(161bb) Dynamically varying coupling between operating parameters determines regime-specific cone/jet features in polymer electrospinning

Despite numerous studies investigating both fundamental and applied aspects of polymer electrospinning, critical knowledge gaps in system characteristics and process dynamics often hinder precise control over fiber properties and effective use of electrospun meshes. In this study, we conducted imaging experiments and electrohydrodynamic simulations to examine the effects of voltage (V)- throw distance (T) coupling in influencing the onset of electrospinning regimes and the dynamics of regime-specific cone/jet features. Using a solution of polycaprolactone – a synthetic, biodegradable polymer widely used in several applications – we first identified four distinct regimes, viz. dripping, cone-jet, rotational and multi-jet as systematic functions of varying V and T. Once initiated, the rotational regime, characterized by a non-axisymmetric instability, was sustained for constant values of V and T. This regime also served as a transition between the stable cone-jet and the stochastic multi-jet regime. Contrary to previous reports, the cone-jet regime could be sustained over a large potential drop (V/T) range through a judicious choice of operating parameters. While small changes to the collector position affected the electrospinning jet at the needle tip and effected regime transitions despite the large scale separation, V was the primary factor determining the onset of electrospinning regimes at very large T. Thus, the nature of V-T coupling and the relative dominance of the coupled parameters varied dynamically as a function of specific operating conditions. V-T maps generated from these experiments provided operating windows to promote desirable regimes and potentially, specific fiber properties. Next, we investigated and characterized quantifiable and universally identifiable cone/jet features within specific regimes across independently varied V and T experiments. In the cone-jet regime, as the potential drop was increased, the cone angle and jet length increased while the initial jet diameter displayed bi-phasic behaviour. Likewise, in the multi-jet regime, the maximum number of splits increased with increasing potential drop. Although these trends were qualitatively consistent across varying V and T experiments, power-law based correlations extracted from plots of cone/jet features versus theoretical potential drop indicated stronger influence of V than T. Using mechanistic insights from electrohydrodynamic simulations, we showed that both V and T exerted their influence through changes in charge density, electric field strength and distribution of electric field lines in the cone’s vicinity. In summary, our results significantly contribute to the current knowledge on regime onset/transitions and the effect of theoretical potential drop on regime-specific cone/jet features in polymer electrospinning. A deeper understanding of these aspects can provide a handle to ultimately modulate fiber properties real-time and lead to the development of electrospun meshes with specific properties.

Keywords: Polymers & Composites, Polymer Processing, Electrospinning