Light-induced quantum friction of carbon nanotubes in water

Abstract

Quantum friction describes the transfer of energy and momentum from electronically excited states in a material to a surrounding solvent. Here, we show that near-infrared (NIR) fluorescent single-walled carbon nanotubes (SWCNTs) exhibit quantum friction in water. The diffusion constants of functionalized SWCNTs in aqueous solution decrease linearly by around 50 % with increasing excitation power. In contrast, SWCNTs with quantum defects that localize excitons show no power-dependent diffusion. Chemical manipulation of exciton concentration by molecules that increase or decrease SWCNT fluorescence also modulate the diffusion constant by a factor of up to 2. Additionally, excitons increase the macroscopic viscosity of SWCNT solutions. Optical pump Terahertz (THz) probe spectroscopy reveals transient absorption features of water (37 /cm and above 80 /cm), indicating energy dissipation into translational modes of its hydrogen bond network. Molecular dynamics simulations further support a mechanism in which exciton-induced dipoles enhance frictional forces. These findings establish that excitons in SWCNTs induce quantum friction in water.