Effect of Molecular Architecture on the Polyelectrolyte Structuring under Confinement

Abstract

The paper addresses the structuring and rheology of semidilute polyelectrolyte solutions with varied concentration and degree of polymer branching. The used polymer is constituted of the units of sodium 2-acrylamido-2-methylpropanesulfonate (NaPAMPS) with the branching inserts of 2-(2-bromopropionyloxy)ethyl acrylate (BPEA). The content of the branching units of BPEA in the polyelectrolytes was 6, 17, and 24%. Comparison of data obtained by small-angle X-ray scattering (SAXS) and colloidal probe atomic force microscope (CP-AFM) was used to study the effects of a solid–solid confinement on the structuring. Scattering peaks from SAXS and oscillatory force curves from CP-AFM indicate a transient network of polyelectrolyte chains with structural parameters such as interchain distance, correlation length, and interaction strength. The interchain distance and the correlation length obtained by SAXS (bulk) and CP-AFM (confinement) are in the same range, suggesting no compression of the network in the confined geometry. The interchain distance is not affected by the degree of branching at a fixed monomeric unit concentration. The correlation length (the range of ordering), the strength of the interchain interactions, and the solution viscosity, on the other hand, depend slightly on the degree of branching. The electrostatic correlation length and the interaction strength are smaller for 17% and 24% branched chains, reflecting a more disordered network.