Mesoscale Brownian Dynamics Simulation On Self Assembly Behaviors And Model Of CTAC/NaSal Surfactant Rodlike Micelless

Surfactant molecules in solution can self-assemble into a variety of micellar structures,and one of which is called the rodlike micelle.In static solution,the free surfactant molecules continuously exchange with the ones forming rodlike micelles to maintain a dynamic equilibrium.But when the solution condition(such as the concentration,temperature and shear rate)changes,the self-assembly state of surfactant molecules will change accordingly to adapt the solution change.Consequently,the rodlike micelle grows or shortens,affecting the three dimensional space structure of micelles,and afterwards changing the macroscopic properties of the solution.Surfactant rodlike micelles are widely used in various fields of the national economy due to the unique self-assembly behaviors and the resulting rheological properties.However,there is no self-assembly model at present to describe the coupling relations between self-assembling behaviors of rodlike micelles and solution conditions.Therefore,the self-assembly state of rodlike micelles with solution condition can not be predicted in industrial production,which limits their practical application.There are two difficulties to establish the self-assembly model.One is that the self-assembly behaviors of rodlike micelles change dynamical and are quite complex with solution conditions.The other is the cross-scale between microscopic self-assembly behaviors and macroscopic solution conditions,leading to great difficulty to couple them.Based on the above,the present study utilizes the length of rodlike micelle to correlate their self-assembly behaviors and solution conditions,and meanwhile to represent the self-assembly degree of themselves.Mesoscale Brownian dynamics simulation will be carried out to study the self-assembly behaviors of rodlike micelles,aiming to obtain the quantitative relationship of the undetermined parameters in the established differential equation and time under different solution conditions.Afterwards the established differential equation can be integrated,and consequently the self-assembly model of rodlike micelles will be established to further explore their self-assembly mechanism and provide theoretical support for their industrial applications.The present study first introduces the basic theory,calculation model,control equations and algorithm process of mesoscale Brownian dynamics simulation,to lay foundation for the subsequent numerical simulation calculations.And secondly,a reasonable calculation process is designed and the systematically study on the self-assembly behaviors of rodlike micelles is carried out to obtain the quantitative relationship of the undetermined parameters in the established differential equation and time under different solution conditions.It shows that the solution conditions,namely the concentration,temperature and shear rate,can promote and suppress the self-assembly behaviors of rodlike micelles at the same time.In other words,the proper solution condition promotes rodlike micelles to self-assemble,on the contrary,the exceeding high or low condition suppresses the self-assembly behaviors.Finally,the quantitative relationships of undetermined parameters and time obtained from mesoscale Brownian dynamics numerical calculation are introduced into the established differential equation to integrate it.The self-assembly model of rodlike micelles can be established by simplifying and inductive reasoning the integrated equation,to predict the self-assembly length of rodlike micelle under different solution conditions.The verifying results show that the model can qualitatively predict the self-assembly degree of rodlike micelles.