Channel track-etched

Many molecular dynamics simulations have focused on the electrolyte solution factors and ignored the atomic features of the pore wall. The assumptions of these simulations may match more closely the experiments of inorganic channels, such as track-etched nu-... 

The transport velocity of Li+ is faster than that of Na+ and K+ due to the size of the cation. The data are consistent with a hopping transport mechanism of the cations accompanied by a non-specific co-transport of the anions. The transport rates for N03 > Cl- > C104 are related to the adjacent hydrate shell and not yet fully understood. Anyway, a path in the center of the supramolecular tubes, where the crown ethers assemble, must exist and allow for the co-transport of the anions. By forming the membranes in the pores of track-etched membranes, the transport rates could be improved by an order of magnitude due to the orientation of the channels perpendicular to the membrane surface. 

The scope of applications of MF has been broadened in recent years by the introduction of inert membranes, particularly polypropylene, polycarbonate, and Teflon . In general, these materials cannot be made by the methods developed for the cellulosics because of their insolubility. Both Teflon and pol)propylene MF membranes have been made by a controlled stretching procedure in which microtears are introduced Microporous polycarbonate membranes have been prepared by a unique radiation-track-etch method A thin polycarbonate film is exposed to ionizing radiation which leaves labile sites that can later be chemically etched to produce straight-throi channels. The pore size can be controlled by the etching conditions. The pores in these membranes, contrary to those in cellulosic membranes, are quite uniform in diameter. 

Commercial track-etch polycarbonate membranes (Whatman Nuclepore , nominal channel diameter 0.1 pm) were used and investigated by means of... 

Straight channels - cylindrical, conical, (a)symmetric Anodic oxidation (alumina) track etch... 

The formation of nanostructured arrays of conjugated polymers by the utilization of nanoporous templates has been reported. The deposition of the polymer inside the pores can be achieved by filling the pores with a solution of polymer and evaporation of the solvent or by the direct synthesis of conjugated polymer inside the pores by chemical or electrochemical approaches. Porous templates were based on track-etched polycarbonate membranes [106-108] or alumina that is obtained by anodic aluminum oxidation (AAO) [109-lllj. Thus, periodic vertical channels with diameters between 20 and 120 nm are formed by first electrochemical oxidation and etching and then subsequent etching for pore widening (Figure 13.16). 

Template-based synthesis involves the fabrication of the desired material within the pores or channels of a nanoporous template. A template may be defined as a central structure within which a network forms in such a way that removal of the template creates a filled cavity with morphological and/or stereochemical features related to those of the template. Track-etch membranes, porous alumina, and other nanoporous structures have been characterized as templates. Electrochemical and electroless depositions, chemical polymerization, sol-gel deposition, and chemical vapor deposition have been presented as major template synthetic strategies. Template-based synthesis can be used to prepare nanostructures of conductive polymers, metals, metal oxides, semiconductors, carbons, and other solid matter... 

Similar to the retention of LLC phases, thermotropic LC assemblies have also been covalently captured, leading to robust polymer films that retain the original nanostructures. Mdller et al. cross-linked columnar assemblies formed by amphiphile 7 bearing crown ether units inside the pores of track-etched membranes and obtained membranes containing oriented channels. Salt-diffusion experiments demonstrated that the resultant nanoporous membrane displayed... 

Both acid anodized aluminum (alumite membrane) (141, 142) and nuclear track-etched membranes have been used as a template. The nuclear track-etched membranes are prepared by irradiation/chemical etching (143) and contain linear, cylindrical pores of nearly uniform pore diameter. This ensures that the holes in the template are circular and approximately of the same diameter. More recently, porous nano-channel glass (144), and etched wafers of micro-channel plate glass have served as templates (125). The advantage of using porous membranes as templates can be found in their function as arrays of microelectrodes. They exhibit small potential drops, which make the electrochemical measurements possible when... 

To prepare membranes with artificial nanochannels, one can start with several polymer materials such as polyimide (PI), polycarbonate (PC), and polyethylene terephthalate (PET). A prerequisite to apply these kinds of polymers for nanochannel fabrication is that they are easy to process and susceptible to different etching techniques to produce nano-sized channels of different morphologies. Current methods for this purpose include ion-track-etching, electrochemical etching, and laser techniques. Once the nanochannels have been produced, one needs to functionalize the channel inner wall to obtain different functions. Following are some examples of polymer decorated nanochannels. 

Electrodeposition into templates. A most often used approach to create aligned nanostructures (such as nanowires, -tubes and similar, perpendicular to the electrode) is deposition into a nanoporous template. Such templates may be - as illustrated in Fig. 1 - porous alumina, self-assembled polystyrene beads, ion track-etch channels. Both cathodic and anodic electrodeposition of structures can be achieved, such as metal oxides, sulfides, or tellurides, as well as polymers. " °°... 

Later, this ion channel mimicking concept was used to detect the binding events directly on an ISM by using a covalently biotinylated membrane surface. The binding of avidin in this case directly hindered the electrochemically imposed ion transfer kinetics of sodium ion, and subsequently decreased the super-Nernstian step that is characteristic of a surface depletion of the marker ion. To enhance the sensitivity, which depends on the fraction of the surface blocked by avidin, the active surface area was reduced by applying a hydrophilic track-etch nanopore membrane on top of the biotinylated ISM surface. ... 

Another method of template-assisted synthesis, mainly used for the growth of metal nanowires, involves the deposition of metal into the cyUndrical pores or channels of an inert, non-conductive nanoporous electrode material. Track etch membranes, porous alumina, nanoporous conductive rubber polymers, metals, semiconductors, carbons and other solid materials have been used as templates to prepare nanometer-sized particles, fibrils, rods and tubules. The experimental set... 

During irradiation by swift ions, latent ion tracks are formed along the path of the ions. After irradiation, the material is subjected to chemical treatment leading to formation of the hollow channel from the latent ion track. The size and shape of the etched ion track is determined by the chemical processing. The etch process depends on the energy deposition density of the ion along its path, on the radiation... 

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