Effect of isopropanol cosolvent on the rheology and spinnability of aqueous polyacrylic acid solutions

We investigate the effect of alcohol fraction (isopropanol, IPA) in a binary water-alcohol solvent mixture on the shear and extensional rheological properties, as well as the role of viscoelasticity on fiber formation of poly(acrylic acid) (PAA) in electrospinning. Comparison of the scaling of both specific viscosities η_sp and extensional relaxation times λ_E of PAA in water–IPA mixtures, showed stronger scaling compared to salt-free aqueous polyelectrolyte solutions, except for the η_sp in the unentangled regime displaying a polyelectrolyte-like scaling η_sp ~ c^0.5 for all IPA%. Such deviation suggested IPA induces association/aggregation of PAA. However, the trends between η_sp and λ_E magnitudes as a function of IPA% differ for concentrations compared in the entangled regime. The η_sp as well as their elastic moduli exhibit a maximum, whereas λ_E increases monotonically with IPA%, suggesting a complex interplay of various interactions are dictating their structure in water-IPA mixtures, affecting their shear and extensional response differently. Electrospinning experiments showed increasing IPA% reduces the onset of both beaded and uniform fibers. Analysis using dimensionless numbers indicated the enhancement of their elasticity by IPA, and the consequent stabilizing effect on their jets/filaments against break-up during electrospinning, plays a role in the improvement of their fiber formation.