Typical Surface Tension Data of Liquids

At this stage, it is important to consider how the magnitude of surface tension of different molecules changes with respect to the molecular structure (Table 1.2). Extensive studies are found that attempt to correlate surface tension to other physicochemical properties of liquids, such as boiling point, heat of evaporation, etc. This concept has been extensively analyzed in the literature (Birdi, 2010a Jasper, 1972). In research and other applications where the surface tension of Uqnids plays an important role, it is necessary to be able to predict the magnitude of y of different kinds of molecules. 

These data need some comments in order to explain the differences in snrface tension data and molecular structure. The range of y is found to vary from ca. 20 to ovct 1000 mN/m. The surface tension of Hg is high (425 mN/m), for example, as compared to that of water, because it is a liquid metal with a very high boiling point. Latter indicates that it needs much energy to break the bonds between Hg atoms to evaporate. Similarly, y of NaCl as a liquid (at high temperature) is also very high (Table 1.2). The same is found for metals in liquid state. The other liquids can be considered as under each type, which shonld help understand the relation between the structure of a molecule and its surface tension. 

It is usefnl to consider some data (Jasper, 1972) that will provide information about structure and surface tension relationship in some simple liquids. 

Alkanes (normal) It is found that the magnitude of y (at 25°C) increases by 1.52 mN/m per two -CHj, when alkyl chain length increases from 10 to 12 (n-decane = 23.83 mN/m n-dodecane = 25.35 mN/m). 

These observations indicate the molecular correlation between bnlk forces and surface forces (tension) (y) for homologons series of substances. 

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