Porous anodic alumina membranes with Y-branched and double-branched nanopores were fabricated by the stepwise reduction of anodizing potential during the second step of anodization carried out in 0.3 M oxalic acid. The process of nanoporous layer formation and influence of anodizing parameters on structural features of as-obtained anodic aluminum oxide (AAO) membranes were discussed in detail. The pore rearrangement process occurring after the potential decrease was investigated on the basis of the current density vs. time curves, and results were correlated with the field-emission scanning electron microscope images of the pore bottoms taken after different anodizing durations. It was found that the reorganization of nanopores begins after 600 and 500 s from the time of the potential reduction to 42 and 30 V and the process seems to be completed after about 900 and 800 s, respectively. The through-hole AAO membranes were used as templates for the fabrication of gold and polystyrene nanowires via electrochemical deposition and simple immersing in the polymer solution, respectively. The arrays of hierarchically branched nanowires were synthesized, and the dimensions of nanowires were consistent with the shape and structure of used AAO templates.
As an important property of porous membranes, the surface charge property determines many ionic behaviors of nanopores, such as ionic conductance and selectivity. Based on the dependence of electric double layers on bulk concentrations, ionic conductance through nanopores at high and low concentrations is governed by the bulk conductance and surface charge density, respectively. Here, through the investigation of ionic conductance inside track-etched single polyethylene terephthalate (PET) nanopores under various concentrations, the surface charge density of PET membranes is extracted as ∼−0.021 C/m2 at pH 10 over measurements with 40 PET nanopores. Simulations show that surface roughness can cause underestimation in surface charge density due to the inhibited electroosmotic flow. Then, the averaged pore size and porosity of track-etched multipore PET membranes are characterized by the developed ionic conductance method. Through coupled theoretical predictions in ionic conductance under high and low concentrations, the averaged pore size and porosity of porous membranes can be obtained simultaneously. Our method provides a simple and precise way to characterize the pore size and porosity of multipore membranes, especially for those with sub-100 nm pores and low porosities. 相似文献
Solid‐state nanopores are nanoscale channels through otherwise impermeable membranes. Single molecules or particles can be passed through electrolyte‐filled nanopores by, e.g. electrophoresis, and then detected through the resulting physical displacement of ions within the nanopore. Nanopore size, shape, and surface chemistry must be carefully controlled, and on extremely challenging <10 nm‐length scales. We previously developed a framework to characterize nanopores from the time‐dependent changes in their conductance as they are being formed through solution‐phase nanofabrication processes with the appeal of ease and accessibility. We revisited this simulation work, confirmed the suitability of the basic conductance equation using the results of time‐dependent experimental conductance measurements during nanopore fabrication by Yanagi et al., and then deliberately relaxed the model constraints to allow for (i) the presence of defects; and (ii) the formation of two small pores instead of one larger one. Our simulations demonstrated that the time‐dependent conductance formalism supports the detection and characterization of defects, as well as the determination of pore number, but with implementation performance depending on the measurement context and results. In some cases, the ability to discriminate numerically between the correct and incorrect nanopore profiles was slight, but with accompanying differences in candidate nanopore dimensions that could yield to post‐fabrication conductance profiling, or be used as convenient uncertainty bounds. Time‐dependent nanopore conductance thus offers insight into nanopore structure and function, even in the presence of fabrication defects. 相似文献
The self‐assembly of block copolymers is an emerging strategy to produce isoporous ultrafiltration membranes. However, thus far, it has not been possible to bridge the gap from ultra‐ to nanofiltration and decrease the pore size of self‐assembled block copolymer membranes to below 5 nm without post‐treatment. It is now reported that the self‐assembly of blends of two chemically interacting copolymers can lead to highly porous membranes with pore diameters as small as 1.5 nm. The membrane containing an ultraporous, 60 nm thin separation layer can fully reject solutes with molecular weights of 600 g mol?1 in aqueous solutions with a water flux that is more than one order of magnitude higher than the permeance of commercial nanofiltration membranes. Simulations of the membrane formation process by dissipative particle dynamics (DPD) were used to explain the dramatic observed pore size reduction combined with an increase in water flux. 相似文献
The combination of nonsolvent‐induced phase separation and the self‐assembly of block copolymers can lead to asymmetric membranes with a thin highly ordered isoporous skin layer. The effective pore size of such membranes is usually larger than 15 nm. We reduced the pore size of these membranes by electroless gold deposition. We demonstrate that the pore sizes can be controlled precisely between 3 and 20 nm leading to a tunable sharp size discrimination in filtration processes. Besides fractionation of nanoparticles and biomaterials, controlled drug delivery is an attractive potential application. 相似文献
In this work, we address the capability of glow discharge optical emission spectroscopy (GDOES) for fast and accurate depth profiling of multilayer nitride coatings down to the nanometer range. This is shown by resolving the particular case of CrN/AlN structures with individual thickness ranging from hundreds to few nanometers. In order to discriminate and identify artefacts in the GDOES depth profile due to the sputtering process, the layered structures were verified by Rutherford backscattering spectrometry (RBS) and scanning electron microscopy (SEM). The interfaces in the GDOES profiles for CrN/AlN structures are sharper than the ones measured for similar metal multilayers due to the lower sputtering rate of the nitrides. However, as a consequence of the crater shape, there is a linear degradation of the depth resolution with depth (approximately 40 nm/μm), saturating at a value of approximately half the thickness of the thinner layer. This limit is imposed by the simultaneous sputtering of consecutive layers. The ultimate GDOES depth resolution at the near surface region was estimated to be of 4–6 nm. 相似文献
Track-etched polymer membranes are used to realize low-voltage electroosmotic (EO) pumps. The nanopores in polycarbonate (PC) and polyethylene terephthalate (PET) membranes were fabricated by the track-etching technique, the pore diameter was controlled in the range of 100 to 250 nm by adjusting the etching time. The results show that these EO pumps can provide high flow rates at low applied voltages (2-5 V). The maximum normalized flow rate is as high as 0.12 ml min(-1) V(-1) cm(-2), which is comparable to the best values of previously demonstrated EO pumps. We attribute this high performance to the unique properties of the track-etched nanopores in the membranes. 相似文献
Electrodeposition of nanoparticles (NPs) is a promising route for the preparation of highly electroactive nanostructured electrodes. By taking advantage of progressive electrodeposition, disordered arrays with a wide size distribution of Ag NPs are produced. Combined with surface‐reaction monitoring by using highly sensitive backside absorbing‐layer optical microscopy (BALM), such arrays offer a platform for screening size‐dependent electrochemistry at the single NP level. In particular, this strategy allows rationalizing the electrodeposition dynamics at the single‐NP level (>10 nm), up to the point of quantifying the presence of metal nanoclusters (<2 nm), and probing easier NP oxidation with size decrease, either through electrochemical or galvanic reactions. 相似文献
Summary: Organic‐inorganic hybrid materials consisting of nanosized silica particles with surface grafted PS or PS‐b‐PMMA were synthesized using ATRP. These hybrid materials were used in the fabrication of highly‐ordered isoporous membranes. Optical characterization revealed that the membranes consisted of hexagonally ordered pores of uniform size. The combination of an open pore structure and high surface area makes isoporous membranes into materials of high interest in fields as biotechnology and photonics.
The development of new nonlinear optical (NLO) materials for deep‐ultraviolet (DUV) applications is in great demand. However, the synthesis of an ideal DUV NLO crystal is a serious challenge. Herein, three new alkali‐metal fluorooxoborates, AB4O6F (A=K, Rb, and Cs, and a mixed cation between two of them), were successfully synthesized by cation regulation. It is found that all reported compounds exhibit short UV absorption edges (<190 nm), and show second harmonic generation (SHG) responses ranging from 0.8 to 1.9 KH2PO4 (KDP). Interestingly, by judicious selection of the A‐site alkali‐metal cations, the arrangement of NLO‐active structural units is fine‐tuned to an optimal configuration, which contributes to large SHG responses. 相似文献
One of the most commonly employed detection methods in microfluidic research is fluorescence detection, due to its ease of integration and excellent sensitivity. Many analytes though do not show luminescence when excited in the visible light spectrum, require suitable dyes. Deep‐ultraviolet (UV) excitation (<300 nm) allows label‐free detection of a broader range of analytes but also mandates the use of expensive fused silica glass, which is transparent to UV light. Herein, we report the first application of label‐free deep UV fluorescence detection in non‐UV transparent full‐body polymer microfluidic devices. This was achieved by means of two‐photon excitation in the visible range (λex = 532 nm). Issues associated with the low optical transmittance of plastics in the UV range were successfully circumvented in this way. The technique was investigated by application to microchip electrophoresis of small aromatic compounds. Various polymers, such as poly(methyl methacrylate), cyclic olefin polymer, and copolymer as well as poly(dimethylsiloxane) were investigated and compared with respect to achievable LOD and ruggedness against photodamage. To demonstrate the applicability of the technique, the method was also applied to the determination of serotonin and tryptamine in fruit samples. 相似文献
An application of the “pore filling” concept yielded high‐performance composite membranes for the selective pervaporation (PV) separation of aromatic/non‐aromatic hydrocarbon mixtures. Asymmetric polyacrylonitrile (PAN) membranes (average pore size of about 12 nm) were used as support for polymeric PV separation phases which were prepared in situ by heterogeneous photo‐initiated graft copolymerization. The impact of chain length of methyl polyoxyethylene (meth)acrylates and preparation parameters (UV irradiation time and degree of grafting) were analysed using PV with toluene/heptane (20/80 wt‐ratio; 80°C) as model feed. High selectivity and high permeate fluxes were achieved. Major reasons for the excellent performance were the small effective PV barrier thickness (< 5μm) and the covalent anchoring of the coated polymer. 相似文献
Hyper‐cross‐linked resins stemming from a gel‐type poly‐chloromethylated poly(styrene‐co‐divinylbenzene) resin (GT) have been investigated by a multi‐methodological approach based on elemental analysis, scanning electron microscopy, X‐ray microanalysis, and solvent absorption. The hyper‐cross‐linking of the parent resin was accomplished by Friedel–Crafts alkylation of the phenyl rings of the resins with the chloromethyl groups. This produced a permanent pore system comprising both micropores (<2.0 nm in diameter) and mesopores (2.2 nm). The chloromethyl groups that did not react in the hyper‐cross‐linking step were transformed into methylmercaptan groups and the latter were then converted into sulfonic groups by oxidation with hydrogen peroxide. By this procedure the extensive permanent porosity of the parent unsulfonated hyper‐cross‐linked polymer (HGT) was retained by the sulfonated polymer (HGTS). The final exchange capacity of HGTS was determined to be 0.36 mmol g?1. HGTS was easily metalated with PdII and the subsequent reduction of the metal centers with either aqueous sodium borohydride, formaldehyde, or dihydrogen produced three Pd0/HGTS nanocomposites. The metal nanoparticles had diameters in the 1–6 nm range for all the nanocomposites, as determined by TEM, but with somewhat different distributions. When formaldehyde was used, more than 90 % of the nanoparticles were less than 3 nm and their radial distribution throughout the polymer beads was quite homogeneous. These findings show that with this reducing agent the metal nanoparticles are generated within the pore system of the polymer matrix, hence their size is controlled by the dimensions of the pores of the polymeric support. 相似文献