Dynamics Simulation Of The Self-assembly Of Amphiphilic Block Copolymers And Nanoparticles In Solution

The self-assembly of amphiphilic block copolymers in solution is a facile and popular method for the preparation of aggregates of controllable morphologies,such as spherical micelles,disk-like micelles,cylindrical micelles and vesicles.Nanoparticles exhibit advantageous electrical,optical,or magnetic properties,and they can be selectively located within different parts of aggregates.The co-assembly of block copolymers and nanoparticles has opened pathways for engineering flexible composites,which may lead to promising applications in drug delivery,surface-enhanced Raman spectroscopy,highly sensitive biosensor,bio-imaging probe and high-density data storage.In this thesis,we implement the dissipative particle dynamics approach to study the coassembly of linear amphiphilic diblock copolymers(AB)and nanoparticles(P)/polymer-coated nanoparticles P(B_nA)_m in dilute solutions.We focus on the selective localization of nanoparticles within vesicle walls.Then we investigate morphologies formed by amphiphilic cyclic brush block copolymers in dilute solution,discuss how the backbone asymmetry and graft asymmetry influence the self-assembly behaviors of amphiphilic cyclic brush copolymers,and elaborate the formation mechanisms.The main achievements of this dissertation are summarized as follows.1.For the P+AB system,the aggregation morphology and the distributions of nanoparticle within vesicle walls depend greatly on the hydrophobic block length,hydrophobic bead-solvent repulsive interaction,and nanoparticle concentration.In this system,we find that the aggregation morphology can be changed from rod-like micelles to disk-like micelles and further to vesicles by controlling the nanoparticle concentration and the interaction parameter between the hydrophobic blocks and the solvents.The ratio of the hydrophobic/hydrophilic block and the nanoparticle concentration largely affects the structural characteristics of vesicles and the dispersion of nanoparticles.Copolymers with a longer hydrophobic block length are more likely to form vesicles with a smaller aqueous cavity size and vesicle size as well as a thicker wall.At the same time,the nanoparticles in the hydrophobic membrane tend to locate closer to the center of the vesicle and they become more compactly organized.A significant discovery is that the larger the nanoparticle concentration,the smaller the aqueous cavity and the larger the vesicle size.We can also locate the nanoparticles at the center of spherical micelles or the hydrophobic membranes of vesicles by varying the nanoparticle concentration.2.For the P(B_nA)_m+AB system,the distributions of nanoparticles within vesicle walls can be well manipulated.Dependent on the number of nanoparticles,the grafted hydrophobic chain length and the tethered arm number,copolymers can form a rich variety of morphological structures including Momordica charantia L.Var.abbreviata Ser.-like vesicles,multicavity vesicles,vesicles and bilayers.The tethered arm number affects the dispersity of the nanoparticles in the angular direction of the vesicle walls.With the increase of the tethered arm number,the nanoparticles change from aggregation to dispersion.On the basis of a quantative analysis model,we find the radial distributions of the nanoparticles can be precisely controlled by changing the grafted hydrophobic chain length.As the grafted hydrophobic chain length increases,the nanoparticles move from the vesicle surfaces to the center of the vesicles so that the tethered arms can be extended to both the inside and the outside interfaces rather than all point to the outside interfaces.The tethered arms are more likely to extend to the outside interfaces than that to the inside interfaces,for the steric reason.In addition,the nanoparticles can be localized in the central 20%of the vesicle walls in a specific circumstance,which is in excellent agreement with the experimental results of Mai and Eisenberg’s.These studies provide the experimentalists with a way to design carrier-assistant drug delivery systems,which can improve the encapsulation efficiency,realize the specific targeting,and control the release of drug.3.For the amphiphilic cyclic brush copolymers system,engineering of the backbone asymmetry and graft asymmetry can be used to control the resultant supramolecular architectures.Six distinct types of aggregates are observed in the cases of fixed backbone length and different side chain length,including rods,plates,vesicles,large compound vesicles,bilayers,and spheres.With fixed solvophilic/solvophobic backbone lengths and solvophobic side chain length,the corona volume fraction increases as solvophilic side chain length increases,and more curved interfaces are formed,leading to a morphological transition from vesicles to plates,rods and finally to spheres.With fixed solvophilic side chain length,the thickness of the plate becomes larger while its width becomes narrower as the solvophobic side chain length increases,and plates turn into spheres.Compared to its bottlebrush analogues,amphiphilic cyclic brush copolymers tend to form plate with thinner thickness and broader width because of the topological constraint due to the ring architecture.For spheres,with fixed solvophilic side chain length,the number of spheres decreases,the micelle core radii/the radii of gyration of the spheres increase and the corona thicknesses of these spherical micelles decrease as the solvophobic side chain length increases.Under the same conditions,the graft asymmetry of amphiphilic cyclic brush copolymers is higher than that of their bottlebrush analogues.Cyclic brush copolymers can easily form compact and stable nanomicelles.We suppose this work could inspire researchers to design structurally complex functional material with broad applications,such as sensing,bioimaging,drug delivery,photoacoustic imaging and photothermal/photodynamic therapy.