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Controlled Encapsulation of Hydrophobic Liquids in Hydrophilic Polymer Nanofibers by Co-electrospinning


  • We thank Mr. A. Gómez, from E. S. Ingenieros de Sevilla, Spain, for measuring the surface tension of the different liquids, and Ms. E. Rojo from University of Basque Country, Spain, for kindly helping us with the rheological characterization of the melts. Finally, we acknowledge Prof. Juan Fernández de la Mora for helping us to improve the experimental setup. We acknowledge the support of the Spanish Ministry of Science and Technology under projects DPI2004-05246-C04 and NAN2004-09312-C03, and of Yflow SL.


There are many technical situations, such as various biological or medical applications, in which a hydrophobic fluid must be encapsulated inside a hydrophilic polymer shell in the form of tiny microscopic pieces. A novel approach is presented, based on the co-electrospinning of the hydrophilic polymer melt (outside) and the hydrophobic fluid (inside), which results in beaded micro- and nanofibers, such that the hydrophobic fluid is efficiently encapsulated inside the beads. For the selected fluid couple, the low liquid–liquid surface tension and the high viscosity of the melt prevent the varicose break-up of inner fluid in the coaxial electrified jet until the very end of the co-electrospinning process. The resulting fibers present beads filled with the hydrophobic fluid, separated by a rather uniform distance whose length depends partially on the melt flow rate. The bead diameter grows with the inner flow rate, going from a monosized to a bisized distribution. In the case under study, the maximum relative (inner-to-outer) flow rate is one. The diameter of the solid fibers between beads scales well with existing theories for simple electrospinning.

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