Polyelectrolyte excluded volume and expansion compared to non-ionic polymers

Abstract

Electrically charged groups attached to linear polymer chains create polyelectrolytes, which have been studied at the Weizmann Institute and worldwide for over half a century now for their basic interest and significance in biological research. Charge attachment leads to chain expansion in solution, as monitored by increased reduced specific viscosity η sp /c and radius of gyration R g , and decreasing sedimentation, s, and diffusion, D, coefficients. Macroscopic volume increase is observed in crosslinked chains following charge attachment. In the presence of added simple electrolytes electrostatic charges are screened, chain expansion is reduced, and Flory Θ dimensions and phase-separation characteristics of non-ionic polymer solutions can be achieved. A comparative discussion of an intrinsically flexible polyelectrolyte, sodium poly(styrenesulfonate) (NaPSS), and a stiff polyelectrolyte, deoxyribonucleic acid (DNA), is presented here. The early Eisenberg and Pouyet finding (J. Polym. Sci. 1954, 13, 85) that polyelectrolyte chains do not expand to full length is confirmed. The universal dimensionless function ψ = (1/4 π 3/2 )A 2 M 2 /R g 3 N AV versus a 3 (where A 2 is the second virial coefficient, M the molar mass and a the expansion coefficient) is identical for non-ionic polymers and both polyelectrolytes studied. A novel evaluation of a e , the electrostatic persistence length, is given.