Low-Voltage AC Field Waveforms in Electrospinning: Waveform-Dependent Control of PVP Nanofiber Diameter and Mat Uniformity

Résumé fourni par la source

A low-voltage alternating current (AC) field (20 V peak-to-peak, 1 kHz) was superimposed on a conventional direct current (DC) electrospinning configuration in order to test whether the shape of that perturbation measurably alters fiber formation. A function generator delivered sinusoidal, pulsed (square), ramp and arbitrary (noise) waveforms to a foil-covered flat collector, while a standard DC high-voltage source (20 kV) drove the jet from the spinneret. Polyvinylpyrrolidone (PVP) nanofibers were characterized by scanning electron microscopy (SEM), fiber-diameter distribution analysis (FIJI/ImageJ), quantitative orientation analysis and contact profilometry. One-way analysis of variance across the six conditions was significant (F(5.594) = 5.56, p = 5.1 × 10−5) but the associated effect size was small (η2 = 0.045). Relative to the connected control (237 ± 52 nm), the ramp (205.5 ± 43.9 nm), noise (201.3 ± 48.6 nm) and pulse (212.6 ± 70.0 nm) waveforms yielded significantly finer fibers (Tukey HSD, p = 0.0008, 0.0001 and 0.022, respectively); relative to the grounded control (215 ± 47 nm), no waveform reached significance. The ramp waveform produced the narrowest diameter distribution but, unexpectedly, the roughest mat of the four AC conditions (Ra = 1.95 µm against 0.74 µm for the grounded control), while the noise waveform gave both the smallest mean diameter and the smoothest mat (Ra = 0.61 µm); with a single profile per scan direction, these roughness values are descriptive rather than statistically compared. Quantitative orientation analysis using two independent estimators (structure tensor and fast Fourier transform) returned Herman orientation factors of S ≤ 0.13 for every condition, against S = 0.81 for a partially aligned reference population: no condition exceeded the isotropic noise floor of the FFT estimator (S95 = 0.141), and the three conditions that marginally exceeded the structure-tensor floor (S95 = 0.104) included the connected control, which received no oscillating signal. No waveform, including the pulsed waveform, produced fiber alignment attributable to the AC field. The applied AC amplitude corresponds to approximately 0.05% of the DC voltage, and the associated oscillating field (±50 V m−1) is approximately three orders of magnitude smaller than the mean DC field (~1 × 105 V m−1); the electrohydrodynamic mechanisms discussed here are therefore presented as hypotheses requiring direct measurement rather than as established explanations. Within these limits, low-voltage waveform modulation is a simple, safe and retrofittable route to modest control of nanofiber diameter and mat uniformity in a single-polymer system, but it does not induce fiber alignment.

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