Effects of adsorbed water layer structure on adhesion force of silicon oxide nanoasperity contact in humid ambient

Abstract

The origin of the large relative-humidity (RH) dependence of the adhesion force in the single-asperity contact between silicon oxide surfaces is elucidated. As RH increases, the adhesion force measured with an atomic force microscopy (AFM) initially increases, reaches a maximum, and then decreases at high RH. The capillary force alone cannot explain the observed magnitude of the RH dependence. The origin of the large RH dependence is due to the presence of an icelike structured water adsorbed at the silicon oxide surface at room temperature. A solid-adsorbate-solid model is developed calculating the contributions from capillary forces, van der Waals interactions, and the rupture of an ice-ice bridge at the center of the contact region. This model illustrates how the structure, thickness, and viscoelastic behavior of the adsorbed water layer influence the adhesion force of the silicon oxide nanoasperity contact.

The influence of humidity on the attachment ability of the spiderPhilodromus dispar(Araneae, Philodromidae)

“…On micro-rough surfaces, the amount of water must be high enough to span the asperities, so that a high RH (70 -99%) is necessary [26]. On a smooth hydrophilic SiO 2 surface, the water film already has liquid properties above 60 per cent RH [13]. Below that, the molecules in the water layer are composed in a solid-like manner.…”

“…They can come into play when there is a layer of water on the surface that is thick enough to build a liquid meniscus. For a smooth contact surface, such a critical thickness is supposed to be 0.7 nm [13,25]. The humidity of the air which is necessary to form such a water layer depends highly on physico-chemical properties of the substrate.…”

Nanoscale Fluorescence Microscopy Using Carbon Nanotubes

“…Alternatively, low phase values could simply indicate an increase in repulsive interactions upon nanotube penetration into the water layer. Finally, there has been a suggestion that the hydrogen bonding within ultrathin water layers can actually lead to icelike behavior [70], in which case, the repulsive interactions would be expected to increase. All of these explanations are more likely if the water layer is thin.…”

“…In fact, this water layer provides the mechanism needed for effective shear-force feedback widely used in aperture-type NSOM [71]. The specific structure of the water layer is not determined by the tip, but rather by the substrate, sample, temperature, and humidity [69], [70], [72]- [78]. Thus, when using an AFM probe without a nanotube, this width broadening would also be expected, assuming that the energy in the tip is low, i.e., small amplitudes.…”

Cantilever-Based Optical Interfacial Force Microscopy

“…The structured water exists not only on crystalline hydrophilic surfaces, but even on amorphous surfaces (Asay & S.H.J. Kim, , 2006Verdaguer et al, 2006). These studies indicate that the behavior of interfacial water molecules in an ambient environment is substantially different from the behavior of water at the liquid-solid interface.…”