Rapid onset of molecular friction in liquids bridging between the atomistic and hydrodynamic pictures

  • Friction in liquids arises from conservative forces between molecules and atoms. Although the hydrodynamics at the nanoscale is subject of intense research and despite the enormous interest in the non-Markovian dynamics of single molecules and solutes, the onset of friction from the atomistic scale so far could not be demonstrated. Here, we fill this gap based on frequency-resolved friction data from high-precision simulations of three prototypical liquids, including water. Combining with theory, we show that friction in liquids emerges abruptly at a characteristic frequency, beyond which viscous liquids appear as non-dissipative, elastic solids. Concomitantly, the molecules experience Brownian forces that display persistent correlations. A critical test of the generalised Stokes–Einstein relation, mapping the friction of single molecules to the visco-elastic response of the macroscopic sample, disproves the relation for Newtonian fluids, but substantiates it exemplarily for water and a moderately supercooled liquid. The employed approach is suitable to yield insights into vitrification mechanisms and the intriguing mechanical properties of soft materials.
Author:Arthur V. StraubeORCiD, Bartosz G. Kowalik, Roland R. Netz, Felix HöflingORCiD
Document Type:Article
Parent Title (English):Commun. Phys.
First Page:126
Date of first Publication:2020/07/10
Licence (German):License LogoCreative Commons - CC BY - Namensnennung 4.0 International