Cylindrical Pores Of Uniform Diameter Research Articles

Hydrogen Bonding of Water Confined in Controlled-Pore Glass 10-75 Studied by 1H-Solid State NMR

The adsorption of water in the mesoporous silica material with cylindrical pores of uniform diameter, Controlled Pore Glass 10-75 (CPG), was studied by 1H-MAS solid state NMR spectroscopy. From the NMR spectra it is evident that inside the mesopores of the silica different water environments exist, which are characterized by their individual chemical shift. All observed hydrogen atoms are either surface –SiOH groups or hydrogen bonded water molecules. It is found that there exist some stronger bound water molecules on the surface which are not removable even by heating at a vacuum pump. As a tentative assignment these water molecules are attributed to surface defects or inaccessible cavities in the CPG 10-75. At intermediate water filling levels, the principal signal is a single NMR line with continuously varying chemical shift. This finding is interpreted as the result of a radial water filling mechanism. That is, the filling of the pore grows from the pore surface towards the pore axis. Finally it is shown that water is a sensor for surface and structural inhomogeneity and that a coexistence of inner pore and outer bulk water exists in the system.

Encapsulation of enzymes in alumina membranes of controlled pore size

Nanoporous Al 2O 3 membranes are employed in the development of amperometric biosensors for the immobilization of the biologically active elements. Anodized alumina membranes with the desired dimensions were prepared by controlled anodization of high purity aluminium in an acidic solution that slowly dissolves the formed aluminium oxide. The anodizing voltage controls the pore size and pore density, whereas the thickness is determined by the amount of transferred charge. This technique originates in the membrane an asymmetric structure of cylindrical pores of uniform diameter arranged in a hexagonal array perpendicular to the membrane surface. Such structure allows the uptake of relatively higher amounts of glucose oxidase (GO x) enzyme in a thin film. The preparation of the active phase of the biosensors is completed by procuring an external coating to the membrane surface with a natural polysaccharide, chitosan, which avoids the GO x leaching and provides a cage of high surface area inside the pores where the entrapped enzyme remains active. The aim of this study is to evaluate the influence of membrane dimensions on the biosensor response.

Hydrogen bonding of water confined in mesoporous silica MCM-41 and SBA-15 studied by 1H solid-state NMR.

The adsorption of water in two mesoporous silica materials with cylindrical pores of uniform diameter, MCM-41 and SBA-15, was studied by 1H MAS (MAS=magic angle spinning) and static solid-state NMR spectroscopy. All observed hydrogen atoms are either surface -SiOH groups or hydrogen-bonded water molecules. Unlike MCM-41, some strongly bound water molecules exist at the inner surfaces of SBA-15 that are assigned to surface defects. At higher filling levels, a further difference between MCM-41 and SBA-15 is observed. Water molecules in MCM-41 exhibit a bimodal line distribution of chemical shifts, with one peak at the position of inner-bulk water, and the second peak at the position of water molecules in fast exchange with surface -SiOH groups. In SBA-15, a single line is observed that shifts continuously as the pore filling is increased. This result is attributed to a different pore-filling mechanism for the two silica materials. In MCM-41, due to its small pore diameter (3.3 nm), pore filling by pore condensation (axial-pore-filling mode) occurs at a low relative pressure, corresponding roughly to a single adsorbed monolayer. For SBA-15, owing to its larger pore diameter (8 nm), a gradual increase in the thickness of the adsorbed layer (radial-pore-filling mode) prevails until pore condensation takes place at a higher level of pore filling.

Large scale copper microstructures generation using electro-deposition through nuclear track filters

Microstructure fabrication is not only of immense importance for microelectronics technology but also plays a vital role as a potent tool for carrying out investigations relating to behavior of materials at sub micron scales. In the recent years, it has broadened to encompass more and more areas of multidiscipline. A variety of possible applications include high power microwave generation, ultra fast computer and tetra hertz amplifier devices fabrication, radiation and temperature insensitive electronics. Fields where well-established applications already exist include field emitters; electrochemistry; conductive polymer nanofibers fabrication; transparent metal structures and macroscopic quantum tunneling phenomena. Of the many possible geometrical shapes and growth patterns, the simplest structure is probably an ensemble of wires. A variety of techniques like optical, X-rays, electron and ion beam lithography have been used for fabrication of such ensembles. However, electrochemical methods involving electrodeposition of metals into the etched pores of nuclear track filters (NTFs) of mica and polymers, are a convenient and simple technique [1–6]. The morphological study of such structures produced through electrochemical methods and of replicas of etched tracks in NTFs used as templates, has two-fold purpose. One, it provides the finest and critical details of the geometry and dimensions of microstructural constituent elements and the second, as a by product it enables to study the various aspects of interaction of a nuclear particle with given material leading to formation of tracks in NTF. It is well known that parameters, which control the shapes of tracks in NTFs, include the nature of the material; the ion beam and energy deposition rate; pre, post-irradiation storage and environment and the etching conditions. In the present work nuclear track filters of Makrofol (KG) polycarbonate having pore size ca. 2.6 μm and pore density 1 × 106 cm−2 have been used as templates for synthesis of copper microstructures using the technique of electrodeposition (template synthesis). Because the membranes used contain cylindrical pores of uniform diameter, crops of monodisperse microstructures of the desired material, whose dimensions can be carefully controlled, are obtained. Track etch membranes in the form of nuclear track filters have emerged as a spin-off from solid state nuclear track detectors (SSNTDs)-solid dielectric materials capable of storing tracks of energetic, heavily ionizing ions which can subsequently chemically amplified for optical observations as pores or channels of well defined geometry and pore density [3–6]. The size and dimensions of the pore depend upon various factors, viz. the nature and energy of the incident ions, the target material, etch conditions e.g., temperature, nature of the etchant. The pore size which is controllable, may range from few nm to mm. NTFs have been put to numerous applications besides their use in the synthesis of nano/microstructures. The underlying principle of template synthesis technique is akin to that of producing components through the use of replication e.g., die-casting or mold casting, like making ice candies out of molds. In this technique, materials can be deposited with in the template membranes by either electrochemical or chemical (electroless) reduction of the appropriate metal ion. The generated structures can both be homogeneous or heterogeneous depending on the pore size and geometries, with complete control over the aspect ratio (length and diameter ratio). The simple and well known underlying concept of electrodeposition of metals through electroplating is described as an electrochemical process in which metallic ions in a supporting solution are reduced to the metallic state at the cathode, which is closely covered by an NTF membrane, would lead to formation of growth of plated film as the embodiment of micro or nano structure. The etched pores of the membranes would act as templates [1–10]. Electrodeposition (template synthesis) is a versatile technique combining low processing cost with ambient conditions that can be used to prepare metallic, polymeric and semi conducting microstructures. In the case of microstructures arrays, electro deposition is the cost effective method with which such structures have been successfully fabricated. Samples of polycarbonate of thickness 30 μm were irradiated to 13.64 MeV/n 238U ions (fluence 106 ions/cm2)utilizing the heavy ion accelerator UNILAC facility at GSI, Darmstadt, Germany. Samples were etched in 6N NaOH solution at 70 ◦C for 40 min and pore size of 2.6 μm was obtained. After etching nuclear track filter having pore size 2.6 μm and pore density 106/cm2 is used for synthesis of iron microstructures using the technique of electrodeposition. Because the membranes used contain cylindrical pores of uniform diameter, crops of

Preparation of PPV Nanotubes and Nanorods and Carbonized Products Derived Therefrom

We report the synthesis of poly(p-phenylene vinylene) (PPV), a polyconjugated polymer, in nanotube and nanorod shapes, and carbonized products derived therefrom. PPV tubes and rods could be prepared on the inner surface of or inside the nanopores (10−200 nm diameter) in alumina or polycarbonate membrane filters by the chemical vapor deposition (CVD) polymerization method of α,α‘-dichloro-p-xylene followed by thermal dehydrochlorination. The PPV nanotubes and nanorods thus obtained could be converted to the corresponding carbonized tubes and nanorods when they were subjected to thermal treatment under an argon atmosphere. Thus prepared nanoobjects were characterized by electron microscopic analyses, IR, UV−vis, and Raman spectroscopy, and photoluminescence fluorometry. This investigation demonstrates that, if one employs membrane filters containing cylindrical pores of uniform diameter, monodisperse nanotubes and nanorods of PPV and carbonized products thereof with controlled diameter and wall thickness ca...

Membrane-Based Synthesis of Nanomaterials

This paper reviews a relatively new method for preparing nanomaterials: membrane-based synthesis. This method entails the synthesis of the desired material within the pores of a nanoporous membrane. Because the membranes employed contain cylindrical pores of uniform diameter, monodisperse nanocylinders of the desired material, whose dimensions can be carefully controlled, are obtained. These nanocylinders may be either hollow (a tubule) or solid (a fibril or nanowire). We call this approach the “template” method because the pores in the nanoporous membranes are used as templates for forming the desired material. This template method is a very general approach; it has been used to prepare nanotubules and fibrils of polymers, metals, semiconductors, carbons, and other materials.

Template synthesis of graphitic nanotubules*

Ensembles of graphite‐based nanotubes (see Fig.) have been produced by extending a template approach successfully used for metals and semiconductors to carbons. The outer andinner diameters of the tubules can be controlled by varying the time allowed for the polymerization of acrylonitrile within the pores of a nanotubes formed in the pores are subsequently graphitized at high temperatures to form the graphitized nanotubes magnified image.

Bioactive Void Metal Composites for Orthopedic Implant Devices

AbstractAlthough significant advances have been made to provide mechanically strong and nontoxic metals and alloys, biological integration of devices into natural tissues remains a problem. The Surface Induced Mineralization (SIM) and Void Metal Composite (VMC) processes produce a bioactive porous metal implant coating/device which may address many of the problems associated with conventional processing methods.The VMC process produces materials which have cylindrical pores of uniform diameter which can completely penetrate the structure of the material. The pore diameter, orientation and interconnectivety are easily controlledThe SIM process uses the idea of nature's template-mediated mineralization by chemically modifying the implant to produce a surface which induces heterogeneous nucleation from aqueous solution. SIM produced bioactive coatings provide 1) control of the thickness and density of the mineral phase, 2) a way to coat porous metals, complex shapes and large objects, 3) the ability to coat a wide variety of materials, 4) potential choice for the phase of the mineral formed.

Nanomaterials: A Membrane-Based Synthetic Approach

Materials with nanoscopic dimensions not only have potential technological applications in areas such as device technology and drug delivery but also are of fundamental interest in that the properties of a material can change in this regime of transition between the bulk and molecular scales. In this article, a relatively new method for preparing nanomaterials, membrane-based synthesis, is reviewed. This method entails synthesis of the desired material within the pores of a nanoporous membrane. Because the membranes used contain cylindrical pores of uniform diameter, monodisperse nanocylinders of the desired material, whose dimensions can be carefully controlled, are obtained. This "template" method has been used to prepare polymers, metals, semiconductors, and other materials on a nanoscopic scale.

Design of pores in alumina

Various procedures are suggested for obtaining alumina foils containing parallel cylindrical pores of uniform diameter over the size range of 1.5–20 nm. Pores larger than 6 nm are obtained by anodizing aluminum foils in solutions of sulfuric acid at low temperatures and subsequently etching them in a phosphoric acid solution. Smaller pores are obtained by anodizing 30–60-nm-thick aluminum films at low temperatures in a dilute sulfuric acid bath or in a bath containing a mixture of sulfuric and tartaric acids.

Studies on pore systems in catalysts: IX. Calculation of pore distributions from the adsorption branch of nitrogen sorption isotherms in the case of open cylindrical pores A. Fundamental equations

A study is made of the possible cause for sorption hysteresis in the case of cylindrical pores of uniform diameter, open at both ends. By means of simple thermodynamic reasoning, the equation of Cohan for capillary condensation in open cylinders during adsorption, is shown not to be suitable for quantitative work. After the introduction of the t curve of multimolecular adsorption, a model is given for the occurrence of hysteresis in this special case. From this model, quantitative relations are derived for the spontaneous filling of pores during adsorption, as well as for the evaporation of capillary condensate on desorption, in dependence of the pore radius. The relation between these equations and the work of Foster and Derjaquin is discussed.