Molecular Dynamics Simulation Of The Mechanism Of Electric Field Force In Melt Electrospinning

Electrospinning is a manufacturing technology that uses high voltage electric fields to make polymer solutions or melts into fibers.Electrospinning has broad applications.The existing theories about electrospinning need further investigations,so it is difficult to guide the innovation and optimization of electrospinning process.For this reason,based on the all-atom model and polarizable coarse-grained model of polypropylene,molecular dynamics simulations were carried out to study the formation and action mechanism of electric field forces in melt electrospinning at the molecular level.The main research contents and conclusions are as follows:(1)The induced polarization effect and deformation behavior of polypropylene droplets in a strong electric field simulated.The influence of the electric field strength on the droplet induced dipole moment,shape,size and microstructure was also analyzed.The simulation results show that the strong electric field can induce the polarization of the melt to form an induced dipole,and the dipole moment of this induced polarization will increase linearly with the increase of the electric field strength.The application of the electric field does not significantly affect the shape of the droplet,but it can cause the droplet to expand and expand more in the direction perpendicular to the electric field.This behavior may be related to the orientation of the side chain on the polypropylene main chain induced by the electric field,which in turn causes the main chain to stretch in a direction perpendicular to the electric field.These results further illustrate that the induced polarization effect of the electric field on the melt cannot form an electric field force in the direction of the electric field that is sufficient to stretch the melt to cause significant deformation.Therefore,the induced polarization effect of the electric field on the polymer melt is not the main action mechanism of melt electrospinning.(2)The adsorption behavior of electrons,anions and cations on the surface of polypropylene droplets was simulated.The effects of charge,short-term potential interaction parameters,charged particle size,temperature and other factors on the adsorption behavior were analyzed.The mean square root fluctuation was used to estimate the amount of charged particles adsorbed on the droplet.The results show that electrons can be adsorbed on polypropylene droplets more stably,and the adsorption capacity is larger than that of anions and cations.This indicates that the polypropylene melt has a stronger attraction to electrons than anions and cations.These results also suggest that the electric field force generated by the electrons in the electric field force can be more effectively transferred to the polypropylene melt,which in turn causes the melt to move and deform.In addition,the above results further increase the possibility that the electric field force of melt electrospinning is derived from the electrons escaping from the metal surface of the showerhead.(3)In order to construct the polarizable coarse-grained model of polypropylene,a new method is proposed to determine the parameters of pairwise interaction of the coarse-grained model.The method uses the density at different temperatures as the reference,so it can ensure that the obtained parameters have good temperature transferability.In order to study the microscopic process of melt electrospinning,based on the existing coarse-grained polypropylene model,the temperature-transferable coarse-grained model of polypropylene was first constructed,and then the polarizable coarse-grained model of polypropylene was further constructed.The constructed model was verified by experimental data.The verification results show that the model has good accuracy and temperature transferability,and can describe the temperature dependence of the density and dielectric response of polypropylene.The model can be used not only to study the molecular dynamics behavior of melt electrospinning,but also to explore the rheological behavior and electro-responsive behavior of polypropylene in a strong electric field.(4)Based on the polarizable coarse-grained model of polypropylene,the diffusion and migration behavior of electrons in the polypropylene melt under the action of an electric field was investigated by molecular dynamis simulations.The results show that without the application of an electric field,the diffusion coefficient of electrons in the polypropylene melt is basically the same as that of polypropylene.After applying the electric field,the migration rate of electrons in the rectangular melt is still very slow.This indicates that the electrons in the polypropylene melt are strongly attracted and bound by the polymer chain,and it is difficult for the electrons to move relative to the polymer molecules.In nanofluids,this binding effect can be somewhat weakened.These results further illustrate that during the electrospinning process of the melt,it is difficult for the electric field to cause electrons to accumulate on the melt surface.