Fluid Dynamic Properties of Nanoconfined Water

Abstract

Most of the nano-metric confined space is filled with liquid water called nanoconfined water in ambient condition, to say nothing of liquid water enviroment. The ubiquitous nanoconfined water naturally plays an important role for various mechanisms such as biological processes, swelling clays, colloidal interaction, and friction. In the 21st Century, the study of the nanoconfined water has begun in earnest due to the development of techniques to control stable nanoconfined space in ambient or liquid condition. Meanwhile reported properties of nanoconfiend water are summarized as follows. (i) enhanced viscosity 10^2~10^7 times larger compared with bulk water, (ii) sluggish relaxation time (10^-2 ~ 10^-9 s), (iii) nonlinear viscoelasticity, and (iv) violence of classic interfacial force. Although the various properties have been phenomenologically known, however, (1) the fundamental understanding of characteristics or the understanding of the relation between properties are still insufficient. And, (2) until now, the slow velocity (<~10^-6 m/s) experiments are performed only even though more fast-velocity friction frequently occurs in nature.

In this study, (1) the unified stress tensor of nanoconfined hydration water layer (HWL), which shows the relation between characteristics of HWL and leads the other physical quantities by relation between tapping and shear properties, is introduced and demonstrated using quartz tuning fork based atomic force microscopy (QTF-AFM). And, (2) through fast velocity ( ~1 mm/s) experiments, the nanoscale elastic turbulence, which is marvelous phenomenon since it is impossible in Newtonian flow, is observed. Moreover the autoregulation in capillary, which is phenomenon that blood flow velocity is maintained automatically despite of a blood pressure change, may be understood through the nanoscale elastic turbulence between red blood cell and capillary wall.

The study about unified stress tensor would contribute not alone nanoconfined water but methodology of various viscoelastic material studies. And elastic turbulence in nanoconfined water would be considered in various fields where nanoconfiend water exists. In particular, the physical understainding of autoregulation in capillary is anticipated to expand understanding of brain science such as cerebral infarction or Alzheimer's disease.