Surfactant Concentration Dependent Spectral Effects of Oxygen and Depletion Interactions in Sodium Dodecyl Sulfate Dispersions of Carbon Nanotubes

Abstract

Quenching of optical absorbance spectra for carbon nanotubes (CNTs) dispersed in sodium dodecyl sulfate (SDS) has been observed to be more pronounced at higher concentrations of the surfactant. The protonation-based quenching behavior displays wavelength dependence, affecting larger diameter nanotube species preferentially. Although absorbance may be recovered by hydroxide addition, pH measurements suggest that hydrolysis of SDS does not play a major role in the short term quenching behavior at high SDS concentrations. The degree of quenching is observed to correlate well with an increase in attractive depletion as SDS concentration is increased, while the extent of depletion is found to depend heavily on the concentration of preparation in comparison to the final SDS concentration. Attractive depletion in SDS is also found to be preferential for CNTs of larger diameter. It is proposed that depletion enhances the quenching effect due to close association of CNT-SDS complexes providing higher SDS densities on the CNT surface, leading to further oxidation. In addition, the quenching behavior in SDS is found to strongly suppress the optical and Raman signal from metallic nanotube species even at high pH. Displacement of SDS by sodium deoxycholate as a secondary surfactant is able to reverse the effects of protonation of metallic species, whereas hydroxide addition is only partially effective.

Origin of the Surfactant‐Dependent Redox Chemistry of Single‐Wall Carbon Nanotubes

“…SC and DOC disperse SWCNTs better than SDS solution . The SWCNTs show intense absorption, fluorescence, or Raman spectra owing to the prevention of oxidation, likely as a result of the dense coating of the SWCNTs with the surfactants as previously discussed . In particular, SC was shown by MD simulations to have a hydrophobic interaction with the SWCNT surface because of its slightly bent but rigid steroid ring with a hydrophobic face .…”

“…At pH 5–6, the potential is approximately 900 mV. Because the potential is regulated by the proton concentration, the SWCNT oxidation is significantly affected by variations in the pH value . In the absence of additives, the pH values of the SDS and SUS solutions were approximately 5–6, whereas that of the SDBS solution was approximately 4–5.…”

“…At pH 5-6, the potential is approximately 900 mV.B ecause the potential is regulated by the proton concentration, [9] the SWCNT oxidation is significantly affectedb yv ariationsi n the pH value. [5,[39][40][41] In the absence of additives, the pH values of the SDS and SUS solutions were approximately 5-6, whereas that of the SDBS solution was approximately 4-5. The spectra in the presence of K 2 IrCl 6 were therefore measured at pH 5-6 for SDS and SUS and at pH 4-5 for SDBS to avoid such pH influences;t he final pH values were adjusted by using hydrochloric acid (HCl) or sodium hydroxide (NaOH).…”

“…[53] The SWCNTss how intense absorption, fluorescence, or Raman spectra owing to the prevention of oxidation, likely as ar esult of the dense coating of the SWCNTsw ith the surfactants as previously discussed. [41] In particular, SC was shown by MD simulations to have ah ydrophobic interaction with the SWCNT surfaceb ecause of its slightly bent but rigid steroidr ing with ah ydrophobic face. [36] It was reported that theses urfactants have moderate CMCs, that is, approximately 13 mm (0 .6 wt %) for SC and 7mm (~0.3 wt %) for DOC, [54] which is comparable to or greater than the CMC of SDS.…”

Ethyl Acetate/2‐Butanol as Effective Green Chromatography Solvent for Coexisting Anionic Surfactants

“…Sodium lauryl sulfate (SLS) is popularly used as a foaming and cleaning agent in shampoo and washing products. Aqueous solutions of SLS are commonly used for the dispersion of carbon nanotubes (CNT) [1]. Its capability of binding with oxidised iron in blood has been very useful in the analysis of blood [2].…”