CTAB promoted synthesis of Au nanorods--temperature effects and stability considerations.

A systematic study is performed of the influence of surfactant and temperature on the aspect ratio and monodispersity of Au nanorods, synthesized by a seed-mediated growth technique in water using cetyltrimethylammonium bromide (CTAB) as surfactant. The changes in aspect ratio with temperature show an "anomalous" behavior, where the aspect ratio first decreases with increasing temperature, reaching a minimum at about 55 degrees C, and after that increases again reaching a maximum at about 80 degrees C. A physical explanation of the observed behavior is proposed. It has also been studied how the CTAB concentration in the cleansing water used in the post-synthesis treatment of the samples affected the stability of the gold suspension. It was found that without the presence of a surfactant such as CTAB in the washing medium, only very few centrifugations can be carried out without considerable loss of product. Characterization of prepared samples was performed with UV-Vis and TEM.