title: Probing nonlinear rheology layer-by-layer in interfacial hydration water.
abstract: Viscoelastic fluids exhibit rheological nonlinearity at a high shear rate. Although typical nonlinear effects, shear thinning and shear thickening, have been usually understood by variation of intrinsic quantities such as viscosity, one still requires a better understanding of the microscopic origins, currently under debate, especially on the shear-thickening mechanism. We present accurate measurements of shear stress in the bound hydration water layer using noncontact dynamic force microscopy. We find shear thickening occurs above ∼ 10(6) s(-1) shear rate beyond 0.3-nm layer thickness, which is attributed to the nonviscous, elasticity-associated fluidic instability via fluctuation correlation. Such a nonlinear fluidic transition is observed due to the long relaxation time (∼ 10(-6) s) of water available in the nanoconfined hydration layer, which indicates the onset of elastic turbulence at nanoscale, elucidating the interplay between relaxation and shear motion, which also indicates the onset of elastic turbulence at nanoscale above a universal shear velocity of ∼ 1 mm/s. This extensive layer-by-layer control paves the way for fundamental studies of nonlinear nanorheology and nanoscale hydrodynamics, as well as provides novel insights on viscoelastic dynamics of interfacial water.
authors.affiliation: Department of Physics and Astronomy, Institute of Applied Physics, Seoul National University, Seoul 151-747, Republic of Korea.
authors.forename: Bongsu
authors.initials: B
authors.lastname: Kim
authors.affiliation: Department of Physics and Astronomy, Institute of Applied Physics, Seoul National University, Seoul 151-747, Republic of Korea.
authors.forename: Soyoung
authors.initials: S
authors.lastname: Kwon
authors.affiliation: Department of Physics and Astronomy, Institute of Applied Physics, Seoul National University, Seoul 151-747, Republic of Korea.
authors.forename: Manhee
authors.initials: M
authors.lastname: Lee
authors.affiliation: Department of Physics and Astronomy, Institute of Applied Physics, Seoul National University, Seoul 151-747, Republic of Korea.
authors.forename: Q Hwan
authors.initials: QH
authors.lastname: Kim
authors.affiliation: Department of Physics and Astronomy, Institute of Applied Physics, Seoul National University, Seoul 151-747, Republic of Korea.
authors.forename: Sangmin
authors.initials: S
authors.lastname: An
authors.affiliation: Department of Physics and Astronomy, Institute of Applied Physics, Seoul National University, Seoul 151-747, Republic of Korea whjhe@snu.ac.kr.
authors.forename: Wonho
authors.initials: W
authors.lastname: Jhe
keywords: dynamic force spectroscopy; elastic turbulence; hydration layer; nonlinear rheology; shear thickening