Solid-Liquid Interaction and Capillary Effects
Phase transformations are discussed and the classical concepts of the Young, Laplace, and Kelvin equations are introduced. The role of the capillary effects at the nanoscale is further discussed including deviations from the conventional water phase diagr
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Abstract Phase transformations are discussed and the classical concepts of the Young, Laplace, and Kelvin equations are introduced. The role of the capillary effects at the nanoscale is further discussed including deviations from the conventional water phase diagram, stability issues associated with capillary effects, etc.
In the preceding chapters we studied multiscale dissipative mechanisms of solid– solid friction. In the second part of the book, we investigate the dissipative mechanisms of solid–liquid friction. In this chapter we introduce basic concepts of the physical chemistry relevant to the wetting of a solid surface by a liquid. We will emphasize the multiscale nature of mechanisms and interactions involved in the wetting process and specific nanoscale mechanisms of wetting.
5.1 Three Phase States of Matter It is well known that any substance can be in one of the three phase states: solid, liquid, or gas (vapor). There is also the fourth state, plasma; however, it is outside the scope of our consideration. Matter in the solid state has crystalline or amorphous structure with atoms or molecules packed closely together and strongly bonded to each other by the covalent, metallic, or ionic bonds. When examined at the macroscale, a solid body can sustain both compressive and tensile normal stresses and shear stress. With increasing temperature or decreasing pressure, a solid can melt and transform into the liquid state. In a liquid, polar molecules still have bonds (hydrogen or van der Waals) with each other, however, these bonds are weaker than the bonds in a solid, and they can be easily ruptured. At the macroscale, a liquid can sustain only normal isotropic stresses (usually compressive and rarely tensile), however, it flows when a shear stress is applied. Usually, molecules of a liquid are packed less closely than those of a solid, so the solid is denser than the liquid. A notorious exception is water, which at 0 ◦ C is denser than ice. This property of water is known as the “water anomaly,” and because of it ice flows at the water surface.
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5 Solid–Liquid Interaction and Capillary Effects
With further increase of the temperature or decrease of the pressure, a liquid can transform into vapor (gas). The characteristic feature of a gas is that it tends to expand and occupy all available space. The density of a gas is much lower than that of liquid and solid. The distance between gas molecules is large, and it can be assumed in many cases that there is no interaction between the gas molecules, except for the hardcore repulsion during their collisions. The model of the “ideal gas” is based on this assumption [283, 6]. Transitions between solid, liquid, and vapor states are known as the “phase transitions of the first kind,” as opposed to the “phase transitions of the second kind.” In general, phase transitions are characterized by an abruptly increased (or decreased) order in the system. The phase transitions of the first kind are also characterized by a significant amount of energy consumed or released durin
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