New articles by Ph.D. student Brian Uthe & Prof. Matt Pelton

In a pair of articles published in the Journal of Physical Chemistry Letters, Brian Uthe, Dr. Pelton, and their collaborators at the University of Melbourne, Australia, have revealed the unique properties of ordinary liquids at the nanometer scale. Various assumptions are made nearly universally to describe the flow of simple liquids such as water. One key assumption is that the liquids are “Newtonian,” meaning that they do not support shear strains: when an object moves in the liquid, the response of the liquid is purely viscous. Another key assumption is the “no-slip” boundary condition, that the liquid immediately adjacent to the solid surface does not move relative to the surface. The authors showed that both assumptions break down at the nanometer scale: because the motion of nanoscale objects occurs on the same time scales as the relaxation of molecules in the liquids, the liquids have an elastic, or solid-like component to their response, and that slip with nanometer-scale characteristic lengths occurs at the solid-liquid interface. The two papers interrogate these effects by using ultrafast lasers to monitor the vibration of metal nanoparticles in simple liquids. In the first paper, the authors show that these two effects interact synergistically, with viscoelasticity enhancing nanometer-scale slip. In the second paper, the authors show quantitative agreement between experiments in which there is no slip, using highly spherical metal nanoparticles, and a recently developed theory for the viscoelastic flow of simple liquids.

Viscoelasticity Enhances Nanometer-Scale Slip in Gigahertz-Frequency Liquid Flows
Debadi Chakraborty, Brian Uthe, Edward W. Malachosky, Matthew Pelton, and John E. Sader
J. Phys. Chem. Lett. 2021, 12, 3449–3455.
https://pubs.acs.org/doi/full/10.1021/acs.jpclett.1c00600

Highly Spherical Nanoparticles Probe Gigahertz Viscoelastic Flows of Simple Liquids Without the No-Slip Condition
Brian Uthe, Jesse F. Collis, Mahyar Madadi, John E. Sader, and Matthew Pelton
J. Phys. Chem. Lett. 2021, 12, 4440–4446
https://pubs.acs.org/doi/full/10.1021/acs.jpclett.1c01013