-1 pore entrance size can be systematically enlarged from about 1.3 nm (perhaps even lower) to at least 2.4 nm without an appreciable loss of uniformity by increasing the temperature of the hydrothermal treatment or the initial synthesis. Further enlargement of pore entrance size was achieved for sufficiently long hydrothermal treatment times at temperatures of 373 K or higher, as seen from the shape of nitrogen desorption isotherms. This allowed us to obtain samples with uniform pore sizes, high adsorption capacity, and with pore entrances enlarged so much that their size was similar to the size of the pore itself, resulting in a highly open porous structure. However, in the latter case, there was evidence that the pore entrance size distribution was quite broad.     

Preparation and characterization of CuO/SiO2 and NiO/SiO2 with bimodal pore structure by sol-gel method

CuO/SiO₂ and NiO/SiO₂ with bimodal pore structure were prepared by sol-gel reactions of Tetra-methoxysilane (TMOS) and the respective metal nitrate in the presence of poly (ethylene oxide) (PEO) with an average molecular weight of 10 000 and the catalyst of acetic acid. In this process, the interconnected macroporous morphology was formed when transitional structures of spinodal decomposition were frozen by the sol-gel transition of silica. The addition of copper and nickel into the silica-PEO system had a negligible effect on the morphology formation. In gel formation, it was found that NiO crystalline sizes in the samples increased with decreasing Si/Ni molar ratio. It was considered that PEO interacted with both silica and nickel cations. In the CuO/SiO₂ with the presence of PEO_, CuO crystalline sizes were larger than those of NiO/SiO_2. It was considered that there was no obvious interaction between the Cu cation and PEO, most of the copper ions in wet silica gel were present in the outer solution. They easily aggregated as copper salts in the drying process of wet gel and decomposed into CuO particles in heating. While in the CuO/SiO₂ with the absence of PEO, the Cu was selectively entrapped as small particles in the gel skeleton due to the interaction between Cu aqua complex and silica gel network.     

Quantification of the pore size distribution (porosity profiles) in microfiltration membranes by SEM,TEM and computer image analysis

Transport properties of membranes are closely related to morphological properties like surface porosity and variation of their inner pore structure. Scanning electron microscopy (SEM) as well as transmission electron microscopy (TEM) are powerful tools to characterise the microscopical pore structure of membranes in a qualitative manner. In order to provide more quantitative data of surface and cross-sectional pores computer image analysis can be used. Parameters like ‘porous area fraction’ and ‘mean free path length’ have been selected to describe the pore distribution within porosity profiles in order to consider the effect that the pores within the cross-section are connected to each other.     

On the stability and properties of the polyacrylate/Na-MMT nanocomposite obtained by seeded emulsion polymerization

For high performance waterborne coatings usually polymer latexes with low emulsifier content are more preferred. Although polymer/clay nanocomposites offer improved properties, it is difficult to produce clay based nanocomposite latexes containing low emulsifier due to the stabilization problems especially caused by organoclays. Present study deals with the preparation of a tBA/BA/MAA ternary copolymer/clay nanocomposite containing 3 wt.% sodium montmorillonite (Na⁺-MMT) via seeded emulsion polymerization. Experimentally it was observed that even the usage of hydrophilic clay caused stabilization problem and a certain amount of emulsifier (>1 wt.%) was necessary to obtain stable latexes. In addition, the usage of a low molecular weight water soluble polymer as steric barrier was found to increase the stability of system. Obtained nanocomposite latex showed fine particle size diameter (127 nm) and very narrow size distribution (PDI = 0.06). The WAXD and TEM investigations indicated that a mostly exfoliated nanocomposite was obtained. Thermal analyses (DSC, DMTA and TGA) showed that there was no change at T_g of the copolymer while very high improvement was obtained for elastic modulus and a slight increase in thermal stability. According to the rheological measurements, the nanocomposite latex showed a higher low shear viscosity, a stronger shear thinning behavior and an improved physical stability in comparison to the reference latex.     

Fabrication and photoconductivity study of copper phthalocyanine/perylene composite with bulk heterojunctions obtained by solution blending

Copper tetra-(octyl-alkoxy-carbonyl)-phthalocyanine (CuPc-C8) and 3,4,9,10-tetra-(octyl-alkoxy-carbonyl)-perylene (Pery-C8) attached with long alkyl chains by covalent bonds were synthesized. Both of the two compounds showed good solubility in organic solvents, and the compatibility between them was improved. The novel composite of CuPc-C8/Pery-C8 was prepared by the solution-blending method. Atomic force microscopy (AFM) demonstrated the formation of the bulk heterojunction structure in their cast-coated films. Enhanced photosensitivity was observed in the photoreceptor made from the CuPc-C8/Pery-C8 composite, which was interpreted in terms of the large interfacial area between the two components due to the existence of the bulk heterojunction structure.     

Synthesis of homopolymers and multiblock copolymers by the living ring‐opening metathesis polymerization of norbornenes containing acetyl‐protected carbohydrates with well‐defined ruthenium and molybdenum initiators

The ring‐opening metathesis polymerization (ROMP) of norbornenes containing acetyl‐protected glucose [2,3,4,6‐tetra‐O‐acetyl‐glucos‐1‐O‐yl 5‐norbornene‐2‐carboxylate ( 1 )] and maltose [2,3,6,2′,3′,4′,6′‐hepta‐O‐acetyl‐maltos‐1‐O‐yl 5‐norbornene‐2‐carboxylate ( 2 )] was explored in the presence of Mo(N‐2,6‐ⁱPr₂C₆H₃)(CHCMe₂Ph)(O^tBu)₂ ( A ), Ru(CHPh)(Cl)₂(PCy₃)₂ ( B ; Cy = cyclohexyl), and Ru(CHPh)(Cl)₂(IMesH₂)(PCy₃) ( C ; IMesH₂ = 1,3‐dimesityl‐4,5‐dihydromidazol‐2‐ylidene). The polymerizations promoted by B and A proceeded in a living fashion with exclusive initiation efficiency, and the resultant polymers possessed number‐average molecular weights that were very close to those calculated on the basis of the monomer/initiator molar ratios and narrow molecular weight distributions (weight‐average molecular weight/number‐average molecular weight < 1.18) in all cases. The observed catalytic activity of B was strongly dependent on both the initial monomer concentration and the solvent employed, whereas the polymerization initiated with A was completed efficiently even at low initial monomer concentrations. The polymerization with C also took place efficiently, and even the polymerization with 1000 equiv of 1 was completed within 2 h. First‐order relationships between the propagation rates and the monomer concentrations were observed for all the polymerization runs, and the estimated rate constants at 25 °C increased in the following order: A > C > B . On the basis of these results, we concluded that ROMP with A was more suitable than ROMP with B or C for the efficient and precise preparation of polymers containing carbohydrates. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4248–4265, 2004     

Synthesis and polymerization of styrene monomers bearing spiroorthoester structure and volume change during crosslinking by double ring‐opening of the pendant spiroorthoesters of the obtained polymers

Novel styrene monomers bearing a five or seven‐membered spiroorthoester structure (SOE5, SOE7) were synthesized and their radical polymerizations as well as volume change during crosslinking of the obtained polymers were investigated. SOE5 and SOE7 were prepared from 4‐vinylbenzyl glycidyl ether and γ‐butyrolactone or ε‐caprolactone using boron trifluoride diethyl ether complex as a catalyst, respectively. Radical polymerizations of these monomers using 2,2′‐azobisisobutyronitrile (AIBN) gave the corresponding styrene‐based polymers with keeping the spiroorthoester structures unchanged. These polymers could be transformed to networked polymers by heating with a sulfonium antimonate, a thermally latent cationic polymerization initiator. Copolymerization of SOE5 or SOE7 with styrene at various compositions was carried out to efficiently obtain the corresponding copolymers, respectively. These polymers and copolymers showed little volume shrinkage or slight volume expansion during the crosslinking. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1790–1795     

Carbon/metal nanotubes with tailored order and configuration by direct carbonization of inverse block copolymer micelles inside nanoporous alumina

Carbonaceous nanotubes decorated with metal nanoparticles were obtained by heating inverse block copolymer micelles loaded with metal precursors inside nanoporous alumina. Simple changes in the applied temperature profile allowed tailoring of the wall morphology of the nanotubes and the spatial arrangement of the metal nanoparticles.     

Formation of the pore structure of modifi ed wood by treatment with heat and water

The effect of the heat treatment and subsequent treatment with water on the pore structure formation in a solid product made of birch sawdust with the addition of phosphoric acid was studied. The relationships characterizing the effect of the modifier, temperature, and treatment with water on the properties of the porous carbon material prepared from wood were revealed.     

Synthesis of aldehydes and ketones by the dehydrogenation of alcohols in the presence of a Raney nickel/aluminium isopropoxide/alumina catalyst

The synthesis of aldehydes and ketones by the dehydrogenation of allylic and secondary alcohols using a Raney-Ni-Al(i-OPr)₃-Al₂O₃ catalyst without hydrogen acceptors is presented.     

Optically pure trans-2,3-disubstituted N-sulfinyl aziridines. Regio- and stereoselective opening mediated by the sulfinyl group

A new entry to optically pure trans-2,3-disubstituted N-sulfinyl aziridines starting from 1,2-aminosulfides, involving formation of a sulfonium salt intermediate followed by intramolecular nucleophilic attack by the sulfinamide nitrogen atom, is reported. The regio- and stereoselective opening of the aziridine ring can be achieved by anchimeric assistance of the sulfinyl group.     

Resolution enhanced Ni Kα and Kβ spectra obtained by the deconvolution method

Ni K_α, and K_β spectra of NiO, NiF₂, and NiS were measured using a vacuum two-crystal high resolution X-ray spectrometer. In order to make clear fine structures due to multiplet splitting, numerical deconvolution with the lifetime broadening factor as a deconvoluting function was carried out in the frequency domain using a successive pseudo-deconvolution technique. Based on extensive simulation studies, the most appropriate polynomial smoothing function was chosen from among those given by Savitzky and Golay [Anal. Chem.36. 1627 (1964)]. The quartic 17-point and 11-point smoothing convolute functions were used for processing observed K_β and K_α spectra. Results obtained by a simple jj-coupling model including exchange interactions between two incomplete shells do not seem to be consistent with the deconvolution results.