Polymer dynamics and supermolecular structure formation during electrospinning

Orateur : Arkadii ARINSHTEIN (Department of Mechanical Engineering, Technion Israel Institute of Technology, Haifa 32000, Israel)

Electrospinning is a commonly used process for fabricating polymer-based nanofibers [1]. In this process, a semidilute polymer solution is extruded from a spinneret under strong electric field, forming a jet which undergoes extreme elongation. The theoretical modeling which was veri fied by X-ray phase-contrast imaging of electrospinning jets of poly(ethylene oxide) and poly(methyl methacrylate) semidilute solutions, predicts substantial longitudinal stretching and transversal contraction of the polymer network caused by the jet hydrodynamic forces, transforming the network to an almost fully stretched state within less than 1 mm from the jet start [2]. Further evolution of the polymer network is related to a disentanglement of polymer chains and transformation of the topological network structure. Moreover, the simple estimation of shrinking of the jet diameter caused only by solvent evaporation and by the stretching of the topological polymer network without its reorganization, shows that the final diameter of electrospun nanofibers cannot be less than 30 m, whereas their observed diameters are considerably thinner (up to two orders of magnitude). As movements of macromolecules in a topological network under high deformation rate are caused by local forces, whereas Brownian motion is negligible [3], a mechanical pulley-block system suspended by elastic springs, is utilized for the modeling of a disentanglement process. Each pulley corresponds to a topological knot ; the springs correspond to surrounded polymer chains ; the taut string connecting blocks, corresponds to a reptated chain ; and the blocks correspond to local d eformation force. It turned out that the system is sensitive to system parameters. The pulleys can approach each other, whereas the string stops. Such a behavior corresponds to formation of bundle of knots of entangled chains. In other conditions, the string continuously moves while the pulleys do not approach each other, demonstrating macromolecule disentanglement. The above analysis clarifies the disentanglement kinetics, as well as the formation of bundles of knots in rapid-deformed polymer system. References 1. A. Arinstein, and E.Zussman. Journal of Polymer Science B 49, 691 (2011). 2. I. Greenfeld, A. Arinstein, K. Fezzaa, M. H. Rafailovich, and E. Zussman. Phys. Rev. E 84, 041806 (2011). 3. A. Ya. Malkin, A. V. Semakov, V. G. Kulichikhin. Rheological Acta, 50, 485 (2011).

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