Carbon Nanotubes for Targeted Drug Delivery by Md Saquib Hasnain & Amit Kumar Nayak

Author:Md Saquib Hasnain & Amit Kumar Nayak
Language: eng
Format: epub
ISBN: 9789811509100
Publisher: Springer Singapore

9.2 Use of CNTs in Solubility Enhancement

CNTs with distinctive structure and characteristics are interesting in building blocks of significant practical consideration for devices as well as products. Nevertheless, a severe threat to their further advancement is the insolubility or low dispersibility of pristine CNTs in prevalent solvents. Various efforts have been made to achieve homogeneous CNTs dispersions in both aqueous as well as organic media (Banerjee et al. 2005; Georgakilas et al. 2002; Hamon et al. 1999; Hong et al. 2005; Huang et al. 2002; Hudson et al. 2004; Kong et al. 2004; Qin et al. 2004; Qin et al. 2003; Sinani et al. 2005; Zhao et al. 2002). Chemical changes in sidewalls, defect sites and open ends often leads to changes in the structural, mechanical as well as electronic features of CNTs among these techniques. (Garg and Sinnott 1998; Monthioux et al. 2001). Non-covalent methods were then developed based mainly on physical surfactant or polymer adsorption, illustrating the benefits of leaving the electronic structure integrated of CNTs. However, non-covalent functionalization is a very successful technique to disperse SWNTs than MWNTs, since the length of the polymer chain and the coverage of surface required to induce steric repulsion in MWNT dispersions are exceptionally high in comparison to those required to disperse SWNTs (Shvartzman-Cohen et al. 2004). Conversely, by employing increased levels of surfactants or polymers, such as, creating composite materials, acquiring CNT dispersions will cause inconvenience in their further processing. Hence, from the standpoint of both fundamental research and technical implementation, an efficient noncovalent sidewall functionalization method for MWNTs is extremely desirable.

Polyaniline (PANI) is a major conductive polymer with outstanding environmental stability, high electrical conductivity as well as inimitable redox characteristics. The composite studies of CNT/PANI have recently disclosed excellent relationships among the parts, in particular when polymerization happened in the presence of CNTs (Zengin et al. 2002). The resulting composites in standard solvents, however, are insoluble and hard to process, which significantly hinders their practical applications. PANI derivatives (e.g., polyanisidine and emeraldine base) were used to enclose CNTs in efforts to solubilize CNT/PANI composites in organic solvents. Sulfonated polyaniline (SPAN) synthesis, which has impending utilizations in electronic devices, is the most efficient approach for soluble PANI conducting (Chen and Hwang 1996; Wei et al. 1996; Yue et al. 1991). The mixing of CNTs and SPAN into composite materials will expand the utilization of CNTs and SPAN via tailoring its solubility features. For example, the covalent functionalization-generated composite SWNT/poly (m-aminobenzene sulfonic acid) indicated augmented sensor effectiveness for NH3 detection (Bekyarova et al. 2004; Zhao et al. 2004). It is revealed that the water-soluble conductive polymer (SPANs) for non-covalently functionalizing graphitized MWNTs displays the fine crystalline structure as well as higher conductivity. The functionalization was based on aniline and MWNT in situ polymerization followed by chlorosulfonic acid sulfonation in a nonreactive solvent and hydrolysis. The lengths and surface structure of MWNTs was not disrupted by SPAN incorporation. The intensely water-soluble SPAN-functionalized MWNTs (MWNT/SPAN composite) create many unique opportunities for future technological applications.

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