Rheological Aspects and Extension‐Induced Phase Separation in Electrospinning of Poly(<i>N</i>‐isopropyl acrylamide) Solutions in Dimethylformamide

Wang, Yu; Wang, Chi

doi:10.1002/mame.201900281

Cited by 4 publications

(5 citation statements)

References 25 publications

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“…After aggregation of the chains in the concentrated domains, the inhomogeneous structure transformed into a network of fibrils, from which string-like structures are formed [ 32 , 33 ]. The emergence of the string-like structures in the straight jet of concentrated polymer solutions has been predicted experimentally [ 23 , 24 ], and this behavior correlated with our results. However, the question of the effect of entanglement remains open.…”

Section: Discussionsupporting

confidence: 90%

“…The dynamics of the polymer chains and the process of fiber formation during electrospinning remain poorly studied. Experiments revealed the appearance of a phase transition accompanied by the formation of string-like structures in the jet [ 23 , 24 ]. This behavior is consistent with the behavior of the filaments of polymer solutions under extension [ 25 ].…”

Section: Introductionmentioning

confidence: 99%

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Orientation and Aggregation of Polymer Chains in the Straight Electrospinning Jet

Субботин

Куличихин

2020

Materials

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The dynamics of a straight section of a jet arising during the electrospinning of a polymer solution without entanglements, and the orientation of polymer chains in the jet were explored based on the analysis of the forces balance equation and the rheological equation of the finitely extensible nonlinear elastic model. Two modes of the jet behavior were predicted. At relatively low volumetric flow rates, the straight jet has a limited length, after that, its rectilinear motion becomes impossible, while at higher flow rates, the jet always remains straightforward. It is shown that polymer chains in a jet can be strongly stretched, which leads to phase separation in a spinning solution. Aggregation of the stretched chains was also studied and the parameters of the emerging inhomogeneous structure were predicted.

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Section: Discussionsupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Orientation and Aggregation of Polymer Chains in the Straight Electrospinning Jet

Субботин

Куличихин

2020

Materials

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“…The highly stretched chains developed in region I may remain or survive in region II, where the extension rate becomes mild. To validate the likely flow-induced structure evolution, we have examined the PNIPAM/DMF jet after being collected in the methanol nonsolvent to confirm the presence of dissipative structures of “strings and bulges” in the flowing jet . It seems that the method of jet collection in a nonsolvent reservoir is a convenient route to freeze the internal structure of the electrospinning jet.…”

Section: Results and Discussionmentioning

confidence: 99%

“…To validate the likely flow-induced structure evolution, we have examined the PNIPAM/DMF jet after being collected in the methanol nonsolvent to confirm the presence of dissipative structures of "strings and bulges" in the flowing jet. 27 It seems that the method of jet collection in a nonsolvent reservoir is a convenient route to freeze the internal structure of the electrospinning jet. To confirm the general trend of flow-induced phase separation, more progress on other polymer solutions are provided in the following sections.…”

Section: Resultsmentioning

confidence: 99%

Formation of Dissipative Structures in the Straight Segment of Electrospinning Jets

et al. 2020

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Accurate jet diameters have been experimentally obtained during electrospinning by the light-scattering technique together with the Mie theory for cylinder scattering. Afterward, the fluid velocity and extension rate in the jet from the apex of the flow-modified Taylor cone to the straight jet end prior to the jet whipping are feasibly derived. It is found that the extension rate ε̇ is position (or time) dependent; its magnitude is the highest at the apex (region I with ε̇I) and rapidly decreases to a relatively constant value in the main jet (region II with ε̇II) before reaching the jet end (region III), where the extension rate is zero. It is of importance to notice that ε̇I could be as high as 4000 s–1, which is much higher than the chain retraction rate τe –1 obtained from the rheological measurement. This experimentally measured ε̇I is consistent with that derived theoretically based on a simple energy conservation between the electric work and the drag flow energy, i.e., ε̇I = (κ/ηe)0.5Φ0.5 E s, where κ is the solution conductivity, ηe is the elongational viscosity, E s is the electric field at the cone apex, and a parameter Φ to characterize the viscoelasticity of the flowing jet. Our analyses of the extension rate in the straight jet reveal the general trend of ε̇I > ε̇II > τe –1 > τd –1, suggesting likely a sequential structure evolution leading eventually to the strings within the jet due to, first, the flow-induced large concentration fluctuations in single phase solution (at τd –1 < ε̇ < ε̇inst. < τe –1) and, subsequently, phase separation (at ε̇inst. < ε̇ < τe –1) eventually leading to evolution of the strings with increasing ε̇ (at ε̇ > τe –1), where τd –1 is the chain disentanglement rate, and ε̇inst. is the critical stretching reate for onset of the flow-induced thermodynamically instability. To validate this hypothesis, we have developed a simple collecting method to receive the fast-flowing jet in a nonsolvent reservoir in an attempt to quickly freeze its internal structures developed, if any, for the off-line optical and electron microscopy observations. Based on the results obtained from six polymer solutions studied, the formation of dissipative structures of “strings” with various widths due to growth or ordering of phase-separated structures developed on a mesoscopic scale seems to be a general phenomenon. In situ observation of the straight jet by a high-speed camera is also performed to reveal the rapid flowing of dissipative structures of “bulges” developed by macroscopic phase separation in the jet. We conclude that the extremely high extension rate at the cone apex plays a dominant role in the subsequent structure evolution, generally producing the flow-induced phase-separated structures.

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“…This phenomenon is widely used to obtain a variety of fibrous materials that have found application in medicine, catalysis, creation of filters, and other fields [3,4]. Experiments show that the flow of a jet under the action of an electric field is characterized by a high rate of extension, which exceeds the inverse relaxation time of macromolecules, and can be accompanied by the phase transition and formation of filamentary structures in it [5][6][7]. In addition, the orientation of macromolecules along the jet axis occurs.…”

Section: Introductionmentioning

confidence: 99%

Features of the Behavior of a Polymer Solution Jet in Electrospinning

Subbotin

2021

Polym. Sci. Ser. A

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Using the numerical analysis of the force balance equation and the rheological equation of the model of finitely extensible chains, the dynamics of a charged jet during the electrospinning of a polymer solution and the orientation of macromolecules in the jet are studied. In fairly weak electric fields, the jet always remains rectilinear, while in strong fields the straight section of the jet has a finite length, after which the motion of the jet becomes unstable. This behavior is due to the competition between inertial and viscoelastic forces, with viscoelasticity dominating in strong fields. It is found that polymer chains in the jet are strongly stretched along the flow direction.

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Rheological Aspects and Extension‐Induced Phase Separation in Electrospinning of Poly(N‐isopropyl acrylamide) Solutions in Dimethylformamide

Cited by 4 publications

References 25 publications

Orientation and Aggregation of Polymer Chains in the Straight Electrospinning Jet

Orientation and Aggregation of Polymer Chains in the Straight Electrospinning Jet

Formation of Dissipative Structures in the Straight Segment of Electrospinning Jets

Features of the Behavior of a Polymer Solution Jet in Electrospinning

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