Structure and Rheology of Polyelectrolyte Complexes in the Presence of a Hydrogen-Bonded Co-Solvent.

Mor Boas,Eyal Zussman,Gleb Vasilyev,Yachin Cohen,Rita Vilensky

doi:10.3390/polym11061053

Abstract

Intermolecular interactions as well as macromolecular conformation affect the rheological and microstructural properties of polyelectrolyte complexes (PECs) solutions. The properties of semi-dilute solutions of weakly charged PECs can be controlled by the degree of ionization and solvent composition. In this work, we examined the effect of ethanol as a co-solvent on PECs composed of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) at low pH. The aqueous PECs solution was turbid, indicating formation of large aggregates, whereas PECs solution in water/ethanol (60:40 w/w) was transparent, implying no aggregation, and demonstrated higher relative viscosity than the aqueous solution, implying pronounced network formation. Imaging PECs solution by transmission electron microscopy (TEM) demonstrated aggregation, whereas the solution prepared with the mixed solvent revealed almost no phase contrast. Small-angle X-ray scattering (SAXS) of PECs in the aqueous solution indicated the presence of aggregates, while PECs in mixed solvent demonstrated a swelled macromolecular conformation with diminished aggregation. PECs with no ionic interactions in the mixed solvent assumes a homogenous network structure, which enables PECs solution processing by electrospinning.

Highlights

Processing a polyelectrolyte complexes (PECs) solution is a great challenge due to the strong complexation between the oppositely charged polyelectrolytes and solid formation or aggregation.In general, when both polyelectrolytes are fully charged, there are ionic interactions between the side-groups (PE–PE interactions) as well as hydrogen bonds with the aqueous solvent (PE–solvent interactions) [1,2]
Increased transmittance at increased ethanol concentration was measured in PECs solutions of up to 60:40 water/ethanol co-solvent
We have shown that using ethanol as a co-solvent with water for polyelectrolytes composed of

Summary

Introduction

Processing a polyelectrolyte complexes (PECs) solution is a great challenge due to the strong complexation between the oppositely charged polyelectrolytes and solid formation or aggregation. When both polyelectrolytes are fully charged, there are ionic interactions between the side-groups (PE–PE interactions) as well as hydrogen bonds with the aqueous solvent (PE–solvent interactions) [1,2]. Increasing salt concentration in a solution of oppositely charged PEs generally yields structures spanning the range from solid complexes to coacervates (elastic liquid) to dissolved polymer chains [7,8,9]. Polyelectrolyte conformation and structure upon complexation werevia studied transmittance measurements, cryo-transmission electron microscopy (TEM).

Materials and Methods

Transmittance

Rheology

Thethe

Discussion and Conclusions