Association of DNA-Stabilized Carbon Nanotubes and Cationic Surfactants: Ionic Strength and Chain Length Effects

Processing carbon nanotubes (CNTs) into functional materials requires usage of multicomponent systems. Additives such as ionic surfactants, complex macromolecules (i.e., DNA, proteins), or colloidal nanoparticles are used for this purpose. Unfortunately, the high intrinsic nonideality of these systems makes predictions and simulations of their behavior challenging. That is why experimental investigations on the overall colloidal behavior are fundamental in developing CNT-based technologies. To that purpose, we have recently started a systematic characterization of (pseudo)ternary systems containing carbon nanotubes. In a previous study, we have characterized the re-entrant behavior of single-stranded DNA (ssDNA)/CNT in the presence of an oppositely charged surfactant. The ratio between ssDNA/nanotubes and surfactant defines the overall associative behavior. Irreversible aggregation is found close to the isoelectric point, while negatively or positively charged surfactant–ssDNA/nanotube complexes appear at ssDNA or surfactant (redispersion) excess, respectively. Here, we present a detailed investigation on the effects of surfactant chain length and ionic strength on the nanotubes’ associative behavior by considering an approach involving different and complementary experimental techniques. The associative behavior is related to the micellization ability of surfactant. Interestingly, no redispersion is found for short chains with n < 14. The phase behavior is analyzed in comparison with the one of polyelectrolyte–surfactant–water system.