Monte Carlo Simulation Of The Self-assembly Behavior Of Amphiphilic ABA Triblock Copolymer In Selective Solvent

Monte Carlo simulation was used to study the behavior of the self-assembly of ABA amphiphiles triblock copolymers in selective solvent. Self-avoiding chains was carried out in a simple cubic lattice system with 40*40*40 sites. The periodic boundary condition was applied in all three directions. In this thesis, the behavior of the self-assembly of amphiphiles triblock copolymers was studied in terms of the following two aspects.Firstly, amphiphilic copolymers can spontaneous self-assemble into ordered micelles in selective solvent. The micelle morphology is a function of the properties of solvent. This behavior can be used in drug delivery, and becomes a very important topic. In this thesis, Monte Carlo simulation was used to study the effect of the solvent's properties on the micelle structure for the ABA amphiphiles triblock copolymers. The results showed that the micelle morphology changed from spheres to rods and then to vesicles by increasing the solvent solubility, which is in good agreement with the experiment. Moreover, we studied the distribution of the fraction of the chain number with the end-to-end distance. The results indicated that the amount of folded chains is almost the same as that of stretched chains in the vesicle. Although most chains are folded, stretched chains can be found in the rod and sphere micelles. The study not only provides a facile way to control the morphology of micelles, but also gives an insight into the micelle structures on microscale.Secondly, although great effort has been devoted to study the formation of vesicles both theoretically and experimentally, the lack of the understanding on the pathways of spontaneous vesicle formation of amphiphilic molecules is still a big problem in the study of vesicles. We studied the pathways of spontaneous vesicle formation of the ABA triblock copolymers in selective solvent by Monte Carlo simulation. The simulation provided the detail vesicle formation process for the ABA amphiphiles triblock copolymers in selective solvent. It is revealed that the vesicle formation pathway strongly depends on the annealing speed. Moreover, we can not use one pathway to describe the spontaneous vesicle formation process even though for the same system and condition. Hydropholic molecules diffusing in spherical micelles and oblate membrane closing may coexist for vesicle formation.