Structural effects of water clusters on transport phenomena at high shear rates

Under high shear rate, shear viscosity of liquid water shows a decrease at growing shear rates. On the molecular scale, shear thinning correlates with significant structural arrangement of hydrogen bond network. It is essential to explore structural basis of shear thinning in liquid water.

We investigate shear-rate dependence of the viscosity of liquid water which occur ubiquitously at very large shear rates using molecular dynamics simulations. We construct quasi Carreau models to provide insight into the correlation between clustering and viscosity. Sufficient strong shearing can reduce the connectivity of hydrogen bonds. Structural responses along the compression and expansion axes of shear distortion respectively lead to the destruction or formation of hydrogen bonds.

Water clusters are crucial components to describe structural characteristics. Shear effects destroy large clusters into small clusters. To quantify the contribution from structures to water dynamics, we define hydrogen bond viscosity and cluster viscosity, which account for 10%-30% and 3%-25%, respectively, of total viscosity. We also observe a linear response of cluster distributions to viscosity, suggesting structural basis of water viscosity.

Our results explain structural origin of shear thinning in liquid water involving clusters and highlight the significance of cluster structures. The method can elucidate physical properties and form a bridge between macroscopic hydraulics and microscopic molecular dynamics.