Structuring of Polyelectrolyte (NaPSS) Solutions in Bulk and under Confinement as a Function of Concentration and Molecular Weight

Abstract

The present paper gives a deeper insight into the chain ordering in aqueous polyelectrolyte solutions under geometrical confinement as a function of degree of polymerization and polymer concentration. Colloidal probe atomic force microscopy (CP-AFM) and small-angle X-ray scattering (SAXS) are used to compare the poly(styrenesulfonate) (NaPSS) chain ordering between two solid interfaces and in bulk, respectively. Oscillatory force–distance curves from CP-AFM as well as the scattering peaks from SAXS indicate a near range ordering of polyelectrolyte chains with structural parameters such as interchain distance, correlation length, and the strength of ordering. These characteristic lengths from CP-AFM (confinement) and SAXS (bulk) are in the same range. The interchain distance is up to 20% smaller and the correlation length is up to 20% higher under confinement, indicating a slight compression of the polyelectrolyte chains and a stronger counterion condensation under confinement. The interchain distance d sc...