Poly nanochannels

A particularly interesting study that exemplifies the effect of nano-confinement is one where poly(phenylene vinylene) PPV, a luminescent polymer, was incorporated into the channels formed from these polymerized hexagonal phases [78]. These hexagonal PPV nanocomposites exhibited a significant enhancement in the photoluminescence quantum yields, from ca. 25 to 80%. The origin of this enhancement is ascribed to the prevention of the formation of poorly emissive inter-chain excitonic species as a result of the confinement of the PPV chains into well-defined and well-separated nanochannels. An important feature of these nanocomposites was that they could be readily processed into thin films and fibres and, more importantly, macroscopic alignment of the channels encapsulating the PPV chains led to polarized emission [79]. 

Fig. 6 (a) NMR spectra of Poly(methyl methacrylate) (PMMA) obtained from the nanochannels of [Cu2(L)2(ted)] and the bulk condition in nitrobenzene- / at 110°C. (b) Plot of nanochannel size effect on tacticity of PMMA... 

Fig. 8 NMR spectrum of poly(/ -DVB) obtained from the nanochannel of [Zn2(bdc)2ted] in DMSO- /. The ratio of the peak intensities of a to those of b, c, and d is found to be 2 5...

Alumina nanoporous templates have also been used in gas-phase growth of CPNTs. It has been reported that isolated nanotubes consisting of poly(p-phenylenevinylene) (PPV) and carbonized-PPV bilayers can be synthesized in an alumina template by chemical-vapor deposition (CVD) polymerization. In a smdy done by Kim and colleagues, CVD polymerization of PPV was carried out by passing monomer vapor through a pyrolysis zone at 625 °C to form precursor polymer nanotubes on the inner surface of the alumina nanochannels. The nanotubes were further thermally treated in vacuum at 270 °C for an extended time (14 h) to be converted into PPV nanotubes. In order to create PPV/ carbonized PPV bilayer nanotubes, the PPV nanotubes were then carbonized at 850 °C... 

The fabrication of polypyrrole wires via electropolymerization within poly(methyl methacrylate) nanochannels on an indium tin oxide (ITO) substrate was reported by Chen et al. [53]. The electrochemical synthesis of polypyrrole was performed by a cyclic voltammetry method in aqueous 0.1 M NaC104 containing 0.1 M pyrrole monomer. The potential was scanned 10 times between -0.7 and +0.6 V vs. Pt at a scan rate of 100 mV s . The nanochannels act as templates for electropolymerization of polypyrrole nanowires. 

In vinyl acetate (VA) bulk or solution polymerization systems, side reactions (e.g., chain transfer or termination) will inevitably occur to produce highly branched poly(vinyl acetate) (PVA), based on the nonconjugated nature of the propagating radical. However, the polymerization of VA in nanochannels of [Cu2(terephthalate)2ted] effectively suppresses chain branching during the polymerization, and this results in a constrained chain growth in the narrow 1-D nanochannels [26]. 

Ultra-thin conformal coatings in the range of 10-100 nm using poly(ethyl 2-cyanoacrylate) andpoly(/ -xylylene) have been synthesized via vapor deposition in the confined nanochannels of anodized alumina membranes [110]. After the removal of the inorganic anodized alumina membrane, nanotubes with a precisely controlled wall thickness could be isolated. 

Electrokinetic Flow and Ion Transport in Nanochannels, Fig. 3 Molecular model showing a single strand of poly(dC) DNA passing through an a-hemolysin protein pore in a lipid bilayer membrane. The surrounding water molecules have not been shown [9]... 

In an opposite sense to the nanochannels, LbL assembly has been performed on microscopic protmsions to afford uniformly coated microneedle arrays, which are under development for transcutaneous therapeutic delivery.The precise control over coating thickness and composition that is offered by the LbL approach is a key advantage for this type of technology. The laboratories of Hammond and Irvine have demonstrated the systematic growth of alternating layers of poly(P-amino ester)s (PBAEs) and plasmid DNA, PBAE, and... 

A significant nanochannel effect was also observed on the stereoregularity of the polymer product, in that the tacticity of the polymers was found to be strongly dependent on the size and shape of the pores [12, 13]. For example, the polymerization of methyl methacrylate (MMA) in [Cu2(2,5-dimethoxyterephthalate)2(ted)] gave poly(methyl methacrylate) (PMMA) with high isotactic and heterotactic triad fractions (m = 54 %), and therefore represents one of the most effective systems for... 

Preparation of Structured Materials Rzayev and Hillmyer [311] developed a novel method for preparing nanochannel array plastics with tailored surfaces by self-assembly, alignment of polystyrene (PS)-poly(dimethy-lacrylamide) (PDMA)-PLA triblock copolymers, subsequent selective hydrolysis and removal of PLA segments from the aligned materials. The nanochannel surface after removal of PLA segments is covered with PDMA. 

Anodic aluminum oxide (AAO) membranes are a popular choice as templates for nanowires and nanotubes. As such they have been used to fabricate polymer nanochannels, mostly via melt inbltration, which has given the possibility of stud dng the wetting and flow of polymer melts in the alumina pores. In one such work an enhanced flow rate of poly-caprolactone was observed when mechanical vibration is applied to the AAO during the filling process. It... 

L. Pellegrino, Y. Yanagisawa, M. Ishikawa, T. Matsumoto, H. Tanaka, and T. Kawai, [Fe, Mn]304 nanochannels fabricated by AFM local-oxidation nanolithography using Mo/poly(methyl methacrylate] nanomasks, Adv. Mater., 18, 3099 [2006]. 

Another simple approach to glucose detection was recently proposed by Tsai and co-workers, who employed atomic force microscopy (AFM) lithography to score nanochannels in a poly(methyl methacrylate)(PMMA) film coated onto a platinum substrate.Subsequent electrodeposition of the GOx enzyme into the nanochannels resulted in the growth of horizontal GOx nanorods, with heights as small as 80 nm. The analytical figures of merit for this approach, which was tested for 25x8 pm long chaimels, did not compete with the above examples, but the sensor is yet to be optimised and the simplicity of the approach makes it accessible to any research laboratory. 

Poly(vinyl alcohol) (PVA) substrates coated with a non-porous hydrophilic polymer/multiwalled nanotube (MWNT) nanocomposite layer have been put forward for potential use in oil/water emulsion separation (Wang et al, 2005). Specifically, it has been proposed that CNTs could improve the flux rate for the formation of hydrophilic nanochannels for water transfer through nanocomposite membranes. The immobilization of CNTs in hydrophobic membrane pores was shown to have a favourable effect on water-membrane interactions and to promote higher vapour permeability, since liquid was prevented from entering the membrane pores (Gethard et al, 2011). The literature also mentions improvements in water flux and selectivity when polymeric membranes are loaded with hydrophilic nanofiUers, including silica (Bottino et al, 2001), ZrOj (Bottino et al, 2002) and HO2 (Yang et al, 2006). 

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