Development Of Surfactant Adsorption Kinetics Model On The Interface Of Emulsion Droplets

Droplet size distribution which depends on the coalescence and breakage of emulsion droplets is an important index of the emulsion's performance,while surfactant plays a vital role in the droplets coalescence process.Through All-atom molecular dynamics simulation?AAMD?and Coarse-grained molecular dynamic simulation?CGMD?,the adsorption thermodynamics and kinetics of surfactant at sub-surface layer are studied.Through the coupling of CFD and MD simualtions at coalescence efficiency corrector C,the droplet size distribution inside a rotor-stator can be correctly predicted.By comparing with cases without MD coupling,it proves that the CFD-MD coupling scheme is an effective approach to predict the emulsion droplet size distribution inside a rotor-stator mixer.In CFD-MD coupling scheme,based on MARTINI force-field,the limiting diffusion coefficient of each surfactant is measured using Mean Square Displacement method?MSD?,and the Max.adsorption amount?_m of the surfactant at the water MCT-Oil interface is measured using successive monomer addition method.By setting up Cases with descreasing of shear rate,the influence of shear flow on adsorption kinetics,adsorption amount and monomer adsorption time are qualitatively analyzed.In order to study the adsorption kinetics of surfactant mixture,based on the premise that there are no strong interactions among different kinds of surfactants,coupling equation and verification equation which are proposed in this thesis can be used.The adsorption and desorption rate constants in coupling kinetics equation are equivelent to those in system with only one kind of surfacntat.Hence k_a,k_d of system with only one kind of surfactant are obtained.Take non-ionic surfactant TSP as an example,using least square fitting method to fit the monomer adsorption region,monomer adsorption rate constant and desorption rate constant could be obtained.What's more important,by using the parameter monomer adsorption ratio,the concentration in simulation and in experiment can be related.At last,this thesis deals with the unwanted lattice packing of W on the surface of anionic surfactant for Cases with shear rate lower than 10⁷ s^-1,which is caused by strong attraction between Ca?DBS?₂ and non-polarizable water W.The problem is similar to the freezing of water models of MARTINI-FF,which may be caused by lower perturbation in the system studied.To deal with this problem,three possible ways are proposed,and each method is analyzed in detail to validate its feasibility.