Thermal instability of gold nanorods in micellar solution of water/glycerol mixtures

Gold nanorods (Nds) with aspect ratios of L/d (length divided width) = 4, 3.5 and 2.8 with absorption maxima at 810, 750 and 680 nm, respectively, encapsulated in micelles were prepared by electrochemical method. The nanorods were studied in binary solvents of aqueous glycerol water at different ratio (25–75%) and different temperatures (35–100 °C). The results showed that, the longitudinal surface plasmon resonance (SPL) is strongly dependent on the dielectric constants and temperatures. On the other side, for the gold nanorods with an average aspect ratio of (L/d = 4), the results obtained illustrated that the main aspect ratio of the nanorods in 75% of glycerol/water ratio (v/v) decreases with increasing temperature due to the relative instability of the micelles capping the longer gold nanorods. TEM showed that no significant changes in the width of the nanorods occurs upon increasing the temperature. The activation energy of thermal reshaping of gold nanorods in the temperature range 60–100 °C was found to be 12.9 ± 1 kcal/mol and the rate constants increase from 6 × 10−5 to 2.1 × 10−4 s−1 upon increasing the temperature from 333 to 373 K−1. The craft (dissolution) temperature of the nanorods in 75% of glycerol/water micellar medium was determined as ∼130 °C.