Phase behavior and shear alignment in SWNT-surfactant dispersions

Area of Science:

• Materials Science
• Physical Chemistry
• Colloid Science

Background:

• Cationic surfactants like cetyltrimethylammonium bromide (CTAB) form complex phases in aqueous solutions.
• Carbon nanomaterials, including single-walled carbon nanotubes (SWNTs), are increasingly used in various applications.
• Understanding the interaction between surfactants and carbon nanomaterials is crucial for developing new functional materials.

Purpose of the Study:

• To investigate the effect of single-walled carbon nanotubes (SWNTs) on the phase behavior of cetyltrimethylammonium bromide (CTAB) in aqueous solutions.
• To explore the influence of SWNTs on the structure of CTAB solutions and thin films under different conditions.
• To compare the effects of SWNTs with other carbonaceous additives.

Main Methods:

• Small-angle X-ray scattering (SAXS) for bulk dispersion characterization.
• Cryogenic transmission electron microscopy (cryo-TEM) for nanostructured film analysis.
• Systematic variation of surfactant concentration and use of reference carbonaceous additives.

Main Results:

• SWNTs induce demixing and phase separation in CTAB solutions at intermediate concentrations, forming two coexisting liquid phases.
• At high CTAB concentrations, SWNTs incorporate into the lyotropic liquid-crystalline phase without altering its native spacing.
• Shear-induced structure (SIS) in nanometrically thin CTAB films is observed exclusively with SWNTs, not with other carbon additives.

Conclusions:

• SWNTs significantly alter the phase behavior of CTAB solutions, leading to macroscopic phase separation.
• SWNTs can integrate into existing surfactant liquid-crystalline structures.
• The unique ability of SWNTs to induce shear-induced structure in thin films highlights their specific interactions with surfactant systems.