Molecular-Scale Density Oscillations in Water Adjacent to a Mica Surface

Abstract

High-resolution specular x-ray reflectivity of the mica(001)-water interface under ambient conditions reveals oscillations in water oxygen density in the surface-normal direction, giving evidence of interfacial water ordering. The spacings between neighboring water layers in the near-surface, strongly oscillatory region are 2.5(2)-2.7(2) A, approximately the size of the water molecule. The density oscillations extend to about 10 A above the surface and do not strictly maintain a solvent-size periodicity as that in interfacial liquid metal and hard-sphere molecular liquids. We interpret this oscillatory density profile of the interfacial water as due to the "hard-wall" effect of the molecularly smooth mica surface.

Squeeze-out dynamics of nanoconfined water: A detailed nanomechanical study

“…The picture that emerges from these studies matches well with previous experimental and computational studies. In particular, by using a direct measurement of the nanomechanics of the system, we confirm the existence of the adsorbed water layer on mica surface as suggestedby earlier studies [29,30]. By analyzing the data using two different viscoelastic models, using improved data analysis methods to determine the true tipsurface separation, and determining the film stiffness in two distinct ways, we reconstructed the overall dynamics and viscoelastic response as a hydration layer is rapidly compressed and expelled between two approaching hydrophilic surfaces.…”

Advanced Instrumentation of Frequency Modulation AFM for Subnanometer-Scale 2D/3D Measurements at Solid-Liquid Interfaces

“…Therefore, the results obtained in this study support the model proposed by Cheng et al [93], where the adsorbed and laterally-distributed water molecules coexists at the interface. The co-existence of water molecules having a long relaxation time (adsorbed water) and laterally-distributed disordered water molecules (2D hydration layer) may reconcile the two opposing ideas of "ice-like" and "liquid-like" water molecules at the mica-water interface.…”

“…In addition, owing to the ease of cleavage to present an atomically flat surface, mica-water interface has been widely used as a model system to investigate nanofluidics in engineering and physics [87], lubrication in tribology, and molecular adsorption and diffusion in biology and chemistry. To date, water distribution at mica-water interface has been extensively studied by various techniques [88][89][90][91][92][93][94]. However, its atomistic model has not been established due to the difficulties in visualizing molecular-scale water distribution directly at a solid-liquid interface.…”

“…Recently, studies using x-ray reflectome-try [93] and Monte Carlo simulation [94] consistently suggested the existence of adsorbed water molecules presenting localized water distribution above OH groups in addition to the laterally distributed hydration layer. The water density profiles obtained in these previous studies revealed the Z distance between the peaks corresponding to the hydration layer and adsorbed water molecules is 0.12 nm.…”

Liquid ordering at the Brushite-{010}–water interface

“…Huisman et al 4 found evidence for layering of liquid gallium in contact with a diamond surface using x-ray diffraction. Recently Cheng et al 5 found molecular-scale density oscillation at the water/ mica interface using specular reflectivity.…”