Search

Film-forming properties of polymer in aqueous solution flowing through a nanogap have been investigated by using a thin film interferometry. The film properties of linear polymer in aqueous solution flowing through a confined nanogap depend on the ratio of water film thickness to averaged radius of polymer chains H0/RPolymer. It was found that the lubrication film thickness of linear polymer in aqueous solution decreases as the polymer molecular weight increasing when H0/RPolymer < 2 ∼ 3. A new lubrication map was proposed, which includes the lubrication regime of weak confinement influence, the lubrication regime of strong confinement influence (LRSCI), and the transition regime of confinement influence. It is very difficult to increase the lubrication film thickness using the higher molecule weight in the LRSCI regime. The lubrication mechanism inferred from our experimental results may help to better understand the dynamic film properties of linear polymer in aqueous solution flowing through a nanogap. [ABSTRACT FROM AUTHOR]

A fluorescence microscope and a light microscope were employed to observe the phenomenon of water flowing toward an oil nanogap between two solid surfaces. It was found that water was able to displace hexadecane in the nanogap confinement, which contradicted previous viewpoints. An increase in water flow speed contributed to entrainment of water into the contact region, due to inadequate oil supply. Surface energy was found to be another factor that influenced the displacement phenomenon. It was easier for water to enter the contact region on the surface with a greater surface energy, since less energy is required to separate the contact of hexadecane and solid surface and to form water's own contact. [ABSTRACT FROM AUTHOR]

The influence of surface hydrophilicity on adsorbed water layer was investigated using a thin film interferometry and a microtribometer based on laser interferometers. Experimental results indicate that, in the mixed film lubrication from the boundary lubrication to the thin film lubrication, the hydrophilic surface promotes the forming of thinner water film and the higher friction. It is thought that a layer of water adjacent to the surface forms an ordered water layer whose characteristic determines the properties of adsorbed water layer in the contact area. [ABSTRACT FROM AUTHOR]

The effect of surface charge on the water film confined between hydrophilic solid surfaces has been investigated using thin film interferometry. Experimental results indicate that the higher surface charge density induces the thicker water film for model surfaces, silica, and alumina. It is thought that the strong surface field induced by the surface charge establishes a more ordered hydrogen-bonding network that promotes the forming of thicker water lubrication film between hydrophilic solid surfaces. [ABSTRACT FROM AUTHOR]

The effect of surface hydrophilicity on the water film confined within a nanogap between a smooth plate and a highly polished steel ball has been investigated. It was found that the confined water film formed the thicker lubricate film than the prediction of elastic-isoviscous lubrication theory. Experimental results indicated that the hydrophobic surface induced the thicker water film than the hydrophilic one. It is thought that the “structured” interfacial water layer is formed between the solid surfaces and the hydrophobic group induces the more ordered hydrogen-bonding network of clathrate cages which forms the thicker water film than hydrophilic one. [ABSTRACT FROM AUTHOR]

A counterintuitive phenomenon, 'boiling,' was directly observed near the contact line of the pure water meniscus formed in a ball and disk configuration, when the ball temperature was far lower than the saturation temperature of water. The number of the emerging bubbles due to 'boiling' increased with ball temperature rising; each bubble would expanse initially and then collapse. When two surfaces were heated to the same temperature, 'boiling' disappeared. It was proposed that the temperature gradient between the two surfaces initiated Marangoni flow, which hindered flow toward the film, resulting in the negative pressure and cavitation in the liquid film. [ABSTRACT FROM AUTHOR]