Dynamic Evolution Of Vesicle Formed By Complex Amphipathic Block Copolymer Is Studied By Computer Simulation

The structures,such as rod-like micelles,circular micelles,pie micelles,segmented micelles,monolayer vesicles,multilamellar vesicles,Janus vesicle,of complex amphiphilic block copolymers system self-assembed are rich and colorful.They have the potential to be widely used in drug delivery and release,microelectronics,preparation of nano materials with controllable size.In this paper,the self-assembly behavior and self-assembly structures of complex amphiphilic block copolymers system are studied by using dissipative particle dynamics method(DPD).Meanwhile,the formation mechanism and kinetic evolution of vesicles are clarified.The major work and conclusions of the thesis are as follows:The DPD method is performed to investigate the spontaneous formation and fusion of onion shape vesicle from(A6(B2)3)type comb-like block copolymers.Our results show that comb-like block copolymers may be a good candidate for onion shape vesicle formation.The spontaneous fusion dynamics between the onion shape vesicles are studied,and the fusion process can be characterized as two parts:the outer and inner membrane fusion.However,both the two parts have similar fusion dynamics which coincide with that observed in vesicles formed of linear diblock copolymers.In addition,the mixture systems containing amphipathic linear and comb-like block copolymers are investigated in dilute solution.By systemically varying the amount of linear block copolymers and the bond angle potential of hydrophobic blocks,we construct a diagram to indicate the thermodynamically stable region,in which irregular vesicle,tubular vesicle,spherical vesicle,rod-like and toroidal micelle are observed.Nevertheless,no different about the vesicles fusion dynamic is found.The main reason may be attributed to the molecular structures which possess the same hydrophobic but different hydrophilic block.The self-assembly of comb-like block copolymer grafted nanoparticle(PA2n(B2)n)is studied by DPD method in different selective solutions.By systemically changing the interaction force between nanoparticle and other particles,we construct three thermodynamic stable regions,in which lamellar micelle,spheres micelle,axiolitic micelle,columnar micelle,segmented lamellar micelle,regular onion shape micelle,irregular onion shape micelle,regular segmented rod-like micelle,and vesicle are discovered.Meanwhile,the dynamic formation processes of several special structures are explored.Finally,it is found that the interaction force between particles plays an important role in morphology of aggregates and the distribution of nanoparticles in micelles.The DPD method is employed to study the formation,fusion,and fission pathways of vesicles from comb-like block copolymer grafted nanoparticle(PA2n(B2)n).Our results show that comb-like block copolymer tethered nanoparticles can self-assemble into stable vesicles,which may be a good candidate for drug entrapment and controlled release of drug.The spontaneous fusion of this type vesicle has been studied,whose mechanism is different from the vesicles formed by comb-like block copolymers.However,the fission mechanism is similar.In addition,we find the sizes of vesicle have an assignable effect on fission mechanism,when there is a big size gap between two vesicles,a micelle will directly fall off from the parent vesicle.The fusion and fission processes always experience the congregation of nanoparticles,which could be attributed to the nature of nanoparticles.The large and rigid nanoparticles inevitably result in changes of surface tension of the vesicle,which is a key factor influencing the membrane dynamics.The coarse grained method is employed to structure three dendritic macromolecules(RH,RF,RHF),and the dynamic mechanism of vesicle from the mixed self-assembled of RH,RF,RHF is simulated by using DPD method.By changing the content of RHF with the equal content of RH and RF in the mixed system,we obtain three kinds of vesicles,which are Janus vesicle,stratified vesicles and symmetrical vesicles.We explore the self-assembly mechanisms of different structure vesicles in detail.The results show that the content of RHF leads to different assembly modes of RH and RF in the solution,which results in the different membrane structure of vesicle.In addition,we find that the length of hydrophobic chain of dendritic macromolecules directly determines the wall thickness of vesicle.