摘要
针对静电纺丝技术中毛细针头纺丝产量低、自由表面式静电纺丝溶液体系不稳定等问题,提出一种多叶片半封闭自由表面式静电纺丝喷头.利用MatLab软件对叶片截面曲线进行拟合,基于溶液分配均匀性建立喷头基本结构;借助Fluent流体压力仿真以及神经网络(BP)和模拟退火算法相结合的方法,计算出叶片内外层与中线的合适夹角,分别定为27°和50°;基于张力系数的计算推导出喷头内层和外层对液滴持握时间的理论公式,喷头内外层液滴持握时间分别为21.89 s和17.80 s;最后进行静电纺丝实验,验证该喷头叶片尖端可稳定形成12 股射流,纤维薄膜面积可达1 140～1 440 cm2,纤维平均直径为275 nm,变异系数(CV值)为17.49%.研究结果对于开发稳定、高效、可控的静电纺丝纳米纤维制备方法具有一定的参考意义.
Abstract
Objective In the process of electrospinning,the yield of capillary needle spinning is low and the free-surface electrospinning solution system is unstable.Therefore,it is necessary to design a new type of nozzle to ensure the stability,high efficiency and controllable preparation of electrospinning nanofibers.Aiming at the problems of multi-needle electrospinning and needle-free electrospinning,a multi-blade semi-enclosed free-surface electrospinning nozzle is proposed.Method The multi-blade semi-enclosed free-surface nozzle was primarily divided into the straight pipe section and the blade section.The straight pipe section was first designed based on the uniformity of solution distribution.Next,the blade part was modeled according to the shape and distribution characteristics of a lotus petal,with the inner and outer layers of the blade clips determined using a neural network(BP)combined with a simulated annealing algorithm.The model was then set up to verify the accuracy of the algorithm,and theoretical calculations of droplet holding time were performed for the designed model.Finally,the model's validity was confirmed through experiments.Results A multi-blade semi-enclosed free surface nozzle was designed.The straight pipe part of the nozzle adopted the method of multi-channel uniform distribution.The blade section was simulated by the lotus petal section curve.The angle between the inner and outer layers of the blade layer was calculated by combining BP and simulated annealing algorithm,and the angle between the inner and outer layers was determined to be 27°and 50°,respectively.Fluent software was adopted to simulate the final model of the above design.At this time,the pressure ratio between the inner wall and the outlet of the inner and outer layer solution in the process of electrostatic spinning was 0.45,which was close to the theoretical calculation and verified the accuracy of the theoretical model.On the basis of calculating the tension coefficient,a formula for calculating the droplet retention time of the nozzle blade was derived,and the nozzle parameters involved were included in the calculation.The results showed that the droplet holding time of the inner and outer blades was 21.89 s and 17.80 s,respectively,which is sufficient for the droplet to complete the electrospinning process and stabilize the electrospinning solution system.The identified model was 3D printed with stainless steel and electrospinning experiment was carried out.In the experiment,it was found that 12 blade tips would form a stable jet,and the efficiency was about 12 times higher than that of a single needle jet.In addition,because of the angle between the inner and outer layers in the nozzle blade,the angle between the inner and outer layers of the nozzle blades ensures that the pressure of the solution on the inner wall is the same for both layers,resulting in equal outflow speeds.The spinning area was large,and the measured fiber membrane area in this experiment was in the range of 1 140-1 440 cm2.Because the liquid supply rate was higher than the spinning rate during electrostatic spinning,the liquid droplets would not overflow on the nozzle surface or drop on the nozzle surface,and would not affect the quality of the fiber membrane.Finally,the film generated by the semi-closed free-surface nozzle with 10 mL/h supply rate and 15 min spinning time was observed by electron microscopy.The average fiber diameter was 275 nm and the CV value was 17.49%.Conclusion Combining the advantages of single-needle and free-surface nozzle in electrospinning,a semi-enclosed free-surface nozzle with multiple blades is proposed and designed.It has the advantages of multi-jet formation,long droplet holding time and no solution volatization.Compared with conventional single needle electrospinning,the efficiency is improved and the spinning area is enlarged.Compared with electrospinning without needles,the solution utilization rate and stability of electrospinning solution are improved.Through the electrospinning experiment and the electron microscopy of the fiber membrane,the average diameter of the fiber film produced by the nozzle is 275 nm,with a diameter coefficient of variation(CV)of 17.49%,indicating excellent fiber characteristics,and this study has certain reference significance for the development of stable,efficient and controllable electrospinning nanofibers preparation method.
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