Charge transport in electrospinning of polyelectrolyte solutions

Abstract

This study elucidates the electrical charge transport during electrospinning of weak polyelectrolyte (poly(acrylic acid) (PAA)) solutions by employing current emission measurements. With pH variation, the PAA ionization degree could be controlled from uncharged at low pH to weakly charged at intermediate solution pH. Electrospinning neutral poly(vinylpyrrolidone) (PVP) as a reference polymer solution confirmed established current–flow rate scaling relationships as shown by De La Mora & Loscertales (1994), I~(γKQ)^ν, independent of the applied electric field polarity, where ν = 0.5, K is the conductivity, γ is the surface tension, Q is the flow rate, and I is the current. Similarly, the uncharged PAA did not display any polarity dependence, yet ν ≈ 0.8. Negatively charged PAA, however, showed a marked deviation in the current–flow rate behavior, which was affected by the applied electric field polarity. In the case of negative polarity, ν = 0.99, whereas for a positive polarity ν = 0.68. Similarly, the voltage required for stable cone jet electrospinning of charged PAA was significantly higher in the negative polarity configuration for all tested flow rates (300-1600 µL/h). As opposed to merely surface charges typically considered when electrospinning leaky dielectric fluids, as suggested by Melcher & Taylor (1969), our results suggest that the measured current is also affected by volumetric charges from charged PAA in the bulk of the jet. The proposed additional charge transport might affect the orientational order within PE based nanofibers and their diameter.