Lyotropic liquid crystals of tetradecyldimethylaminoxide in water and the in situ formation of gold nanomaterials

Lyotropic liquid crystals(LLCs)produced by the self-assembly of surfactant in water represent an important class of highly ordered soft materials that have a wide range of applications.This study investigates the LLCs formed by a zwitterionic surfactant(tetradecyldimethylaminoxide,C 14 DMAO)in water.The organization of C 14 DMAO within the LLCs was determined based on a detailed analysis of small-angle X-ray scattering measure-ments and polarized microscopy observations of a typical sample.Additional to the singe-phase region,which has a hexagonal organization,several two-phase regions were observed,exhibiting the coexistence of hexago-nal/cubic,cubic/lamellar,and hexagonal/lamellar phases.The phase behavior showed an obvious dependence on temperature,with more pronounced two-phase regions at lower temperatures.Using the LLCs as a matrix,Au nanospheres,nanoellipsoids,and nanorods were prepared without requiring additional reducing reagents.These three-and one-dimensional Au nanomaterials could be converted to two-dimensional plates via the introduc-tion of a small amount of cationic surfactant to the LLCs,such as cetyltrimethylammonium bromide(CTAB)and 1-hexadecyl-3-methylimidazolium bromide([C 16 MIm]B),which showed pronounced surface-enhanced Raman scattering activity towards solid rhodamine.The LLCs loaded with CTAB(or[C 16 MIm]B)and HAuCl 4 exhibited slightly different structures and mechanical strength from the original LLCs,thereby forming a new class of highly crowded colloidal materials.