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We report gas and liquid transport measurements through membranes that have 40% voids made of 14 nm pores. A reactive polylactide-polynorbornenylethylstyrene block polymer is used as a structural template in the polymerization of dicyclopentadiene during the membrane formation process. After the membrane is cast, the pore structure is formed by etching the polylactide component using dilute aqueous base. The pore structure is isotropic; therefore, there is no need for special alignment techniques. Knudsen diffusion experiments and water flow experiments show pores with a tortuosity of 1.81 and a size of 14 nm, a diameter consistent with nitrogen adsorption and small-angle X-ray scattering measurements. These membranes are effective for ultrafiltration, with molecular weight cutoffs (MWCO) consistent with theoretical predictions with no adjustable parameters. These MWCO's can be tuned by changing the size of the constituent blocks in the templating copolymer.
ACS Appl Mater Interfaces 2009 Feb
PMID:Diffusion and flow across nanoporous polydicyclopentadiene-based membranes. 2035 39

Nine non-noble-metal catalysts (NNMCs) from five different laboratories were investigated for the catalysis of O(2) electroreduction in an acidic medium. The catalyst precursors were synthesized by wet impregnation, planetary ball milling, a foaming-agent technique, or a templating method. All catalyst precursors were subjected to one or more heat treatments at 700-1050 degrees C in an inert or reactive atmosphere. These catalysts underwent an identical set of electrochemical characterizations, including rotating-disk-electrode and polymer-electrolyte membrane fuel cell (PEMFC) tests and voltammetry under N(2). Ex situ characterization was comprised of X-ray photoelectron spectroscopy, neutron activation analysis, scanning electron microscopy, and N(2) adsorption and its analysis with an advanced model for carbonaceous powders. In PEMFC, several NNMCs display mass activities of 10-20 A g(-1) at 0.8 V versus a reversible hydrogen electrode, and one shows 80 A g(-1). The latter value corresponds to a volumetric activity of 19 A cm(-3) under reference conditions and represents one-seventh of the target defined by the U.S. Department of Energy for 2010 (130 A cm(-3)). The activity of all NNMCs is mainly governed by the microporous surface area, and active sites seem to be hosted in pore sizes of 5-15 A. The nitrogen and metal (iron or cobalt) seem to be present in sufficient amounts in the NNMCs and do not limit activity. The paper discusses probable directions for synthesizing more active NNMCs. This could be achieved through multiple pyrolysis steps, ball-milling steps, and control of the powder morphology by the addition of foaming agents and/or sulfur.
ACS Appl Mater Interfaces 2009 Aug
PMID:Cross-laboratory experimental study of non-noble-metal electrocatalysts for the oxygen reduction reaction. 2035 76

In this work, we synthesized chiral mesoporous silica (CMS) spheres, which can be used as a potential candidate for chiral separation. The CMS spheres with controllable pore sizes (of 2-3 nm) and high surface areas of ca. 614 m(2) g(-1) were synthesized by chiral templating with chiral block copolymers based on poly(ethylene oxide) and dl-glutamic acid [PEO(113)-b-(GluA)(10)]. The ordered structure of the chiral mesopores was characterized by high-resolution transmission electron microscopy, and the average pore diameters of chiral mesopores were estimated from the nitrogen adsorption-desorption measurements. The enantioselectivity properties and chiral resolution kinetics of the mesopores of silica spheres, after extraction of chiral polymers of PEO(113)-b-(l/d-GluA)(10), were scrutinized using a racemic solution of valine and measuring the circular dichroism and optical polarimetery. A chiral selectivity factor of 5.22 was found with a specific enantiomer of valine adsorbed preferably. These results raise the new possibilities of CMS spheres for enantiomeric separation and other enantioselective applications.
ACS Appl Mater Interfaces 2009 Aug
PMID:Enantioselective separation using chiral mesoporous spherical silica prepared by templating of chiral block copolymers. 2035 1

Three new fused-ring pyrazine derivatives end-functionalized with trifluoromethylphenyl groups have been synthesized. The effect of a fused-ring pyrazine core on the thermal, electronic, optical, thin film morphology, and organic field-effect transistor (OFET) properties was investigated both experimentally and theoretically. Electrochemistry measurements and density functional theory calculations suggest that the pyrazine core plays a significant role in tuning the electron affinities of these compounds. The optical absorption and fluorescence properties are also sensitive to the pyrazine core. The OFET devices based on the fused-ring pyrazine compounds exhibit electron mobilities as high as ca. 0.03 cm(2) V(-1) s(-1) under nitrogen, and their performance is sensitive to the pyrazine core. The larger pyrazine core leads to a lower LUMO level and lower reorganization energy, to more ordered thin film morphology with larger grain size, and finally to higher mobilities.
ACS Appl Mater Interfaces 2009 May
PMID:Fused-ring pyrazine derivatives for n-type field-effect transistors. 2035

Indium-tin-oxynitride (ITON) films have been fabricated by rf sputtering from an indium-tin-oxide target in nitrogen plasma. The influence of postdeposition annealing up to 800 degrees C is analyzed by electrical, optical, and surface characterization of the films in comparison to indium-tin-oxide (ITO) films fabricated in argon plasma. High-temperature annealing resulted in ITO(N) films with similar carrier concentrations. However, the resistivity and optical transmittance of the ITON films were higher than those of the ITO films. Photoelectron spectroscopy revealed that nitrogen is incorporated into the ITON structure in an unbound state as well as through the formation of metal-nitrogen and oxynitride bonds that decorate oxygen vacancies. When the core level electron spectra of ITO and ITON films are compared, a correlation between carrier concentration and the incorporated nitrogen is found. Changes in ITON electrical properties are mainly induced by the release of nitrogen at temperatures above 550 degrees C. In this context, ohmic contact behavior was achieved for ITON on p-type GaN after annealing at 600 degrees C, while no ohmic contact could be realized using ITO.
ACS Appl Mater Interfaces 2009 Jul
PMID:Effect of annealing on the properties of indium-tin-oxynitride films as ohmic contacts for gan-based optoelectronic devices. 2035 48

Reflective and surface conductive polyimide films were prepared by the incorporation of silver(I) acetate and trifluoroacetylacetone into a dimethylacetamide solution of the poly(amic acid) formed 3,3',4,4'-oxidiphthalic dianhydride (ODPA) and 4,4'-oxidianiline (4,4'-ODA). Thermal curing of (trifluoroacetylacetonato)silver(I)-poly(amic acid) films led to cycloimidization with concomitant silver(I) reduction, which yielded a reflective and conductive silver surface at selected silver concentrations if the film was cured to a final temperature of 300 degrees C for several hours. The metallized ODPA/4,4'-ODA films retain the essential mechanical properties of an undoped film and have good thermal stability, particularly under a nitrogen atmosphere. The bulk of the composite film was not electrically conductive. The use of (hexafluoroacetylacetonato)silver(I) and silver(I) tetrafluoroborate as sources of silver(I) with ODPA/4,4'-ODA yielded modestly reflective films that never developed conductivity. The silvered films prepared with (trifluoroacetylacetonato)silver(I) can be patterned using mask-etch techniques. Comparisons are made among four similar silver-polyimide systems, with the polyimides being ODPA/4,4'-ODA, BTDA/4,4'-ODA, BPDA/4,4'-ODA, and 6FDA/4-BDAF.
ACS Appl Mater Interfaces 2009 Jul
PMID:Single-stage synthesis and characterization of reflective and conductive silver-polyimide films prepared from silver(I) complexes with ODPA/4,4'-ODA. 2035 49

Chlorophyll (Chl) was immobilized into a 1,4-butanediol-modified MCM-41 (BMCM-41) intercalated by poly(3-hexylthiophene) (P3HT) to form BMCM-41/P3HT/Chl nanocomposites having P3HT contents of 10, 30, 60, and 90 wt % from a solution-casting method. Wide-angle X-ray diffraction and transmission electron microscopy studies indicate that the pore structure of MCM-41 was retained after surface modification and a subsequent P3HT intercalation process. Scanning electron microscopy images showed that the BMCM-41 nanoparticles dispersed into the polymer matrix of BMCM-41/P3HT/Chl, and the sample with 10 wt % P3HT content gives the most homogeneous nanoparticle dispersion. Nitrogen adsorption-desorption results confirmed that the P3HT intercalation and Chl immobilization inside the BMCM-41 mesopore were successfully carried out. The pore volume and surface area of BMCM-41 decreased significantly when the amount of P3HT was increased from 10 to 90 wt %. The UV-vis study showed a blue shift of the pi-pi* transition band of P3HT in the spectra of BMCM-41/P3HT/Chl nanocomposites. The FT-IR study indicates an increase of the thiophene ring stretching and a decrease of the C horizontal lineO stretching when P3HT and Chl were inside the mesopore. The photovoltaic property of Chl-doped P3HT was improved significantly upon the addition of BMCM-41 nanoparticles, and BMCM-41/P3HT-10/Chl exhibits the highest incident photon-to-current conversion efficiency of 7.16%.
ACS Appl Mater Interfaces 2009 Jul
PMID:Molecular aggregation state and photovoltaic properties of chlorophyll-doped conducting poly(3-hexylthiophene)/MCM-41 nanocomposites. 2035 59

We report the fabrication and ultrafiltration performances of an asymmetric composite membrane with a mesoporous TiO2 skin layer coated on a macroporous alumina support. Mesoporous TiO2 was first prepared and deposited on the substrate through a sol-gel process where a ethylene oxide and propylene oxide triblock polymer (PEO-PPO-PEO, P123) was used to modify the properties of the sols and also to introduce assembled pores in the skin layer. The obtained mesoporous TiO2 membrane was characterized by means of scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and nitrogen adsorption. We found that there were two types of wormlike mesopores present in the TiO2 membrane: interparticle and assembled pores. By carefully controlling the sol properties, we made the two types of pores match each other, which means the size of the interparticle pores is close or smaller than that of the assembled pores. This pore-size matching ensures a narrow pore-size distribution and, consequently, a good retention performance of the obtained TiO2 membrane. The pore size of the TiO2 membrane is ca. 6 nm, as revealed by both nitrogen adsorption and dextran separation experiments, and it has a pure water flux of 7.12 L/(m(2) x h x bar) and a cutoff molecular weight of 19 000 Da, which is very attractive for applications in the enrichment and separation of proteins and polypeptides.
ACS Appl Mater Interfaces 2009 Jul
PMID:Fabrication of supported mesoporous TiO2 membranes: matching the assembled and interparticle pores for an improved ultrafiltration performance. 2035 68

To improve the biocorrosion resistance of stainless steel (SS) and to confer the bactericidal function on its surface for inhibiting bacterial adhesion and biofilm formation, well-defined inorganic-organic hybrid coatings, consisting of the inner compact titanium oxide multilayers and outer dense poly(vinyl-N-hexylpyridinium) brushes, were successfully developed. Nanostructured titanium oxide multilayer coatings were first built up on the SS substrates via the layer-by-layer sol-gel deposition process. The trichlorosilane coupling agent, containing the alkyl halide atom-transfer-radical polymerization (ATRP) initiator, was subsequently immobilized on the titanium oxide coatings for surface-initiated ATRP of 4-vinylpyridine (4VP). The pyridium nitrogen moieties of the covalently immobilized 4VP polymer, or P(4VP), brushes were quaternized with hexyl bromide to produce a high concentration of quaternary ammonium salt on the SS surfaces. The excellent antibacterial efficiency of the grafted polycations, poly(vinyl-N-pyridinium bromide), was revealed by viable cell counts and atomic force microscopy images of the surface. The effectiveness of the hybrid coatings in corrosion protection was verified by the Tafel plot and electrochemical impedance spectroscopy measurements.
ACS Appl Mater Interfaces 2009 Mar
PMID:Inorganic-organic hybrid coatings on stainless steel by layer-by-layer deposition and surface-initiated atom-transfer-radical polymerization for combating biocorrosion. 2035 86

Dialkyldithiophosphates (DTPs) of zinc(II), copper(II), and other metals have been extensively used as multifunctional additives in lubricants to control friction and reduce wear in mechanical systems. Among these DTP compounds, zinc dialkyldithiophosphates (ZnDTPs) are the most common additives extensively used for more than 60 years. These additives form a protective film on steel surfaces and, thus, control friction and reduce wear. However, ZnDTPs contain zinc and large amounts of phosphorus and sulfur, which impair the environment, both directly and indirectly, by adversely affecting the performance of catalytic converters of various automobiles. For this reason, environmental legislation imposes limitations on concentrations of phosphorus, sulfur, and zinc in the lubricants. In this work, we report on zinc-free S-di-n-octoxyboron-O,O'-di-n-octyldithiophosphate (DOB-DTP) lubricant additive with amount of phosphorus and sulfur reduced by half in a molecule as compared with ZnDTPs. DOB-DTP was synthesized by a reaction in two steps under inert nitrogen atmosphere. The final product, a viscous liquid, was characterized by the elemental analysis, FT-IR, multinuclear (1)H, (13)C, (31)P, and (11)B NMR spectroscopy and thermal analyses. Tribological performance of a mineral oil with this new additive was evaluated in comparison with O,O'-di-n-butyl-dithiophosphato-zinc(II) (ZnDTP) using a four-ball tribometer. The surface morphology and the elemental composition of the tribofilms were characterized using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS). The results show that DOB-DTP has a considerably better antiwear performance and higher stability of the coefficient of friction with time as compared with ZnDTP. Both phosphorus and sulfur were detected by the EDS on the worn steel surfaces at all concentrations of additives in the base oil.
ACS Appl Mater Interfaces 2009 Dec
PMID:Synthesis, physicochemical, and tribological characterization of S-Di-n-octoxyboron-O,O'-di-n-octyldithiophosphate. 2035 64


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