Polymeric Micro/nanofibers Deposited Using Near-field Electrospinning And Their Applications

One-dimensional nanostructures, which have large specific surface area and special optical, electrical and magnetic properties, have been the hotspot of material research in the today's world. Among them, the polymeric nanofibers have attracted tremendous research interests due to their good flexibility. Electrospinning is a common method to produce nanofibers of different kinds of materials ranging from a few micrometers down to a few nanometers. However, the nanofibers fabricated by conventional electrospinning are random, which has limited their application. Therefore, an orderly electrospinning technique, Near-field electrospinning (NFES), has been developed, and used to fabricate various polymeric micro/nanofiber patterns. Based on electrospun polymeric fibers, several micro/nanodevices have been created, such as Poly (vinylidene fluoride) (PVDF) piezoelectric actuator, polyaniline (PANI) electrostatic actuator and micro/nanofluidic channels. The main research contents were as follows.1. An orderly electrospinning technique, NFES, has been developed to deposit polymeric micro/nanofibers in a direct, continuous, and controllable manner. In NFES, the distance between spinneret and collector is decreased to a few millimeters to achieve stable polymer jet, thus enabling orderly deposition of micro/nanofibers. Using a programmable X-Y stage to control the trajectory and moving speed of the collector, we fabricated various poly (ethylene oxide) (PEO), PVDF and PANI micro/nanofiber patterns. Scanning Electron Microscope (SEM) has been used to investigate the morphology of fabricated micro/nanofibers, and the influence of electrospinning parameters on fiber diameter has been discussed. This technique makes electrospinning a potential tool in direct-write micro/nanofabrication for possible applications in micro/nanodevices, such as generator, sensor, actuator and micro/nanofluidic devices.2. The application of electrospun polymeric micro/nanofibers in actuators. (1) Piezoelectric actuation of doubly clamped, suspended PVDF fibers fabricated by a direct-write process has been demonstrated. NFES technique was utilized to fabricate PVDF fibers with good piezoelectric properties by means of the in situ electrical poling process. Experimentally, PVDF fibers have responded to both piezoelectric and electrostatic effects in applied electric field, and double-layer electrodes have been used to minimize the contribution of electrostatic effect to the measured results. The electrospun PVDF fibers have an average piezoelectric coefficient d33 of -57.6pm/V, which is nearly twice of the value reported in PVDF thin films. (2) The electrostatic actuator with cantilever structure was fabricated based on electrospun PANI nanofiber, and the displacement of PANI cantilever beam under electrostatic force was measured. When the voltage of 270V was applied, the free end of PANI cantilever beam had a displacement of 1.2μm.3. The application of electrospun polymeric micro/nanofiber in micro/nanofluidic channel fabrication. PVDF and PEO micro/nanofibers were patterned on a Si substrate using NFES technique to serve as a template to form micro/nanochannels in PDMS. Due to high control of our NFES process, diverse patterns could be realized corresponding to desired applications. Based on NFES technique, we created various micro/nanochannel patterns, such as parallel channel array, cross-linked microchannels,'Cal','A'and'O'channel patterns. The cross section of fabricated channels was investigated under SEM and the accessibility of channels was tested under fluorescence microscope.