Nanotube silane

K. Yang and M. Gu, "Enhanced thermal conductivity of epoxy nanocomposites filled with hybrid filler system of triethylenetetramine-functionalized multi-walled carbon nanotube/silane-modified nano-sized silicon carbide," Composites Part A, vol. 41, pp. 215-221,2010. 

Separation of SWNTs based on chirality and diameter with surfactants has also been evidenced by density-gradient ultracentrifugation [86]. Finally, a recent study has demonstrated the separation of semiconducting nanotubes from metallic ones by chemical interaction of the former with attached amine-terminated silane molecules assembled on a silicon wafer. In a separate experiment, metallic nanotubes were also... 

Abstract Polyferrocenyldimethyl-silane (PFS) diblock copolymers with polyisoprene (PFS-PI) or with polydimethylsiloxane (PFS-PDMS) self-assemble in simple alkane solvents to form what appear by TEM to be dense flexible cylinders (nanowires) or nanotube-like structures. Typical widths are on the order of 20 to 30 nm, with variable lengths often greater than 10 un. The structures that form, and the dimensions of the tube-like structures or wires, depend upon the composition of the polymers and the lengths of the blocks. Light scattering experiments show that the PFS-PDMS (block ratio 1 12) solutions aged... 

We have used these silica nanotubes as test vehicles to illustrate the power of the template method for preparing nanombes for biomedical and biotechnological applications [4,5]. Silica nanombes are ideal for such proof-of-concept experiments because they are easy to make, readily suspendable in aqueous solution, and because silica surfaces can be deiivatized with an enormous variety of different chemical functional groups using simple silane chemistry with commercially available reagents [4,5]. 

Another example concerns the immobilization of a biocatalyst—the enzyme glucose oxidase (GOD)—to the silica nanotubes [4]. GOD was immobilized, on both the inside and outside surfaces, via the aldehyde silane route. These GOD-nanotubes (60 nm diameter) were dispersed into a solution containing 90 mM glucose and also the components of the standard dianisidine-based assay for GOD activity. A GOD activity of 0.5 0.2 units per milligram of nanotubes was obtained. These studies also showed that protein immobilized via the Schiff base route is not leached from the nanotubes, where GOD activity ceased when the nanotubes were filtered from the solution. 

COLOR FIGURE 24.3 Photographs of vials containing nanotuhes modified with two different fiuorophores in two different solvent medium. (A) Cyclohexane (upper) and water (lower) under UV light excitation after addition of 10 mg of nanotubes with dansylamide on inner and Cis on outer surfaces, (B) quinineurethan on inner and no silane on outer surfaces, (C) 10 mg of both (A) and (B) nanotubes. 200 nm diameter nanotuhes were used. (From Mitchell, D.T., Lee, S.B., Trofin, L., Li, N., Nevanen, T.K., Sdderlund, H., and Martin, C.R., J. Am. Chem. Soc., 124, 11864, 2002. With permission.)... 

The next step Ifom Silicon-based sheet polymers to tubular structures has been performed so far only on the computer. In Chapter 17, Th. Frauenheim et al. describe the structure and the electronic properties of silicide, silane and siloxane nanotubes. The structures can be understood in terms of conventional graphitic carbon nanotubes by replacing the flat hexagons by puckered rings. The electronic properties depend on the tube diameter. Potential applications are discussed. 

Figure 17.3. Examples of the structures of silicide and silane nanotubes with (8,0) (left panel) and (8,8) (right panel) chirality. From top to bottom are shown pure silicide (Si ) and the silanes (SiH-io) and (SiH-sf), in each case in top and side views (taken from ref...

Figure 17.4. Strain energies (left) and gap sizes (right) as functions of mean diameter are shown for all calculated (n,0) and (n,n) silicide and silane nanotubes. The gap sizes of planar reference structures are symbolized by a single line due to nearly equal gap widths of 2.49 eV and 2.50 eV for planar Si and SiH, respectively. (Taken from ref.

Additionally, the mechanical properties of silicide and silane nanotubes have been obtained by DFTB calculations. The data clearly indicate that Si-based nanotubes are less stiff than other nanotubes hitherto considered, such as those made of P, BN, or C. Compared with typical values of Young s moduli of about 1.2 TPa for CNTs, the values for Si-based tubes are of the order of the bulk modulus of crystalline silicon, 98 GPa, predicted with the same theoretical method. Depending on tube diameter and type, the Young s moduli vary between 55 and 80 GPa. 

Viewed from above the layer, the structure clearly resembles a graphenelike layer, although it is puckered in a similar way as in the silicide, silane, and phosphorus cases. Thus, the question arises as to whether siloxenes may form stable tubular structures as predicted for hypothetical silicides, silanes, and black phosphorus nanotubes. The experimentally synthesized siloxene consists of hexagonal puckered layers, in which the Si-Si bond distance is 2.34 A, the Si-H bond length is 1.54 A, and the Si-O bond length is 1.60 A. The Si-0-H bond angle is 115°. 

Eleetronieally, the flat sheet as well as all the nanotubes considered here were determined to be semieonducting. In Figure 17.7, the gap sizes of nanotubes are shown as a function of the mean diameter. The gap sizes grow from about 1.5 eV for the smallest (n,0) nanotube towards the value for flat siloxene sheets (1.9 eV) as the tube diameter increases, as in the case of silicides and silanes discussed above. 

As noted earlier, one of the most important attributes of a nanotube is that it has distinct inner and outer surfaces that can be differentially chemically and biochemically functionalized. The template method provides a particularly easy route to accomplish this differential functionalization. The details of nanotube modifications using differential silane chemistry on nanotubes are available elsewhere. In the following paragraphs, we briefly describe the results of differential-functionalized nanotubes and their applications in highly selective chemical and biochemical extractions. ... 

To prove this concept, a set of nanotubes was prepared with the green fluorescent silane A-(triethoxysilylpropyl)dan-sylamide attached to their inner surfaces and the hydrophobic octadecyl silane (Cjs) to their outer surfaces. These nanotubes were added to a vial containing water and the immiscible organic solvent cyclohexane, which were mixed and allowed to separate. Because these nanotubes are hydrophobic on their outer surfaces, they partition into the (upper) cyclohexane phase (Figure 20.9b). This may be contrasted to nanotubes that were labeled on their inner surfaces with the blue fluorescent silane triethoxysilylpropylquinineurethan, but were not labeled with any silane on their outer surfaces. When the same experiment is done with these nanotubes, the quinineurethan fluorescence is seen only from the aqueous phase (Figure 20.9a). When both sets of nanotubes are added to the solvent mixture... 

After the initial research on CD nanotubes by Harada et al. and by Wenz et al. the intriguing systems have been widely extended to various functional polymers such as conjugated polymers (Fig. 3d), including poly(aniline) (PANI), poly(thiophene) (PT), poly(silane) (PS), etc., which can also thread through the CD cavities to form the polyrotaxane-type complexes (Fig. 3b) [35-50]. In view of the fundamental research on the conjugated polymers, the advantageous point of the CD nanotube systems is that the functional polymers can be well insulated as an individual polymer chain even in their solution and in the solid state. Since the conjugated polymers... 

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