Bending instability

Pang JH, ClarkNA (1994) Observation of a chiral-symmetry-braking twist-bend instability in achiral freely suspended liquid-crystal films. Phys Rev Lett 73 2332-2335... 

DH. Reneker, AL. Yarin, H. Fong, S. Koombhongse. 2000. Bending instability of electrical charged liquid jets of polymer solutions in eleetrospinning. J. Appl. R/iy.y.,87.pp.4531-4547. 

Reneker et al. studied the onset of the bending instability during spinning and observed the formation of a closed single- and double-loop fiber structure called Garland. This garland structure has been observed in other copolymers like vinylidene fluoride, tetra fluoroethylene, and polyethyloazohne (Reneker et al. 2002). The fiber diameter varied from 1 pm to 1.5 pm. 

Figure 4.2 Schematic illustration of the conventional set-up for electrospinning. The insets show a drawing of the electrified Taylor cone, bending instability, and a typical SEM Image of the nonwoven mat of PET nanofibers deposited on the collector. The bending Instability Is a transversal vibration of the electrospinning jet. It is enhanced by electrostatic repulsion and suppressed by surface tension...

Keywords Bending instability of liquid jets Buckling of liquid jets Electrified liquid jets Electrospinning Elongational rheology Newtonian and rheologically complex liquids Quasi-one-dimensional equations of the dynamics of liquid jets Small and finite perturbations Viscoelastic polymeric liquids... 

In (2.1) ic = kao is the dimensionless wave number with k being the dimensional wave number and oq the unperturbed jet cross-sectional radius p and a are the density and surface tension of the jet liquid, respectively the gas density is denoted by Pg and Ii and K denote the modified Bessel functions. From several terms in the analysis of [3] describing the dynamic action of air, we keep in (2.1) only the largest one, of the order of Pg(7, since pg p. The surface tension is a stabilizing factor in the case of the bending instability, since bending results in an increase of the jet surface area [/, ( )>0, <0 for any ]. Beginning from a certain... 

The breakup length of jets in the case of the aerodynamically-driven bending instability is determined by the following expression [1,6]... 

F. 2.2 Predicted instantaneous shape of a jet with a large-scale aerodynamically-driven bending instability corresponding to the jet axis conliguratirai at t = 7 in Fig. 2.1 [1]. The cross-sectional radius ranging from 65% to 80% of its initial value (Courtesy of Pearsorr Educatirat)... 

Bending Instability of Rheologically Complex Liquid Jets... 

Fig. 2.7 Left Stereographic images of an electrically driven bending instability. The exposure time was 0.25 ms. The arrow marks a maximum lateral excursion of a loop. Right An enlarged image of the end of the straight segment of the jet. The exposure time was 0.25 ms (After [9]. Courtesy of AIP)...

A detailed theory of the bending instability of the electrified polymer jets in electrospinning was given in [9, 10] (see also the reviews [11, 23, 24] and references therein). Recasting the inequality (2.22) for the onset of the aerodynamic bending reveals that the destabilizing electric force overcomes the stabilizing effect of the surface tension if... 

Reneker, D. H. Yarin, A. L. Fong, H. Koombhongse, S. Bending instability of electrically charged liquid jets of polymer solutions in electospinning. J. Appl. Phys. 87, 4531-4547 (2000). 

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