The Third Virial Coefficient in Polymer Solutions

With the aid of approximate models for the intermolecular potential energy, the third virial coefficient Γ3 in the virial expansion for the osmotic pressure of a dilute polymer solution has been determined as a function of the second coefficient and one additional parameter obtainable from intrinsic viscosity or light scattering measurements. The theory and experimental results agree in indicating that the ratio Γ3/Γ22 for most solutions is markedly less than the value of ⅝ given by the hard sphere molecular model proposed by others for the estimation of Γ3. The limitations are discussed under which light scattering may be used for evaluation of the virial coefficients.