Phase Behavior of Polyelectrolyte Block Copolymers in Mixed Solvents

TL;DR

This study investigates how poly(n-butyl acrylate)-b-poly(acrylic acid) block copolymers behave in mixed water-THF solvents, revealing phase transitions and structures formed depending on solvent ratios using multiple advanced techniques.

Contribution

It provides new insights into the phase behavior and structure formation of polyelectrolyte block copolymers in mixed solvents, highlighting solvent partitioning effects and stabilization mechanisms.

Findings

Transition from unimers to micron-sized droplets at X=0.75

Formation of core-shell polymeric micelles below X=0.4

Droplet stabilization by hydrophilic poly(acrylic acid) moieties

Abstract

We have studied the phase behavior of the poly(n-butyl acrylate)-b-poly(acrylic acid) block copolymer in a mixture of two miscible solvents, water and tetrahydrofuran (THF). The techniques used to examine the different polymers, structures and phases formed in mixed solvents were static and dynamic light scattering, small-angle neutron scattering, nuclear magnetic resonance and fluorescence microscopy. By lowering the water/THF mixing ratio X, the sequence unimers, micron-sized droplets, polymeric micelles was observed. The transition between unimers and the micron-sized droplets occurred at X = 0.75, whereas the microstructuration into core-shell polymeric micelles was effective below X = 0.4. At intermediate mixing ratios, a coexistence between the micron-sized droplets and the polymeric micelles was observed. Combining the different aforementioned techniques, it was concluded that the droplet dispersion resulted from a solvent partitioning that was induced by the hydrophobic blocks. Comparison of poly(n-butyl acrylate) homopolymers and poly(n-butyl acrylate)-b-poly(acrylic acid) block copolymers suggested that the droplets were rich in THF and concentrated in copolymers and that they were stabilized by the hydrophilic poly(acrylic acid) moieties.