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If a liquid is in a container, then besides the liquid/air interface at its top surface, there is also an interface between the liquid and the walls of the container. The surface tension between the liquid and air is usually different (greater) than its surface tension with the walls of a container.
This assumption is approximately fulfilled for most known liquids. When plotting the surface tension versus the temperature a fairly straight line can be seen which has a surface tension of zero at the critical temperature. The Eötvös rule also gives a relation of the surface tension behaviour of different liquids in respect to each other: 2.
When a tube of a narrow bore, often called a capillary tube, is dipped into a liquid and the liquid wets the tube (with zero contact angle), the liquid surface inside the tube forms a concave meniscus, which is a virtually spherical surface having the same radius, r, as the inside of the tube. The tube experiences a downward force of magnitude ...
The capillary length will vary for different liquids and different conditions. Here is a picture of a water droplet on a lotus leaf. If the temperature is 20 o then = 2.71mm . The capillary length or capillary constant is a length scaling factor that relates gravity and surface tension.
During this process, surface tension decrease as function of time and finally approach the equilibrium surface tension (σ equilibrium). [3] Such a process is illustrated in figure 1. (Image was reproduced from reference) [2] Figure 1: Migration of surfactant molecules and change of surface tension (σ t1 > σ t2 > σ equilibrium).
Even though this relationship is empirical and less precise than the surface tension of a homologous series of liquids, it is very useful considering it is a parameter of the solid surface. This method is especially used to compare and measure the critical surface tension of low-energy solids (mainly plastics) very quickly and easily.
A practical implication of surface tension is that liquids tend to minimize their surface area, forming spherical drops and bubbles unless other constraints are present. Surface tension is responsible for a range of other phenomena as well, including surface waves, capillary action, wetting, and ripples.
Thus, he was able to establish a linear function between cos θ and the surface tension (γ LV) for various organic liquids. A surface is more wettable when γ LV and θ is low. Zisman termed the intercept of these lines when cos θ = 1 as the critical surface tension (γ c) of that surface. This critical surface tension is an important ...