Direct observation of self-assembled chain-like water structures in a nanoscopic water meniscus

Abstract

Sawtooth-like oscillatory forces generated by water molecules confined between two oxidized silicon surfaces were observed using a cantilever-based optical interfacial force microscope when the two surfaces approached each other in ambient environments. The humidity-dependent oscillatory amplitude and periodicity were 3-12 nN and 3-4 water diameters, respectively. Half of each period was matched with a freely jointed chain model, possibly suggesting that the confined water behaved like a bundle of water chains. The analysis also indicated that water molecules self-assembled to form chain-like structures in a nanoscopic meniscus between two hydrophilic surfaces in air. From the friction force data measured simultaneously, the viscosity of the chain-like water was estimated to be between 10 8 and 10 10 times greater than that of bulk water. The suggested chain-like structure resolves many unexplained properties of confined water at the nanometer scale, thus dramatically improving the understanding of a variety of water systems in nature.

A fundamental mechanism for carbon-film lubricity identified by means of ab initio molecular dynamics

“…This result is in agreement with recent AFM measurements for undoped DLC films that exhibit high lubricity in the presence of adsorbed water. [10,23] We conclude the discussion with a comment on experimental observations that show an increase of friction in Si-DLC at high levels of humidity. [35,69] As stated above, a Si concentration of 5% has been proven to be sufficient to achieve low friction and the friction performance did not improve significantly by adding more Si dopants.…”

“…[9,20,21,22] In addition to the passivation, recent nano-scale experiments suggested another possible atomic mechanism to explain the extremely low friction of carbonbased film, which is connected to the presence of water molecules confined at the friction interface. [10,23,24,25] By means of atomic force microscope (AFM) measurements it has been uncovered the presence of an adsorbed water layer, few molecules thick, which may function as boundary lubricant on DLC films. [10] A friction force measurement showed that the viscosity of the confined water layer is more than 10 8 times greater than that of bulk water.…”

Contact Forces between Single Metal Oxide Nanoparticles in Gas-Phase Applications and Processes

“…Recent studies show that the structuring of water molecules and oscillating forces have to be considered for a correct description of water menisci on the scale of a few nanometer. 46−49 However, direct measurements of oscillating forces in a chain of nanoparticles using an AFM is very challenging because of the “jump-out” problem. When the applied force exceeds the spring constant of the cantilever the tip jumps away from the sample.…”

“…Using a stiffer tip would avoid this problem but decrease the sensitivity of the measurement. 46 Therefore, theoretical or computational approaches have to be used to analyze the details in the last peak ( F c ). Capillary, as well as solvation forces, strongly depend on the physisorbed water.…”

Colloidal crystals and water: Perspectives on liquid–solid nanoscale phenomena in wet particulate media

“…In particular, viscosity increases or relaxation/diffusion times decrease in several (up to 10) orders of magnitude under confinements below d ~ 1-2 nm due to gradual structuring of molecules near different surfaces, including amorphous silica [130,131,141−143]. The first 3-4 adsorbed water layers (d ~ 1 nm) even may adopt ice-like [94,130] or chain-like [143] structures and motion is practically hindered. From capillary filling experiments, an immobile water layer of 0.9 nm has been estimated [4].…”