Application of Extended Scaling Law to the Surface Tension of Fluids of Wide Range of Molecular Shapes

Abstract

A linear correlation is presented between the reduced surface tension \sigma^* and reduced temperature T^*_{extScal} by applying the extended scaling law. The correlation is applied quite accurately to 17 atomic, diatomic, and molecular fluid hydrocarbons of wide range of molecular shapes. The reduced surface entropy S^{s^*}_{extScal} is introduced, which has a value of 1.000 over the whole liquid range, indicating that the corresponding states principle is followed fully. The correlation for S^{s^*}_{extScal} contains a quantity E^s_\mu, which is related to the surface energy E^s, in the form E^s_\mu = [\sigma - (1/\mu)T(d\sigma/dT)], where \sigma is the surface tension, T is the absolute temperature, miu is the critical exponent for surface tension, and the surface entropy S^s=-(d\sigma/dT). E^s_\mu is different from Es by an additional (1/\mu) factor coupled to S^s. The form of the equation of E^s_\mu is different from the equation of E^s, which is a combination of the first and the second laws of thermodynamic for interface. The relation for S^{s^*}_{extScal} acts as an intermediate equation to derive a new analytical expression for E^s_\mu in terms of intensive physical and thermodynamic properties of the particular fluid. Key words: Critical exponent; Extended scaling; Law of corresponding states; Surface energy; Correlation for Surface tension;