Controlled deposition and alignment of electrospun PMMA-g-PDMS nanofibers by novel electrospinning setups

Abstract: Electrospinning is a useful technique that can generate micro- and nano-meter sized fibers from polymer materials. Modification of the electrospinning parameters and apparatus can generate nanofibers for use in diverse applications ranging from tissue engineering to nanocomposite fabrication; however, electrospun fibers are typically collected in a random orientation and over large areas limiting their applications.  Here we present several methods to control the deposition of electrospun nanofibers, such as the use of a single auxiliary electrode ring and a negatively charged collector substrate to control the deposition area and the construction of a parallel electrode collector known as the triple electrode setup to control the uniaxial alignment of nanofibers. The numerous constructed setups were advanced by the use of electric field computations to assess the distribution of the electric field and its effect on the deposition behavior and morphology of the electrospun nanofibers. The electrostatic force imposed by the auxiliary electrodes provides converged electric fields that direct the nanofibers to their desired deposition targets. Here it is shown that the use of the auxiliary electrode ring dramatically decreased the deposition area of nanofibers, the negatively charged substrate yielded more uniform nanofibers and the triple electrode setup is a viable method to achieve uniaxially aligned nanofiber mats.    The electrospinning of copolymers appears as an attractive option for enhancing the overall properties of nanofibers as it offers possibility of an intrinsic control of the polymeric material itself. The poly(methyl methacrylate)-graft-poly(dimethylsiloxane) graft copolymer  (PMMA-g-PDMS) is considered to be an organic-inorganic hybrid material with much potential in its use in nanocomposites, and in this work has been successfully synthesized and electrospun via the various constructed electrospinning setups.   In the final elements of this work, the triple electrode setup is used in combination with a dynamic rotating collector to yield a novel collector and has been successfully used to produce PMMA-g-PDMS nanofiber sheets that were further incorporated in a PDMS matrix to yield nanocomposite sheets. A variant of the triple electrode setup with partially insulated electrodes is devised in combination with a methodology to remove the nanofibers from the collector. The nanofibers once removed and dried were incorporated in a PDMS matrix to yield nanocomposites. The preferential dissolution of the fibers from the matrix rendered the fibers to templates and a final porous material with uniaxial nanochannels could be obtained.   This work is believed to be able to lead to a better understanding of the mechanisms of nanofiber deposition and alignment, and should be of help to the design of more practical collecting structures, hence promoting the applications of the electrospinning technique.