Light Scattering of Electrospinning Jet with Internal Structures by Flow‐Induced Phase Separation

Abstract

Herein, the direct morphological evidence of the extension‐induced phase‐separated structures in the electrospinning jet observed by high‐speed video imaging and by light scattering technique is reported. Model solutions of poly(vinyl alcohol) (PVA)/water are electrospun. Two types of internal structures, that is, long strings and short ellipsoids, are found. A light scattering model is derived for the Vv scattering configuration to account for the scattered intensities contributed from the liquid jet itself and those from the internal structures. For the severely stretching jet of PVA/water, the Vv intensity profile is dominant by the internal structures to mask the scattering contribution from the jet itself. Moreover, the Hv intensity profile reflects the anisotropy of the oriented chains parallel to the jet axis. For the 7 wt% solution, the derived extension rate in the vicinity of the Taylor cone apex is about 3420 s−1, which is higher than the Rouse relaxation rate measured by rheometer. It is concluded that extension‐induced phase separation of the single‐phase PVA solution is likely to occur in Taylor‐cone apex to trigger the self‐assembly process for producing strings (and/or bulges) in the flowing jet, which eventually transform to become the nanofibers, after solvent removal, to be collected on the grounded collector.

Preparation and Characterization of Electrospun PAN-CuCl2 Composite Nanofiber Membranes with a Special Net Structure for High-Performance Air Filters

“…The instability of the Taylor cone caused by the high electrostatic field leads to the formation of the electrospray droplets. The increased solution conductivity, leading to increased instabilities of the charged droplets, finally gave rise to the formation of the net structure during the electrospun process [ 28 , 29 ]. The occurrence of rapid phase separation on the splitting membrane may lead to the formation of a net structure within milliseconds.…”

The Elasticity of Polymer Melts and Solutions in Shear and Extension Flows

“…However, only low Weissenberg numbers were considered. Experiments show that the extension rate in the cone/jet transition region exceeds the inverse chain relaxation time ( ) which results in unfolding of the polymer chains, such that they are stretched inside the jet [ 155 , 163 , 164 ].…”

Integrating a micro-mixing mechanism and on-line thermal processing for the large-scale ejection of polymeric liquid threads for producing ultrafine fibers

“…The term micro-mixing refers to an intricate intermixing phenomenon occurring at small length scales, typically within the micrometer range, resulting in the mixing of both fluid phases. The approach is based on a pneumatic ejection of polymer solutions at high liquid flow rates, 23–25 of the order of tens of milliliters per hour, much higher than those used by standard techniques (≪1 mL h −1 ), 26,27 followed by thermal treatment with a tubular furnace, in a single-step. Our method uses a so-called Flow Blurring (FB) atomizer 23,25,28–30, to fragment a liquid stream with a gas current, thus generating multiple, thin liquid threads that elongate as they move forward 25,31,32 and are dried in-flight producing micro/nanofiber mats.…”