Development of novel anionic Gemini surfactants and application in fabricating hierarchical silver microparticles for surface-enhanced Raman spectroscopy.

In this work, a new category of anionic Gemini surfactants with a rigid space, disodium 2,2'-(1, 4-phenylene bis (methylene)) bis (alkane-1-sulfate) (Cm ArCm , m=8, 10, 12, 14), were developed. They showed excellent surface activity and remarkable micellization tendency in aqueous solutions as measured by the equilibrium surface tension method. It was noticed that both the surface activity and micellization ability of Cm ArCm were gradually strengthened upon increasing the hydrophobic chain length m. Those Gemini surfactants were employed as capping reagents to fabricate three-dimensional (3D) hierarchical silver microparticles (AgMPs) successfully even in a large-scale of gram-level. The morphological evolution of these microparticles in different conditions was investigated systematically by various techniques including scanning electron microscopy (SEM), high-resolution transmission electron microscope (HRTEM), powder X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The possible formation mechanism of surfactant assisted AgMPs was also proposed. It was found that the morphology of AgMPs could be tailored from nut-like, lichi-like, to coral-like microparticles by simply varying the concentration of surfactant. However, the hydrophobic chain length m of Cm ArCm showed a little influence on the morphology of AgMPs. Moreover, the surface-enhanced Raman scattering of Rhodamine 6G results evidently confirmed the superior surface activity of synthesized AgMPs.