Effect of Self-Assembly on Probe Diffusion in Solutions and Networks of pH-Sensitive Triblock Copolymers

Abstract

Self-assembly of amphiphilic BAB triblock copolyelectrolytes into a transient network was induced by decreasing the pH, which decreases the ionization degree (α) of the polymers. The exchange time of the lateral hydrophobic blocks (B) between micellar cores, and therefore the lifetime of the cross-links, was varied by varying α. Probe diffusion (D) in the medium was determined for dextran chains with two different radii and for latex spheres using fluorescence recovery after photobleaching and dynamic light scattering, respectively. The effect of self-assembly was determined by measuring D in situ while α decreased. The dependence of probe diffusion on the copolymer concentration was determined at steady state for different values of α. Diffusion of the latex particles, which were much larger than the pore size of the network, was determined by the lifetime of the cross-links. Diffusion of the dextran chains slowed down when the copolymers self-assembled into a network, but it was insensitive to the lifet...