Effect of Capping Molecules on Liquid Slip at the Surfaces of Vibrating Gold Nanoparticles

Abstract

Transient absorption (TA) measurements on vibrating metal nanoparticles suspended in solution offer a noncontact method for monitoring solid–liquid interfacial phenomena on the nanoscale and at ultrafast time scales. Here, we use this method to investigate the effect of capping molecules on the liquid slip at the surface of gold nanoparticles. In particular, we functionalize both bipyramidal and spherical gold nanoparticles with a series of capping molecules and use TA measurements to monitor the oscillations in plasmon resonance frequency as a function of time after excitation by a pump laser pulse. Analysis of the Fourier transform of these oscillations and comparison to theory reveal slip lengths that vary by nearly a factor of 3 for different capping molecules, even though the molecules have similar chemical end groups. Moreover, there is no clear relationship between the measured slip length and macroscopic measurements of surface wettability. The results indicate that nanoscale slip at high frequencies might depend more subtly on the detailed molecular arrangement between ligand and solvent molecules.