| Electrospinning is a easy and efficient way to fabricate nanofiber. The charged jetaccelerated by electric field force and then travels straight toward the collector for somedistance before a bending instability develops into a series of expanding loops. During theprocess, the solvent evaporates as the jet moves which decreases jet radius and increases thepolymer concentration and viscosity. When the solvent fully evaporates, jet stretching stopsand resulting solid fiber of greatly reduced diameter deposits onto the collector. The path ofjet and diameter of fiber is affected by various parameters. People applied magnetic field tomake a control to the chaged jet and there are many excellent work. Magnetic-field-assistant-electrospinning (MEAFS) can get alignment fiber by introducing a pair of permanent magnetsparallel to each other as the collector.It is necessary to get a theory understand of the bendinginstability motion of jet and mechanism of MEAFS. This paper focus on the model of electricfield distribution and jet motin in tip-plane device as well as magnetic field distribution andit’s effect on jet motion in MEAFS.Finite element software ANSYS is employed to analyze the electrostatic fielddistribution from the capillary nozzle to the grounded plane (tip-plane system) in theelectrospinning system. As a result, the electric field show an exceeding uneven distributionand high strength near the nozzle but relative even distribution and low strength near thecollector. Smaller collector diameter or shorter distance between nozzle and collector can leadto higher electric field strength both near nozzle and collector, but only when the size ofcollector and the distance of nozzle to collector is roughly equal, the electric field distributioncan be even. The model established by Reneker and Yarin was refered to simulate the path of chargedjet as it moves toward the grounded collector, which take the jet as a string of beads connectedby Maxwell element with consideration of solvent’s evaporation and jet’s solidation. Theprogram utilizes the Runge-Kutta-Merson method for numerical integration to solve thesystem of equations. We simulated the jet path for tip-pane（nonnuiform electric field） andplane-plane(uniform electric field) electrospinning device. Further more, wo studied how thejet affectted by different electrospinning parameters including voltage, distance between tipand collector and the concentration of solution. The results show that, increasing of voltage,decreasing of distance from tip to collector and increasing concention of solution can led toincreasing of fiber’s diameter.The magnetic field distribution of permanent magnets used in MFEAS was simulatedwith ANSYS, the results show an exceeding uneven distribution and high strength nearmagnet. Magnetic flux density is maximized up the parallel permanent magnet and dominatedby horizontal component and decrease quicely as far away form it. The vertical component ofmagnetic flux density is dominated near the margin of the permanent magnet. Increasing thedistance between the two magnets, magnetic flux density decrease in the middle of the twomagnetic and the vertical component of magnetic flux density increased in the inside of theedge.We get the analytical expression of two permanent magnets and intrduce it in themomentum equation to study the effect on jet motion. The result shows that the magnetic fieldcan accelerate the down velocity of jet up to the permanent magnets which is benefit for thealliginment of fibers. The aliginment of fibers is result from electric field and manetic fieldcaused by the two parallel placed magnet. |
PDF Full Text Request