Thermal Transport across Surfactant Layers on Gold Nanorods in Aqueous Solution

Ultrafast transient absorption experiments and molecular dynamics simulations are utilized to investigate the thermal transport between aqueous solutions and cetyltrimethylammonium bromide (CTAB)- or polyethylene glycol (PEG)-functionalized gold nanorods (GNRs). The transient absorption measurement data are interpreted with a multiscale heat diffusion model, which incorporates the interfacial thermal conductances predicted by molecular dynamics. According to our observations, the effective thermal conductance of the GNR/PEG/water system is higher than that of the GNR/CTAB/water system with a surfactant layer of the same length. We attribute the enhancement of thermal transport to the larger thermal conductance at the GNR/PEG interface as compared with that at the GNR/CTAB interface, in addition to the water penetration into the hydrophilic PEG layer. Our results highlight the role of the GNR/polymer thermal interfaces in designing biological and composite-based heat transfer applications of GNRs, and the importance of multiscale analysis in interpreting transient absorption data in systems consisting of low interfacial thermal conductances.