Polymer nanostructures track

Within the scope of thermoelectric nanostructures, Sima et al. [161] prepared nanorod (fibril) and microtube (tubule) arrays of PbSei. , Tej by potentiostatic electrodeposition from nitric acid solutions of Pb(N03)2, H2Se03, and Te02, using a 30 fim thick polycarbonate track-etch membrane, with pores 100-2,000 nm in diameter, as template (Cu supported). After electrodeposition the polymer membrane was dissolved in CH2CI2. Solid rods were obtained in membranes with small pores, and hollow tubes in those with large pores. The formation of microtubes rather than nanorods in the larger pores was attributed to the higher deposition current. 

From the standpoint of nanostructuring, ion track membranes are unique in that every track can be seen as an individual nanostructure with an extreme aspect ratio The length of the channel is usually in the 10- to lOO-pm range and spans the whole thickness of the exposed film. The width of the channels, typically in the range of 100 nm to several micrometers, is defined by the ion and its energy as well as the etching parameters after ion bombardment. Furthermore, the polymer and the process parameters influence the exact shape of the channel formed [38]. 

Hard template method has been used for the 1-D nanostructures such as nanotubes, nanorods and nanofibers of conducting polymers. The commonly used templates are AAO membrane, and track-etched PC membrane, whose pore size ranges from 10 nm to 100 pm. Hard template methods for synthesizing conducting polymer nanomaterials have been extensively reviewed in recent years [156-160]. 

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... 

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. " °°... 

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