Enhanced Solubilization of Carbon Nanotubes in Aqueous Suspensions of Anionic–Nonionic Surfactant Mixtures

Abstract

Single-walled carbon nanotubes (SWCNTs) suspensions in aqueous solutions of sodium dodecyl sulfate (SDS) and saturated fatty acids (Cn) are studied. The quality of the dispersions is analyzed by photoluminescence spectroscopy (PL) as a function of the Cn chain length. Resonant Raman scattering (RRS) measurements and molecular dynamics (MD) simulations were also carried out in order to study the effect of the surrounding medium on SWCNTs properties in suspensions. Both PL and RRS data indicate an increased individualization of SWCNTs in the dispersions for Cn's having an alkyl chain longer than SDS. MD simulations showed the formation of mixed Cn-SDS aggregates around a nanotube in water and a Cn binding energy to the nanotube wall that increases linearly with chain length. The enhanced solubilization of SWCNTs is thus interpreted in terms of the reduced electrostatic repulsion within the surfactant aggregates and the increased binding energy to the nanotube wall. Powders prepared by the evaporation of dispersions of Cn's and SWCNT bundles in ethanol were also studied by RRS in the radial breathing mode (RBM) frequency range. All the measured RBM frequencies exhibit a blue-shift (Δω) with respect to the values obtained for pristine SWCNT powders. Remarkably, nanotubes with diameters smaller than 1.0 nm show Δω in the range 2.5−4.5 cm −1 while those having diameters larger than 1.0 nm exhibit Δω in the range 6.5−8.0 cm −1 . MD simulations showed that large diameter nanotubes encapsulate Cn's into their cores, thus justifying the increased hardening of the RBM mode.

A Comparative Study on Graphene Oxide and Carbon Nanotube Reinforcement of PMMA-Siloxane-Silica Anticorrosive Coatings

“…Using the method of Alves da Cunha et al, the SWCNTs were dispersed in sodium dodecyl sulfate surfactant (SDS, Sigma-Aldrich) and hexadecanoic acid (palmitic acid, Sigma-Aldrich). 4 Then, 0.3 mg of CNTs were added to 10 mL of SDS 1% water solution, and after 30 min in an ultrasonic bath, 110 mg of palmitic acid was added. After 20 min of further sonication, the solution was centrifuged for 3 h at 4000 rpm.…”

Protective Coatings Based on PMMA–Silica Nanocomposites Reinforced with Carbon Nanotubes

“…Alternative approaches have been developed to disperse individual CNTs by noncovalent functionalization employing a wrapping agent, typically a surfactant or an organic polymer. A successful separation of CNTs leading to a stable suspension in aqueous solutions of sodium dodecyl sulfate (SDS) surfactant with coaddition of saturated fatty acids was recently demonstrated [17]. Following on from previous work on PMMA-silica coatings containing CNTs [7], we have successfully prepared CNT-reinforced protective hybrid coatings on carbon steel in this study.…”

“…Single-wall CNTs were purchased from Dropsens for incorporation into the two hybrids BPO0.01 and BPO0.05. In one pretreatment prior to their incorporation, the CNTs were dispersed using the method described by Alves da Cunha et al [17], in which aqueous solutions of SDS surfactant (Sigma-Aldrich) and hexadecanoic acid (palmitic acid, Sigma-Aldrich) are used. The dispersion procedure, schematized in Figure 2a, starts from raw CNTs and is based on the nonpolar groups of SDS and palmitic acid promoting physical interaction with CNTs, while polar groups of these two chemicals interact with water [17].…”

“…In one pretreatment prior to their incorporation, the CNTs were dispersed using the method described by Alves da Cunha et al [17], in which aqueous solutions of SDS surfactant (Sigma-Aldrich) and hexadecanoic acid (palmitic acid, Sigma-Aldrich) are used. The dispersion procedure, schematized in Figure 2a, starts from raw CNTs and is based on the nonpolar groups of SDS and palmitic acid promoting physical interaction with CNTs, while polar groups of these two chemicals interact with water [17]. After dispersion in SDS and palmitic acid, the CNTs were added at the end of the PMMA-silica hybrid synthesis, at a C CNT /Si Hybrid molar ratio of 0.05%, to the two matrices BPO0.01 and BPO0.05.…”

“…It is important to note that most as-synthesized CNTs consist of large aggregates or bundles insoluble both in water and in common organic solvents because of their enhanced polarizability induced by their cylindrical shape and hence the strong van der Waals' interactions between individual nanotubes [17]. Efficient dispersion of CNTs in a polymer matrix requires the initial disentanglement of these large aggregates and chemical compatibility between the CNTs and the polymer matrix to maintain a homogeneous and stable composite structure.…”