A theory of the thermodynamic behavior of nonelectrolyte solutions. V. The scattering of light by polymer solutions

Maron's theory of the thermodynamics of non‐electrolyte solutions has been used to examine the light scattering behavior of both dilute and concentrated solutions of polystyrene in several solvents. It is shown that for each polymer‐solvent system at a given temperature the behavior can be characterized, as in the case of osmotic pressure, by a single interaction parameter μ which varies linearly with volume fraction v 2 , i.e. μ=μ ° +σ ° v 2 , where μ ° and σ ° are constants. Introduction of this equation into Maron's theory leads to functional plots in dilute solutions which are linear even when the conventional plots of HC/τ versus C plots are not. These plots yield the molecular weight from the intercepts and (μ ° − σ ° ) from the slopes. However, to obtain the individual values of μ ° and σ ° data are required for concentrations higher than those normally used for molecular weight determinations. It is further shown that once μ ° and σ ° are evaluated, they may be used to calculate satisfactorily the turbidities up to a concentration of v 2 = 0.62. Under the same circumstances the Flory‐Huggins interaction parameter χ does not reproduce the observed data as well even when χ is taken to be a linear function of v 2 .