Hydrophilicity and the Viscosity of Interfacial Water

Abstract

We measure the viscosity of nanometer-thick water films at the interface with an amorphous silica surface. We obtain viscosity values from three different measurements: friction force in a water meniscus formed between an oxide-terminated W tip and the silica surface under ambient conditions; similar measurements for these interfaces under water; and the repulsive "drainage" force as the two surfaces approach at various speeds in water. In all three cases, we obtain effective viscosities that are approximately 10(6) times greater than that of bulk water for nanometer-scale interfacial separations. This enhanced viscosity is not observed when we degrade the hydrophilicity of the surface by terminating it with -H or -CH3. In view of recent results from other interfaces, we conclude that the criterion for the formation of a viscous interphase is the degree of hydrophilicity of the interfacial pair.

Cantilever-Based Optical Interfacial Force Microscopy

“…As an approach to study attractive regimes, friction forces have been measured using the IFM (Joyce & Houston, 1991), where the force feedback makes it possible. (Burns et al, 1999a;Goertz et al, 2007;Major et al, 2006). Burns et al applied IFM to measure friction force and normal force simultaneously to study the molecular nature of friction to investigate the intermolecular friction along with normal forces in the attractive regime (Burns et al, 1999a).…”

“…The tip-speed was controlled by the built-in digital-to-analog converter of the RHK controller in conjunction with the high-voltage amplifier. The lateral movement was achieved by dithering the sample in the long axis direction of the cantilever, using the piezo tube with an oscillatory signal of about 1 nm amplitude at the frequency of 100 Hz (Goddenhenrich et al, 1994;Goertz et al, 2007;Major et al, 2006). A Hewlett-Packard function generator (model 33120A) was used to generate the oscillatory signal.…”

“…The current AFM technique has been routinely applied to forced unbinding processes of biomolecular complexes such as antibody-antigen binding, ligand-receptor pairs, protein unfolding, DNA unbinding, and RNA unfolding studies (Butt et al, 2005;Fritz & Anselmetti, 1997;Schumakovitch et al, 2002). AFMs have also been applied to intermolecular friction studies (Carpick et al, 1997;Colchero et al, 1996;Fernandez-Torres et al, 2003;Goddenhenrich et al, 1994;Goertz et al, 2007; B.I. Kim et al, 2001;Major et al, 2006).…”

“…Kim et al, 2001;Major et al, 2006). These previous techniques of measuring friction employed a lateral modulation of the sample relative to the cantilever as a means to measure normal force and friction force at the same time (Burns et al, 1999a;Carpick et al, 1997;Colchero et al, 1996;Goddenhenrich et al, 1994;Goertz et al, 2007;Major et al, 2006). However, AFM usage has been limited to passive applications (e.g., pull-off force measurement in the force-distance curve) and can only be applied to the measurement of friction while the tip is touching the sample surface because of an intrinsic mechanical instability of the tip-sample assembly near a sample surface called the "snap-to-contact problem" (Burnham, 1989;Lodge, 1983).…”

From Microtornadoes to Facial Rejuvenation: Implication of Interfacial Water Layers

“…Hydrophilic conversion and reduction in polarity contrast due to the osmiophilic interlayer further encourages the encapsulation of the fibers by a viscous interfacial water layer (left). [3][4][5] water, we are justified in assuming that most of the mobile molecules surrounding the elastic fibers are water molecules. This picture leaves room for an energy minimizing argument, related to the possible organization of the interfacial water on elastic fibers performing their function: From previous work we concluded that crystalline water layers immobilized on hydrophobic substrates are instrumental in reducing dissipative effects at the solid-liquid interface during evaporative processes.…”