Track-etched membranes, synthetic

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... 

Other recent applications of AFM-SECM included the study of the iontophoretic transport of [Fe(CN)6]4 across a synthetic track-etched polyethylene terephthalate membrane by Gardner et al. [193]. They made the structure and flux measurements at the single pore level and found that only a fraction of candidate pore sites are active in transport. Demaille et al. used AFM-SECM technique in aqueous solutions to determine both the static and dynamical properties of nanometer-thick monolayers of poly(ethylene glycol) (PEG) chains end-grafted to a gold substrate surface [180]. 

Fabrication methods for 1-D PEDOT structures such as nanorod, tube and wire have been proposed via various synthetic routes microemulsion polymerization, template synthesis, electrochemical polymerization, and so forth. In the case of the template synthesis, various commercial templates were produced and available currently such as track-etched PC and AAO membranes, and mesoporous sihca. 

Flat-sheet asymmetric-skinned membranes made from synthetic polymers (also copolymers and blends), track-etched polymer membranes, inorganic membranes with inorganic porous supports and inorganic colloids such as Zr02 or alumina with appropriate binders, and melt-spun thermal inversion membranes (e.g., hollow-fiber membranes) are in current use. The great majority of analytically important UF membranes belong to the first type. They are usually made of polycarbonate, cellulose (esters), polyamide, polysulfone, poly(ethylene terephtha-late), etc. 

A number of different techniques are available to prepare synthetic membranes, ome of these techniques can be used to prepare polymeric as well as inorganic cmbranes. The most important techniques are sintering, stretching, track-etching, phase... 

The first procedure reported for the production of metal nanorods is called template synthesis.This method entails the preparation or deposition of the desired material within the cylindrical and monodisperse pores of a nanopore membrane. Martin and coworkers used polycarbonate filters, prepared by the track-etch method, and nanopore aluminas prepared electrochemically from Al foil, as template materials. This method allows the preparation of cylindrical nanostructures with monodisperse diameters and lengths, and depending on the nature of the membrane and the synthetic method used, these may be solid nanowires or hollow nanotubes. 

In developing these template synthetic methods, we made an interesting discovery. When these polymers are synthesized (either chemically or electrochemically) within the pores of the track-etched polycarbonate membranes, the polymer preferentially nucleates and grows on the pore walls [11,14,46]. As a result, polymeric tubules are obtained at short polymerization times (Fig. 16.2A). These tubular structures have been quite useful in our fundamental investigations of electronic conductivity in the template-synthesized materials (see below). In addition, tubular structures of this type have a number... 

Microfiltration and ultrafiltration membranes can be made from organic polymers or inorganic materials such as ceramic, glass, or metal or organic polymers. Materials used in MF and UF membrane fabrication are shown in Table 6.1. A number of different techniques are employed to prepare synthetic MF/UF membranes the most important are phase inversion, coating, sintering, and track etching. 

Although the template-based synthetic methods offer many advantages, there are some disadvantages. In all cases, the templates have to be removed and so these methods may not be suitable for making large quantities of nanorods. Also, a track-ion etched polycarbonate membrane may possess intersecting pores that will affect the homogeneity of the rods produced. 

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