laboratoire de physique statistique
 
 
laboratoire de physique statistique

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JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS 


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2016
Different Buckling Regimes in Direct Electrospinning: A Comparative Approach to Rope Buckling - Shariatpanahi, S. P. and Etesami, Z. and Zad, A. Iraji and Bonn, D. and Ejtehadi, R.
JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS 54451-456 (2016)

Abstract : Understanding the dynamics of direct electrospinning is the key to control fiber morphologies that are critical for the development of new electrospinning methods and novel materials. Here, we propose the theory for direct electrospinning based on theories for (liquid) ``rope coiling'' and experimentally test it. For the experiments, the buckling of microscale liquid ropes formed from polymer solutions is studied systematically using three different electrospinning setups and for different polymer concentrations. We show that different buckling regimes exist, whose dynamics are governed by an interplay of electrical, inertial, and viscous forces, and that three different buckling regimes emerge depending on the dominant forces. For low polymer concentrations, we observe an inertial regime similar to that observed for viscous liquid ropes at high velocities. By increasing the polymer concentration and consequently decreasing the rope velocity, we enter an inertial-electrical regime for which discontinuities occur in the buckling frequency as a function of applied voltage. These observations can be accounted for quantitatively by replacing the gravitational forces in viscous rope coiling theory with the electrical forces of our electrospinning experiment. Finally, for the highest polymer concentration, we observe a purely electrical regime for a solidified rope; this regime is well described by ``elastic'' rope coiling theory. (c) 2015 Wiley Periodicals, Inc.
Electrical bending instability in electrospinning visco-elastic solutions - Shariatpanahi, S. Peyman and Bonn, Daniel and Ejtehadi, Mohammad R. and Zad, Azam Iraji
JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS 541036-1042 (2016)

Abstract : The electrical bending instability in charged liquid jets is the phenomenon determining the process of electrospinning. A model of this phenomenon is lacking however, mostly due to the complicated interplay between the viscosity and elasticity of the solution. To investigate the bending instability, we performed electrospinning experiments with a solution of polyethylene oxide in water/ethanol. Using a fast camera and sensitive multimeter, we deduced an experimental dispersion relation describing the helix pitch length as a function of surface charge. To understand this relation, we developed a theoretical model for the instability for a wide range of visco-elastic materials, from conducting to nonconducting. The theoretical dispersion relation shows good agreement with the experimental results. Using the new model, we find that the elastic tension in the visco-elastic threads plays an important role in triggering the instability. (c) 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1036-1042