Thermodynamic theory of surface tension in solutions of linear polymer homologues

Differential equations for the surface tension as a function of temperature, pressure, and composition of a two-phase system containing linear macromolecules are derived within the framework of the quasi-solution theory. An alternative version of the theory has been developed for concentrated solutions and melts, in which the units and end groups are considered to be mobile components. Analysis shows that the existence of selective adsorption of chain units or end groups in the surface layer cannot be established simply on the basis of data on the surface tension in an homologous series. The feasibility of observing this hypothetical effect in measurements on the equilibrium elasticity of thick films of liquid polymer homologues is discussed.