Self-assembly Of Diblock Coplymer And Condensation Of Polymer Chain

Under certain external environments, block copolymers can self-assemble into novel and functional materials in nano-scale. The research on new materials greatly promoted the development of polymer theory and polymer applied science, which also attracted the attention of scientists in fields of chemistry, physics, materials science, life science, environmental science and other fields. The studies on the self-assembly of block copolymers suffer the inductions from confinement, nanoparticles, shear flow, and selective solvent, can promote the understanding of intrinsic characters of block copolymers segregation. In this dissertation, we use dissipative particle dynamics (DPD) method, self-consistent field theory (SCFT) calculations and molecular dynamics (MD) methods studied the self-assembly of the following systems:the mixtures of cylindrical forming diblock copolymers (DBCPs) and diblock nanorods (DNRs), DBCPs under spherical shell confinement, spherical polymer brush under good solvent, and the mixtures of DNA and multivalent cations.In Chapter2, we perform dissipative particle dynamics (DPD) simulation to study the co-self-assembly of polymers containing amphiphilic diblock nanorods (DNRs). In the cylinder-forming A3B7DCPs/DNRs system, we find that the cylinder phase can be destroyed by a few DNRs additives and then a stable lamellar phase is rebuilt when sufficient DNRs in the system. However, in the lamellar-forming A5B5DCPs/DNRs system, the lamellar morphologies are always sustained in spite of the number of DNRs. We also find that the lamellar spacing is different in the two kinds of lamellar phases. On the other hand, Orderly layered structures of the DNRs have been observed in both the systems. Furthermore, the orientations of DNRs have close relationships with the number of DNRs and the type of DCPs. Last, we investigated the homopolymer A10and DNRs blend, and find that the DNRs prefer to aggregate together in this system.In Chapter3, the topic of self-assembly of cylinder-forming diblock copolymers (DBCPs) under spherical shell confinement in different surface fields is explored using real-space self-consistent field theory (SCFT) calculations. Using this approach we observed various microstructures of cylinder-forming DBCPs at different confinement dimensions and surface fields. From detailed searching for the microdomain morphologies, an obvious conclusion is that the interactions between the confinement surface and the polymers have a great effect on the self-assembly. Most of the microstructures are unique and not reported in bulk or under planar and cylindrical confinements.In Chapter4, a coarse-grained model for an elastic shell grafted with polymer chains is investigated by molecular dynamics (MD) methods. With increasing the number of grafted polymer chains (GPCs), it is found that the conformation of the shell undergoes from expansion to collapse and back to the expansion. By varying the density of the GPCs, the phase transition of the elastic shell can be successfully controlled at moderate bending energy of the shell and at moderate binding energy between the shell and GPCs. Furthermore, the self-assembly structures of the GPCs are also affected by the elastic shell in certain conditions.In the case of a few GPCs on the shell, the chains tend to be adsorbed on the shell surface unfolded at high value of bending energy. However, when the bending energy is small, the chains can be folded several times easily. This may be an important step towards a deeper understanding of how to control the microstructure in the production of bio-composites.In Chapter5, condensation of DNA induced by spermine is studied by atomic force microscopy (AFM) and molecular dynamics (MD) simulation. In each experimental group, the equivalent amount of multivalent cations is added to the DNA solutions with different times. We find that the process of DNA condensation strongly depends on the speed of adding cations. Namely, the slower the spermine cations are added, the slower the DNA collapse. The MD and SMD simulations results agree well with those experimental results, and the simulation data also shows that the more the times of adding multivalent cations is, the more compact the condensed DNA structure is. This investigation can help us to control DNA condensation and understand the complicated structures of DNA-cation complex.