Surfactant-Mediated Transitions in Cone/Jet Dynamics and Fiber Morphology during Aqueous Electrospinning

Aqueous electrospinning suffers from inherent processing challenges and often results in intermittent jetting, bead formation, and poor fiber continuity. Although surfactants can mitigate these limitations, the relationships between surfactant-mediated cone/jet dynamics and resulting fiber morphologies remain poorly understood. Previous studies involving surfactants have primarily focused on fiber properties while paying limited attention to the cone/jet region where the force balance governing fiber formation is established. In this work, we holistically investigate solution properties and in situ cone/jet features to elucidate the combined effects of the nonionic surfactant Tween 20 and relative humidity on aqueous electrospinning of poly(ethylene oxide). Surfactant addition reduces surface tension and increases conductivity without affecting bulk viscosity, thereby promoting stable jetting, reducing jet length, and advancing the onset of the bending instability. Notably, transitions from convex-concave to unpinned concave cone shapes occur without alterations to other operating parameters, indicating a shift in the electrocapillary balance. Surfactant addition promotes earlier cone-region thinning, suppresses bead formation, and increases fiber diameter, with higher surfactant concentrations inducing fiber fusion. Independently, increasing the relative humidity alters jet length and induces systematic transitions among broken fibers, beads-on-a-string, and bead-free morphologies. Importantly, the concentration window over which bead formation and fiber breakage occur shifts to higher surfactant concentrations at higher humidity. Together, these observations indicate that surfactant-mediated changes in cone/jet dynamics alone do not fully explain the resulting fiber morphology during aqueous electrospinning and suggest an additional contribution from evaporation-limited drying. Our work provides mechanistic insights into the coupled roles of surfactant-mediated effects and humidity-dependent jet solidification in determining fiber morphology during aqueous electrospinning.