Functionalization of MWNTs

The application of MWNTs in the field of polymer solar cells was presented by Ago et al. [311]. Here, a layer of CNTs served as a replacement for the common ITO hole-collecting electrode in a single layer PPV/Al diode (Fig. 64). The authors related the twofold enhancement of the EQE observed with the MWNT based device to the formation of a complex network with an increased interface area between MWNTs and PPV, in addition to a stronger built-in electric field as a result of the higher work function of MWNTs compared to the standard ITO electrode [311,312]. To determine whether electron or energy transfer processes dominate within MWNT PPV blends, their photophysical properties were studied by photoluminescence and PIA spectroscopy. The results confirmed nonradiative energy transfer from PPV singlet excitons to the MWNTs as the main electronic interaction [313]. 

Analogous results have been recently obtained by other research groups. The effect of -COOH- and phenol-functionalized CNTs on mechanical, dynamic mechanical and thermal properties of polypropylene (PP) nanocomposites were considered, and the results confirmed in both cases that the percentage crystallinity was found to increase on phenol and carboxylic functionalization of MWNTs. 

Fig. 13.2 Electrical conductivity (s) of the (a) PET/MWNT and (b) RG-O/epoxy nanocomposites as a function of MWNT and graphene loading. Inset a log-log plot of electrical conductivity vs. reduced MWNTand graphene loading. The solid lines are fits to a power law dependence of electrical conductivity on the reduced fillers loading (13.1) ((a) Reprinted with permission from Hu et al. (2006), Copyright 2006 Elsevier (b) reprinted with permission from Potts et al. (2011), Copyright 2011 Elsevier)...

Figures 6.18(a)-(c) show the variation of dielectric permittivity with frequency for PVDF filled with pristine, carboxyhc- and ester-functionalized MWNTs. The permittivity increases significantly for all composites when the filler content reaches the percolation threshold and above. Figures 6.19(a) (c) show the permittivity of pristine and chemically functionalized MWNT/PVDF compnasites as a function of MWNT volume fraction at 1 kHz.

Figure 6.20. Volume electrical conductivity of MWNT/PVDF nanocomposites as a function of MWNT loading a - high-shearing composites, b - low-shearing composites. Reproduced from [62] with permission...

Kerman et al, 2004 also described the label-free electrochemical detection of DNA based on the direct attachment of adenine probes to the sidewall and end of functionalized MWCNTs. The MWCNTs were attached onto the carbon paste electrode surface modified with thymine probes by hybridization between adenine and thymine. The combination of sidewall and end functionalization of MWNT showed enhancement of the guanine oxidation signal in the direct measurement compared to the ones from only end-modified MWCNT. 

Scheme 10.3. Schematic presentatiou for functionalization of MWNTs with chlorinated polypropylene (CPP) [51]...

Hwang and co-workers reinforced PMMA by addition of PMMA-grafted MWNTs. An inaease in modulus as measured by DMA from 2.9 to 29 GPa with addition of 20 wt.% MWNTs (dy/dVf 115 GPa) has been observed. The significant enhancement is primarily attributed to the successful functionalization of MWNTs. In addition, good dispersion and a continued inaease in modulus enhancement was observed up to 20 wt.% of MWNTs, which is unprecedented. ... 

Recently, it has been shown that inhalation of MWNTs caused suppression of the systemic immunity without resulting in significant lung inflammation or tissue damage [82,83]. Inhaled MWNTs in fact modified the functionality of spleen cells in exposed mice [82]. Notably, the activity of cyclooxygenase (COX) enzymes in spleen was affected as a response to a cytokine (TGF(5) released from the lungs. This cytokine activated the COX pathway in the spleen, triggering T-cell dysfunction and systemic immunosuppression [83]. 

The vertically aligned monolayer of MWNTs was obtained by dipping the polyelectrolyte-modified substrate into a tetrahydrofuran suspension of the functionalized MWNTs. 

Guo et al. (2007) have used water-soluble MWNTs labelled with 99l"Tc for biodistribution study in mice. There was no sign of renal or other severe acute toxicity responses consistent with the results of Singh et al. (2006). This work also suggests that functionalization of CNTs might improve their biocompatibility of CNTs. 

Polymer nanotubes composites are now extensively studied. Indeed, one may associate the properties of the polymer with those of nanotubes. This is the case of the mechanical reinforcement of standard polymer for example, but also one can take advantage of the specific electronic properties of the nanotubes. Therefore, we prepared composites with either saturated polymers like polymethylmethacrylate and MWNTs [27]. The electrical conductivity of these compounds as a function of the nanotube content exhibits for example a very low percolation threshold, (a few % in mass) and therefore they can be used as conducting and transparent layers in electronic devices such as Light Emitting Diodes (LEDs). Another type of composite that we have studied is based on the use of a conjugated polymer, polyphenylene-vinylene (PPV) known for its photoluminescence properties and SWNTs. We prepared this composite by mixing SWNTs to the precursor polymer of PPV. The conversion into PPV was subsequently performed by a thermal treatment at 300°C under dynamical vacuum [28],... 

The same platform was used to prepare BSA-functionalized magnetic MWNTs.32 After magnetic separation, those nanotubes with iron or iron oxide encapsulation were isolated and coated with anti-E coli 0157. The resulting immunomagnetic MWNTs were evaluated in immunomagnetic separation of E. coli 0157 H7 cells in pure and... 

Double-walled carbon nanotubes (DWNTs), first observed in 1996, constitute a unique family of carbon nanotubes (CNTs). -2 DWNTs occupy a position between the single-walled carbon nanotubes (SWNTs) and the multiwalled carbon nanotubes (MWNTs), as they consist of two concentric cylinders of rolled graphene. DWNTs possess useful electrical and mechanical properties with potential applications. Thus, DWNTs and SWNTs have similar threshold voltages in field electron emission, but the DWNTs exhibit longer lifetimes.3 Unlike SWNTs, which get modified structurally and electronically upon functionalization, chemical functionalization of DWNTs surfaces would lead to novel carbon nanotube materials where the inner tubes are intact. The stability of DWNTs is controlled by the spacing of the inner and outer layers but not by the chirality of the tubes 4 therefore, one obtains a mixture of DWNTs with varying diameters and chirality indices of the inner and outer tubes. DWNTs have been prepared by several techniques, such as arc discharge5 and chemical vapor depo-... 

Besides covalent functionalization of carbon nanotubes, non-covalent interaction between CNTs and polyurethane can also help fabricate uniform CNT dispersion nanocomposites. A dominant improvement in the dispersion of MWNTs in hyperbranched polyurethane (HBPU) matrix was found, and good solubility of... 

Mondal et al. investigated the influence of functionalized MWNTs on microstructure and water vapor transport properties of SPU membranes (95). The presence of MWNT was expected to decrease the permeability due to the more tortuous path for the diffusing molecules that must bypass through impermeable nanoparticles. Experimental results revealed that there were about 20% reductions... 

Figure 11.6. Electrical conductivity of MWNT/PVA and VGCF/PVA films, as a function of the filler content. Reprinted with permission from reference (29).

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