Population Balance-monte Carlo Simulation For Self-assembly Of Core-shell Structure Oxygen Carrier In Aqueous Suspensions

In a wide range of engineering application,the material active design has arouse attention of researchers.According to the need of engineering application,high performance materials are prepared based on deep understanding of the chemical and physical properties of raw materials.As an active design method,self-assembly method can produce a high-performance core-shell structure material to be the oxygen carrier in the process of chemical looping combustion.This method adopts two different types of oppositely charged and large scalar differences particles in aqueous solution,such as micro-Al₂O₃??m-Al₂O₃?and nano-TiO₂?nm-TiO₂?,to form the core?micro-Al₂O₃?-shell?nano-TiO₂?structure by self-assembly interaction.This kind of core-shell structure material has good reactivity,but under the different preparation conditions,such as pH,salt solution concentration,initial particle size,etc.,the final product properties are quite different.So in view of the nano TiO₂-micro Al₂O₃self-assembly process,this article studies the influence of various factors depending on theoretical analysis and numerical simulation,in order to guide the tailor-making of core-shell microarchitecture of particles suspended in aqueous suspensions.The nature of the self-assembly process is the agglomeration of two component particles,including homo-aggregation and hetero-aggregation.This process involves the Brownian motion of the particles in the solution,as well as the van der Waals forces,electric double layer repulsive/attractive potentials and hydration.Therefore the theoretical model adopts the Brownian motion model in continuous regime and the extended Derjaguin-Landau-Verwey-Overbeek?DLVO?theory.A charge-balance model is developed to view the change of particle surface electrostatic potential issued from the aggregation of primary particles with different surface potentials,and the particle aggregate structure is described by the fractal theory.The theoretical analysis shows that electrostatic force is the main self-assembly control force,and the hetero-aggregation leads to the change of surface potential,which makes a significantly change of the electrostatic interaction between particles.A fast differentially weighting Population balance-Monte Carlo?PBMC?simulations is utilized to simulate the self-assembly process.This numerical simulation method can effectively improve the computation efficiency,ensure the accuracy of computation and avoid the huge computation cost in two component aggregation.To validate the PBMC simulation,a dynamic light scattering experiment is conducted and the aggregation process between different kinds of particles is analysed.The simulation algorithm quantifies the effect of various forces in the solution by calculating the attachment efficiency,i.e.the probability of the aggregate formation after the collision between particles.The initial stage of hetero-aggregation maintains attractive with a high attachment efficiency.After a certain coated number of TiO₂ particles,the attractive force drops rapidly and the hetero-aggregation weakens.Simulation can also reveal the dynamic evolution of the aggregation.Al₂O₃-TiO₂ hetero-aggregation and TiO₂homo-aggregation will occur firstly,then Al₂O₃ homo-aggregation will happen after a certain degree of hetero-aggregation.According to the specific application,the effects of pH and ionic strength?IS?on attachment efficiency and coverage effect of the final core-shell composite particles are studied.IS has a more noticeable impact than pH,and the optimation conditions of IS and pH is found.This findings look promising for understanding inherent particle dynamics and rationalizing self-assembly process of core-shell microarchitectures.