Diffusion Characteristics Of Emulsion Impurity Clusters And Prediction Method Of Energy Storage Microsphere Defects

Hollow polymer microspheres have functions such as material isolation,controlled release,and drug delivery.Therefore,they have broad prospects in the fields of medicine,building energy conservation,food,and phase-change energy storage so on.Although hollow polymer microspheres are widely used,with the rapid development of technical means,more and more application fields have higher quality requirements for hollow polymer microspheres.For example,in the field of phase change energy storage,hollow polymer microspheres prepared by emulsion microencapsulation can be used as containers for storing phase change materials.Among them,the inertial confinement fusion（ICF）target is a representative energy storage microsphere.If the surface and internal quality of the energy storage microspheres are not good,it will cause the phase change material to permeate and lose during the phase change,and then the timeliness of the phase change energy storage cannot be guaranteed.The researchers found through experiments that when the polymer spherical shell was prepared by the emulsion micro-encapsulation method,a small amount of water was dissolved in the oil phase solution during the emulsion curing process,which caused defects such as pits at the microsphere shell at the end of curing.Because the diffusion and fusion of impurity water clusters in the oil phase will affect the surface and internal quality of spherical shell products,it is of great significance to study the growth and diffusion characteristics of water molecular clusters at the microscale in fluorobenzene solution by molecular dynamics simulation.Due to the limitations of molecular dynamics simulation in the study of large-scale clusters,a mesoscopic model of random evolution of cluster distribution based on Brownian motion is established to study the evolution process of formation,growth and diffusion of water molecular clusters in fluorobenzene solution.In addition,the mesoscopic model can also be applied to predict the location and scale of defects in phase transition microcapsules.The main research content and conclusions are as follows:（1）In this paper,the evolution process of water molecular clusters in fluorobenzene solution and the diffusion coefficient of water molecular clusters in fluorobenzene solution are studied by molecular dynamics simulation.It is found that from the perspective of the scale evolution of water molecule clusters and the number of types of water molecule clusters,with the increase of evolution time,the scale of water molecule clusters gradually increases and the number of types gradually decreases,and finally forms the only large clusters and a few free water molecules in the system.In addition,with the increase of the scale of the water molecule cluster,the corresponding diffusion coefficient gradually decreases,and the diffusion coefficient calculated by molecular dynamics simulation and the diffusion coefficient calculated by the Einstein-Stokes formula gradually tend to be consistent.At the same time,with the increase of temperature,the diffusion coefficient of water molecule clusters increases gradually.（2）In this paper,a set of stochastic evolution model of cluster distribution based on Brownian motion is constructed,which mainly studies the phenomenon of joint diffusion and fusion of double clusters,and establishes a database based on this,so as to predict the position of double clusters after fusion.It is found that the fusion probability P_RCincreases monotonically and the expectation of the distance between the centroids of the clusters increases during the limited time joint diffusion process of the double clusters,indicating that the current cluster evolution model can correctly reflect the irreversibility of the cluster system evolution.In addition,the same or different diffusion coefficient D,initial distance l,and global evolution timeΔt between double clusters have important effects on the location of clusters after fusion.（3）This paper verifies the rationality of the stochastic evolution model of cluster distribution based on Brownian motion,and further compares the data obtained by molecular dynamics simulation with the data obtained from the stochastic evolution model of cluster distribution based on Brownian motion to verify and improve the model.It is found that the stochastic evolution model of cluster distribution based on Brownian motion is suitable for studying the evolution process of impurity clusters in oil phase solution.