Tailoring self-assembly behavior of a biological surfactant by imidazolium-based surfactants with different lengths of hydrophobic alkyl tails

Abstract

In this work, the effects of four imidazolium-based surfactants with different lengths of hydrophobic alkyl tails ([C₂mim]Br, [C₈mim]Br, [C₁₂mim]Br, and [C₁₄mim]Br) on the self-assembly behaviors of the biological surfactant sodium deoxycholate (NaDC) in sodium phosphate buffer (pH = 7) were investigated systematically. The microstructures and properties of NaDC/C_nmimBr (n = 2, 8, 12, 14) mixed systems were characterized using transmission electron microscopy (TEM), field emission-scanning electron microscopy (FE-SEM), polarized optical microscopy (POM) observations, Fourier transform infrared (FT-IR), X-ray powder diffraction (XRD) and rheological measurements. The roles of the hydrophobic chain length, the chiral rigid steroid center, and the electrostatic interaction for the evolution of phase behavior are clearly described. The results indicated that the long-chain imidazolium-based surfactants ([C_nmim]Br, n ≥ 8) weakened the gel of NaDC, while C₂mimBr strengthened the gel behavior of NaDC and even can form microcrystals. The super-hydrogels formed by these systems may act as promising adsorbents for the removal of heavy-metal ions from industrial sewage.