The electrostatic free energy of polyelectrolyte solutions. II. Fully stretched macromolecules

Abstract

Abstract ( 1 ) The electrostatic internal energy of a solution of rodlike, ionized polymolecules is calculated by an integration which makes use of the molecular potentials evaluated previously. ( 2 ) The electrostatic free energy is calculated by a charging process for which the reference state is a discharged solution of the same concentration as that of the charged solution. ( 3 ) A series of graphs is presented for the numerical evaluation of the internal and free energies of salt‐free polyelectrolyte solutions as a function of concentration, degree of ionization, and temperature. ( 4 ) The osmotic pressure of stretched polyelectrolytes is calculated from the free energy expression. The calculated osmotic coefficients are practically independent of molecular weight and polyelectrolyte concentration, and are determined by the degree of ionization. A comparison with the measurements of Kern on salt‐free polyacrylic acid at higher degrees of ionization (for which the macromolecules are stretched) gives a very satisfactory agreement. ( 5 ) An expression for the light scattering by polyelectrolyte solutions is derived from the equation for osmotic pressure and discussed briefly.