Plasmonic Sensing of Heat Transport at Solid-Liquid Interfaces

We report experimental studies of interfacial heat transport for a system of Au nanodisks supported on fused silica substrates, coated by hydrophilic and hydrophobic self-assembled monolayers, and immersed in water-ethanol mixtures and solutions of a nonionic surfactant, hexyl-β-d-glucoside in water. The Au nanodisks are abruptly heated by a sub-picosecond optical pulse; time-resolved changes in the temperature of the Au nanodisk and the liquid near the nanodisk/liquid interface are monitored by measurements of transient changes in optical transmission. The interface thermal conductance G of nanodisks coated with a hydrophilic self-assembled monolayer (SAM) of sodium 3-mercapto-1-propanesulfonate varies over the range 90 < G < 190 MW m^-2 K^-1 as the composition of the liquid mixture is changed from pure ethanol to pure water. With increasing hexyl-β-d-glucoside concentration in water, the interface thermal conductance of hydrophilic nanodisks decreases from 190 MW m^-2 K^-1 to 130 MW m^-2 K^-1 as the concentration is varied between pure water and 100 mM glucoside. For hydrophobic surfaces, G = 70 ± 10 MW m^-2 K^-1. We relate changes in thermal conductance to changes in work of adhesion.