From Polyelectrolyte Complex Solution to Electrospun Fibers

Mixing semi-dilute solutions of highly charged oppositely polyelectrolytes (PEs) generally yields compositions spanning complexes (solid) to coacervates (elastic liquid) to dissolved solutions with increasing salt concentration. In case one of the PEs is weakly charged, the PE pair can be dissolved without salt by adding an organic co-solvent. Such a system was recently studied with 1:1 (by monomer ratio) poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) dissolved in a mixture of water/ethanol. Rheological investigation of semi-dilute solution demonstrated maximal relative viscosity at 40% ethanol. The PECs in aqueous medium was opaque but at 40% ethanol solution was transparent. Extensive stretching and confining this solution by electrospinning results in 300-600 nm fibers. Polarized FTIR demonstrates preferred macromolecular orientation along the fiber axis which implies a better packing of macromolecules due to their orientation along the fibers. The fibers demonstrate pH-responsive behavior with 17% ionization degree and an increase in fiber diameter of 600% in a gel-like structure at low pH. At neutral pH, the ionization degree is at least 79% and deswelling is observed, demonstrating high fiber stiffness (increased by 10⁴) with minimal water consumption.