Abstract
Understanding the dynamics of liquids at the atomic level remains a major challenge. Even though viscosity is one of the most fundamental properties of liquids, its atomistic origin is not fully elucidated. Through inelastic neutron scattering experiment on levitated metallic liquid droplets, the time-dependent pair correlation function, the Van Hove function, was determined for Zr50Cu50 and Zr80Pt20 liquids at various temperatures. The time for change in local atomic connectivity, 𝜏𝐿𝐶, which is the timescale of atomic bond cutting and forming, is estimated based on the exponential decay of the nearest neighbor peak of the Van Hove function. At high temperatures above the crossover temperature 𝑇𝐴, 𝜏𝐿𝐶 is equal to the Maxwell relaxation time, 𝜏𝑀=𝜂/𝐺∞, where η is the macroscopic shear viscosity and 𝐺∞ is the high-frequency shear modulus. Below 𝑇𝐴 the ratio of 𝜏𝑀/𝜏𝐿𝐶 increases with decreasing temperature, indicating increased atomic cooperativity as predicted by molecular dynamics simulation.
