Papers by Author: Gao Feng Zheng

Abstract: In order to control the machining process of Direct-Write based on Near-field Electrospinning automatically, an automatic programming system used for an open architecture CNC system is proposed in this paper. This system descirbes the machining trajectory via the 2D CAD drawing, from which the data is extracted by the system. According to the processing parameters, the data is classified and reordered, and NC codes are automatically generated. The system solves the problem in integrating the design and machining, makes it more convenient to experimental research and realizes patterned fabrication of micro/nano-structure,which provides a good experimental base for the development of electrospinning technology.

Abstract: Near-Field Electrospinning (NFES) is a newly developed method to fabricate continuous and ordered solid nanofibers, with smaller spinneret-to-collector-distance the behavior of viscous jet would play a more prominent effect on the deposition and morphology of nanofiber. In this paper, a 2-dimentional physical model based on electrohydrodynamics and rheology was set up to discuss the morphology of viscous jet for NFES. The profile of the jet along z direction can be predicted by this model, and the impact of process parameters on the jet radius is analyzed. Radius of jet decreases with spinneret-to-substrate-distance decreasing; jet radius decreases with applied voltage and electric field strength increasing; jet electrospun from PEO solution is thinner than that from PVA solution with the same solution concentration; solution concentration has insignificant influence on the radius of jet from solution of the same polymer (PVA or PEO). This numerical simulation would improve the control of electrospinning process in NFES.

Abstract: NFES is a new and simple way to realize precision-positioning of nanofiber. A model on NFES nanofiber movement is built to analyze the effects of the existed nanofibers which have been collected on the substrate, on the nanofiber’s dropping movement. During electrospinning nanofiber is affected by the electric field force, Coulomb repulsive force, air resistance force gravity and so on. The influence of parameters on the deposition behavior of as-spun nanofiber is discussed. The simulation results show that (i) with charge density increasing, the final spacing between mass center of nanofibers A and B (FSAB) increases and the movement distance of center-of-mass of nanofiber B (MDB) decreases first and then increases; (ii) FSAB increases with applied voltage, but decreased in narrow range with concentration of PEO increasing; (iii) FSAB decreased with the initial spacing between mass center of nanofibers A and B (ISAB) increasing, and then it increases after reaching the minimum. So does ISAB to DMB. This simulation model would improve the controlling of nanofiber in NFES.

Abstract: Direct-Write (DW) technology based on Near-Field Electrospinning (NFES) was introduced to fabricate suspended micro/nano-structure on pattern substrate, and the deposition behaviors of DWed structure under different collector motion speed (CMS) were discussed to improve control of DW technology based on NFES. Deposit point of DWed structure on the substrate can be controlled accurately under the observation of microscope, and position error of micro/nano-structure is less than 5µm. When CMS is compatible with the electrospinning speed, straight line micro/nano-structure can be direct-written across micro-trenches with width of 5~40µm or to bridge two micro-pillars with diameter of 10µm. Due to the water evaporation and surface tension force, DWed structures suspended in the air would shrink smaller compared with that deposited on the top surface of pattern. The shrink ratio of micro-structure is higher than nano-structure and the shrink ratio decreases with the solution concentration increases. When the CMS is lower than electrospinning speed, the electrostatic force and elastic force would play a more prominent role on the deposition behavior of DWed structure. The electrical field strength on the top surface of pattern is higher than the space between two patterns, DWed thin film would deposit along the trip pattern and nanofiber would prefer to aggregate on the top surface of pattern under electrostatic force. When solution concentration is lower than 18%, nanofiber aggregate on the pattern would coagulate to form polymer bundle.