Modeling And Numerical Simulation Of Polymer Dynamic Crystallization In Flow Process

The flow has a great influence on crystal nucleation and crystal growth.In the nucleation stage,the flow will affect the nucleation shape.In the crystal growth stage,the flow affects the crystal morphology and the crystal also affects the flow.When reaching the microstructure simulation which considers the flow,we can know more about the properties of the material.In terms of microstructure simulation,the phase field model is an effective method of the material simulation,which obtains the instantaneous state of microstructure in space and time.In this paper,the phase field method was used to simulate the polymer shish-kebab crystal and the crystal morphology of the dynamic polymer crystallization in flow field.The main contents of this paper are given as follows.Firstly,the phase field model of coupled flow field is established.The existing phase field model is considered the effect of fluid flow on the crystallization,then the temperature field equation is reconstructed.According to the conservation of energy,the flow is added to the temperature control equation,and the temperature equation of the coupled flow field is obtained.A coupling coefficient is introduced in this equation so that the fluid flow rate is zero when the melt is solid.The parameters of the model are calculated through a set of experiments,and the parameters of the model can present many kinds of crystal appearance.Secondly,the phase field model is discretized.The finite difference method is used to solve the dimensionless model of dynamic polymer crystallization in flow field.Forward difference and central difference schemes are respectively used to discrete the time variable and the space variable,Laplace operator is discretized by nine-point discrete scheme.Through the FORTRAN language programming,the visual software obtains the corresponding crystallization images,and a comparison has been made.Thirdly,the phase field method is used to respectively simulate the shish-kebab of rod-like nucleus and the shish-kebab of thread-like nucleus.By changing angle of the former and the direction of axis,it can be found that the interface discontinuity can form shish-kebab formation;transverse lamellae are parallel to each other,and are distributed in equidistant distance;with the different orientation of the nucleus,shish-kebab crystal morphology is different,the dense density of transverse lamellae is not the same.However,transverse lamellae of thread-like shish-kebab crystal are irregularly distributed,and the orientation angle has little effect on the density of transverse lamellae.Finally,the effects of various factors on the crystalline morphology of the polymer(IPS)in the flow field were studied by changing the flow velocity,the anisotropy coefficient,the temperature,the dimensionless diffusion rate and the driving force parameter.Through experimental comparison,the results show that: polymer crystal is asymmetry in the flow field;the increase of anisotropic coefficient,super-cooling degree,dimensionless driving force can promote the crystal branching increased,the crystal grows thickly;diffusion coefficient is increased,which inhibited the formation of two-branches.The flow promotes the growth of the dendrite in the downstream direction and inhibits the growth of the dendrite in the counter current direction.