Shear-stress function approach of hydration layer based on the Green-Kubo formula

Kim, Bongsu; Kwon, Soyoung; Moon, Geol; Jhe, Wonho

doi:10.1103/physreve.91.032307

Cited by 2 publications

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“…S3A (SI Appendix, section S4). Simulations on HWL between adjacent hydrophilic surfaces, which are interrelated by the hydrogen-bond network, show that (24) the correlation time between hydrogen bonds becomes longer than in bulk water, as observed (19)(20)(21) or expected (22) by the sluggish dynamics with a longer τ (Fig. 2B).…”

Section: Significancementioning

confidence: 99%

“…The hydration water layer (HWL), which is a ubiquitous form of nanoscale water consisting of water molecules tightly bound to ions or hydrophilic surfaces, is a highly viscoelastic fluid showing sluggish relaxation time (19)(20)(21) up to 10 μs (22). Better understanding of the HWL dynamics, especially its nonlinear rheology, is increasingly on demand to address diverse processes associated with HWL and to develop related technologies (23,24).…”

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Probing nonlinear rheology layer-by-layer in interfacial hydration water

Kim

Kwon

Lee

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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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, elasticityassociated 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.nonlinear rheology | hydration layer | shear thickening | elastic turbulence | dynamic force spectroscopy T he rheological nonlinearity of fluids (1-3) is a universal, highly nonequilibrium phenomenon observed in diverse systems ranging from soft materials [e.g., polymeric (1, 4), biological (5, 6), and colloidal (2, 7-9) solution] to terrestrial layers [e.g., Earth's mantle (10)], occurring at extremely high shear rates (1, 2, 11). Although shear thinning (decrease of viscosity) originates from the decrease of particle density correlation (2, 12), shear thickening (4, 7, 8, 13-17) (increase of viscosity) has been understood in various perspectives such as hydrodynamic instability (18) at high Reynolds number (Re) or order-disorder transition (13,14) at low Re and high Weissenberg number (Wi) [a measure of elasticity of viscoelastic flows (1); see SI Appendix, section S1, for nonlinear hydrodynamics formalism based on Re and Wi]. In particular, such a viscoelastic flow with low Re and high Wi exhibits behaviors similar to the inertial turbulence of Newtonian flow, so termed the elastic turbulence (4, 17). Despite extensive studies, however, one still lacks understanding of (i) the role of elastic instability in the enhanced flow resistance and (ii) the unexplored characteristics of nonlinear rheology at nanoscale.The hydration water layer (HWL), which is a ubiquitous form of nanoscale water consisting of water molecules tightly bound to ions or hydrophilic surfaces, is a highly viscoelastic fluid showing sluggish relaxation time (19-21) up to 10 μs (22). Better understanding of the HWL dynamics, especially its nonlinear rheology, is increasingly on demand to address diverse processes associated with HWL and to develop related technologies ...

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