Surface tension frictional forces

The fundamental principle of Hquid disiategration Hes ia the balance between dismptive and cohesive forces. The common dismptive forces ia atomizer systems iaclude kinetic energy, turbulent fluctuation, pressure fluctuation, iaterface shearing, friction, and gravity. The cohesive forces within the Hquid are molecular bonding, viscosity, and surface tension. 

The developed theory of two-phase laminar flow with a distinct interface which is based on a one-dimensional approximation, takes into account the major features of the process the inertia, gravity, surface tension and friction forces and leads to the physically realistic pattern of a laminar flow in a heated micro-channel. This allows one to use the present theory to study the regimes of flow as well as optimizing a cooling system of electronic devices with high power densities. 

A qualitative model for lubrication of the condensed alcohol layer is not fully developed yet. We present here the best qualitative model based on the literature. As the applied pressure is very large and the scanning speed is very low in AFM, one can rule out the hydrodynamic lubrication even in the presence of condensed alcohol layer on the substrate. The AFM tip and substrate interface must be in the boundary lubrication regime. Figs. 7-10 show that the adhesion force reduction upon alcohol adsorption is accompanied by reduction of the friction force. Part of the adhesion force reduction is because of the surface tension decrease of the water layer on the substrate. When alcohol is dissolved in water, the surface tension decreases significantly because of segregation of alcohol molecules to the liquid-air interface. ... 

At the millimetre scale, gravity, friction, combustion and electrostatic forces predominate. At the micrometer scale, it is mainly electrostatic forces, van der Waals forces and Brownian motion that are at work. Forces related to volume, like weight and inertia, tend to decrease in significance while forces related to surface area, such as friction and electrostatics, tend to increase in significance. Surface tension, which depends upon an edge, and viscosity both become very significant and impact hugely on the movement of liquids as discussed in the previous section. Hence, sometimes these processes can aid the development of chip-based devices while in other cases they present limitations. 

In this expression Y = Yi + Y2 12 where Yj and Y2 are the surface tensions of the sphere and flat, respectively, and Yj2 is the surface tension of the interface between them. The JKR expression recognizes the fact that even in the absence of a normal force (N = 0) siuface tension will cause some elastic deformation of the surfaces producing a finite contact area. This fact alone renders the concept of a coefficient of friction meaningless since it implies that there is some finite friction force between solids even under zero normal force. 

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