Critical surface tension temperature effect

One can obtain a relationship (Eq. (2.11)) between the critical surface tension and the solid-vapor surface tension by setting the contact angle to 0 in Young s equation (Eq. (2.6)). Therefore, critical surface tension is smaller than solid-vapor surface tension. Figure 2.7 shows the effect of temperature on the critical surface tension of two plastics. The surface energy of plastics decreases with temperature. 

Figure 2.7 Effect of temperature on critical surface tension of two plastics.t ...

Fig. 13. Effect of temperature on the critical surface tension of a low-energy solid (y, open circles Yes fiHad circles) and a comparison with the effect of temperature on the surface tension of a chemically related liquid.

Fig. 14. Effect of temperature on the critical surface tension for spreading on low-energy surfaces (A) poly(ethylene terephthalate) (B) polyoxymethylene (C) polyethylene (D) polycarbonate (E) polystyrene (F) silicone (G) and (H) polytetrafluoroethylene and (J) and (K) polytetrafluoroethylene-hexafluoropropylene copolymer.

Figure 1 determines the foregoing temperature effect and is easier to use than the equation or a nomograph proposed by Kharbanda for this relation. The results are fairly accurate, provided the temperatures for which the surface tensions are considered are not close to the critical temperature of the material in question. Best results are obtained for nonpolar compounds. 

Physical characteristics Molecular weight Vapour density Specific gravity Melting point Boiling point Solubility/miscibility with water Viscosity Particle size size distribution Eoaming/emulsification characteristics Critical temperature/pressure Expansion coefficient Surface tension Joule-Thompson effect Caking properties... 

B. The critical pressure of a liquid is its vapor pressure at the critical temperature and is always a constant value. A rising temperature increases the kinetic energy of molecules and decreases the importance of intermolecular attraction. More molecules will be free to escape to the vapor phase (vapor pressure increases), but the effect of attractions at the liquid-gas interface will fall (surface tension decreases) and molecules will flow against each other more easily (viscosity decreases). 

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