Nanocoils

Helical (carbon) nanocoils have received attention recently255-257 for their properties as field emitter and thus for the fabrication of flat panel field emission displays. The properties depend on the electrical field generated due to the helical nanostructure, and to the characteristics of the tip of the carbon nanocoil. In fact, carbon... 

Fig. 11 FESEM image of the Titania nanocoil array obtained by controlled anodization of Ti foils. Adapted from Perathoner et al.25g... 

The preparation of Titania nanocoils has been yet not investigated in literature. However, quite recent results258 show that the effective structure of Titania nanotube likely produced by controlled anodization process is that of a helical (compressed) nanocoil. Fig. 11 shows this concept. It was also demonstrated that the formation of these helical nanocoils improves the photo-generated current compared to samples after short anodization where only a Titania layer is formed. 

A specific and peculiar additional possibility was suggested " from the observation that an ordered array of Ti02 nanocoils forms in particular conditions of synthesis by anodic oxidation.The interesting aspect is that in such nanostructures, photo-induced current generates a local magnetic field which influences the reactivity properties of catalytic... 

Fig. 7 FESEM images of titania nanocoil produced by anodic oxidation (a). The cartoon shows schematically the photocurrent generated by light irradiation of nanocoil containing a catalyst particle (b) and the associated magnetic field (c). Source Centi and Perathoner. ...

Figure 3.13 (Top) TEM micrographs of (a-i) silver nanocoils prepared by backfilling, (j-k) helical mesoporous silica grown inside nanochannels of different sizes (indicated below each micrograph). (Bottom) Schematic of differing confined nanostructural evolution with decreasing diameter of the nanochannels [56],...

Perathoner S, Passalacqua R, Centi G, Su DS, Weinberg G. Photoactive titania nanostructured thin films. Synthesis and characteristics of ordered helical nanocoil array. Catal Today. 2007 122 3-13. 

Some nano-materials and nano-devices fabricated primarily for functional applications, such as nanopowder [26], nanowire [27], nanobelt [28], nanotube [29] as well as nanocoil [30],... 

Korgel BA (2004) Materials science - self-assembled nanocoils. Science 303(5662) 1308-1309... 

It was not long after the discovery of carbon nanotubes before specimens with coiled or helical shapes were observed. These helical nanotubes (hMWNT) are often found as by-product in the synthesis of multiwalled nanotubes, yet by now a directed preparation has succeeded as well. Their extraordinary shape turns the helical nanotubes into an interesting subject of research as the expected electronic properties like inductive effect under electrical current should enable an application, for example, as nanocoils. ... 

It was revealed that at deposition of the nanocomposite films in the Ar + O2 gas mixture the region of the superparamagnetic state was expanded far beyond percolation threshold %c determined from the electrical properties of the films deposited in pure Ar. An inductive contribution in equivalent circuits of the studied films shows that the currentconducting routes within the film bulk look like a system of nanocoils embedded in the alumina matrix. 

Barranco, V., V. Celorrio, M. J. Lazaro, and J. M. Rojo. 2012. Carbon nanocoils as unusual electrode materials for supercapacitors. Journal of the Electrochemical Society... 

Rakhi et al reported the conducting-polymers (polyaniline [PANI] and PPy)-coated carbon nanocoils (CNCs) as efficient binder-free electrode materials for supercapacitors for the first time, in which the CNCs acted as a perfect backbone for the uniform distribution of the conducting polymers in the composites [16]. Ihe SC and maximum storage energy per unit mass of the composites were found to be comparable to one of the best-reported values for polymer-coated MWNTs. Dumanli et al. prepared the chemically bonded carbon nanofibers (CNFs)-PPy composite via electro-polymerization of Py on CNFs [17]. It showed that the final capacitance values were highly dependent on the number of deposition cycles and deposition rates. The best result for the coiled CNF-PPy composite system was found to be 27.6 C/cm at six times cycling using 25 mV/s. 

Self-Assembled Nanotubes and Nanocoils from TT-Conjugated Building Blocks... 

Keywords jr-Conjugation Chirality Nanocoil Nanotube Self-assembly... 

Ajayaghosh et al. have reported nanocoiled assemblies of a short-chain oligo(p-phenylene vinylene) derivative 3 (Fig. 3a) in dodecane [14]. It is noteworthy that formation of the coiled assembly requires the presence of... 

Fig. 3 Molecular structures of 3a and 3b (a). AFM images of the nanocoils from 3b by self-assembly (b) and co-assembly of 3a with 9 mol % of 3b (c). M left-handed. P right-handed. The AFM images were provided courtesy of Prof. Ayyappanpfllai Ajayaghosh of National Institute for Interdisciplinary Science and Technology...

Since porphyrin and phthalocyanine derivatives possess excellent electronic and photophysical properties, they have been extensively studied as functional components for a wide variety of crystalHne, liquid crystalline, and polymeric materials. Increasing attention has also been paid to well-defined nanostructured assemblies of such organic dyes, and indeed, many examples of fibers, tapes, and vesicles have been reported [20]. However, only two examples are known for the formation of nanotubes and nanocoils. 

Fig. 8 Molecular structure of 8a (a). Electronic absorption spectral change of 8a upon self-assembly in THE (Imgml ) (b). SEM micrograph (c), proposed structure (d), and TEM micrograph (e) of tubularly assembled 8a. Proposed structure of the nanocoils of self-assembled 8a (f). TEM micrograph of a mixture of nanotuhes and nanocoUs formed by the self-assemhly of 8a in a mixture of THE and water (8/2 v/v) (1 mgml )...

Differing from 8a and 8b, norbornene-appended HBC 8c (Fig. 10), designed for ROMP, affords nanocoUs as well as nanotubes (Fig. 12) [35]. By choosing appropriate conditions, either nanocoils or nanotubes are selectively formed. For example, by EtzO vapor diffusion into a CH2CI2 solution of 8c (0.65 mM) at 15 °C, the nanocoils form exclusively. At the same time, when the vapor diffusion is conducted at 25 °C at a lower concentration of 8c (0. 22 mM), the nanotubes can be obtained as the sole product. As observed by TEM and SEM, the nanocoil consists of a 20-nm-wide bilayer tape with 30 nm in diameter and 60 nm in pitch (Fig. 13a), while the nanotube possesses a diameter of 20 nm and a wall thickness of 3 nm (Fig. 13b). Interestingly, when the suspension of the nano coils is allowed to stand for 5 days at... 

Fig. 12 Synthetic approaches to the surface-polymerized nanotube and nanocoil of 8c by post-ring-opening metathesis polymerization (ROMP)...

Fig. 13 SEM and TEM (inset) micrographs of the nanocoUs (a) and nanotubes (b) of self-assembled 8c, formed by Et20 vapor diffusion into CH2CI2 solutions of 8c. SEM and TEM (inset) micrographs of the nanotubes of self-assembled 8c, formed upon immersion of the nanocoils in Et20/CH2Cl2 (9/1) at 25 °C for 5 days (e). SEM and TEM (inset) micrographs of the surface-polymerized nanocoUs of 8c formed by post-ROMP (d)...

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