Temperature effects contact angle

The effect of temperature on contact angle is seldom very great, as a practical observation. Some values of d0/dTare included in Table X-2 a common figure is about -0.1 degrees/K (but note the case of CS2 on ice also rather large temperature changes may occur in L1-L2-S systems (see Ref. 160). 

Thus apolar probe liquids of sufficiently high surface tension to yield finite contact angles against many surfaces are especially valuable for this purpose. Popular examples of these include diiodomethane, with a surface tension of 50.8 mN/m at 23°C, and a-bromonaphthalene, with a surface tension of 44.4 mN/m at the same temperature. One should be cautioned, however, that both are sufficiently volatile that the 7re-effects may not be negligible with their use. 

The effect of thermal aging on polyethylene and isotactic polypropylene have been studied by Konar et al. [49]. They used contact angle, contact angle hysteresis, and XPS to characterize the modified surfaces of the polymers. Hysteresis increased with aging temperature. In the case of polyethylene, thermal aging led to a significant increase in adhesion strength of polyethylene with aluminium, but the increase in the case of polypropylene was much less marked. 

Attempts to increase the contact angles of the diagnostic liquids by changing metal immersion conditions were not effective with the ethyl alcohol-water solutions. These attempts included (a) increasing the concentration of D by a factor of as much as four, (b) prolonging the immersion period from 1 to 64 hours, or (c) raising the temperature of immersion from 20°C. to 50°C. 

At high temperatures or in an atmosphere with a low P02, oxide films are often eliminated by dissolution in the metal, by thermodynamic decomposition or by formation of volatile sub-oxides. Even in these conditions, oxygen can still affect wettability, for instance by adsorption at metal/oxide interfaces. This effect leads to contact angles lower than the nominal contact angle of the inert system. Some examples of these oxygen effects are given in Section 6.4. Therefore, when contact... 

In the case of liquid Al, the solubility of oxygen is too low for a dissolution process to be effective. However, for other metals like Sn, it may be the principal mechanism. The variation in contact angle of Sn on AI2O3 shown in Figure 6.26 as a function of temperature displays three ranges. At low temperatures, high apparent... 

The process of expansion of an emulsion film is also quite similar to that of black spots in a foam film at low electrolyte concentrations the spots in the emulsion film expand slowly, at high concentrations the process is very fast (within a second or less) and ends up with the formation of a black film with large contact angle with the bulk phase (meniscus). In the process of transformation of the black spots into a black film, the emulsion film is very sensitive to any external effects (vibrations, temperature variations, etc.) in contrast to the equilibrium black foam film. 

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