| Abstract
| - Gold nanorods are prepared in aqueous solution by an electrochemical method and are shape controlled byusing capping micelles as described by Yu et al. (J.Phys.Chem.B1997, 101 (34), 6661). Transmissionelectron microscopic (TEM) images are determined for these gold nanorods, taken from solutions heated tovarious temperatures in the range of 25−160 °C. Size and shape analysis of their TEM images showed thatthe mean aspect ratio of the nanorods in solution decreases with increasing temperature, mostly as a result ofreduction in their length. Heating the dried nanorods themselves on a TEM slide to much higher temperaturesdoes not produce any shape changes. This suggests that the observed relative instability of the longer nanorodsin the micellar solutions is attributed to the relative instability of the micelles capping the longer gold nanorods.Following the change with time of the longitudinal surface plasmon absorption band of the gold nanorods atfive different temperatures, the activation energy for the thermal decomposition of the micelles is found to be21.0 ± 1.0 K cal mol-1. The most stable rod-shaped micelle is found to have an aspect ratio of 2.0. Thecraft decomposition (dissolution) temperature of these micelles is found to be ∼155 °C. This study offers anew method in which the thermal stability of micelles of various shapes is used to change the size distributionof metal nanorods in solution. On the other hand, TEM or the absorption maximum of the longitudinalplasmon resonance of gold nanorods can be used as a sensitive monitor in studying the physical propertiesof the host micelles themselves.
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