Pearl-Necklace-Like Chain Conformation of Hydrophobic Polyelectrolyte: a SANS Study of Partially Sulfonated Polystyrene in Water

Abstract

The form factor of partially sulfonated polystyrene PSSNa (degree of sulfonation f =1, 0.72, 0.64 and 0.36), at polymer concentration 0.17M and 0.34M, without or with added salt (0 M, 0.34M, & 0.68M), is measured by Small Angle Neutron Scattering using the Zero Average Contrast method. The total scattering function is also measured, allowing extracting the distinct interchain function and an apparent structure factor. The main result is the behavior of the form factor which shows contributions of spherical entities as well as extended chain parts. This is striking for 0.64, while for f = 0.36 the sphere contribution is more dominant. The conformation does not depend on polymer concentration. When salt is added, the sphere sizes do not vary, but the contribution attributed to the stretched parts does vary very much like for fully sulfonated PSSNa. Discussion of the interchain contribution establishes that chains are interpenetrated for f= 0.64, and at the overlap limit for f=0.36. The pearl necklace model appears very suitable. Comparisons are made with analytical calculation and simulation data. While the roles of Rayleigh transition, heterogeneous architecture, and strong hydrophobicity of non sulfonated PS monomers remain to discuss, data give an accurate 3 d image of the pearl necklace.