Theory of self-assembly of block copolymers: Effects of architecture, blending with homopolymers and shear

Similar to many self-assembling materials such as surfactants or liquid crystals, block copolymers undergo mesophase transitions due to the changes of external fields. This thesis focuses on the effects of copolymer architecture, concentration fields, and external shear flow fields on the self-assembly of block copolymers. Theories of the morphology transition of diblock copolymers at equilibrium have been studied for more than two decades. However, relatively little work has been done on more complicated architectures. The first part of this thesis uses a combination of the density functional theory (DFT) and the theory of composition fluctuations to examine the morphology transition in block copolymers of topologically distinct architectures. The morphology diagrams and corresponding properties are calculated for A-B-A triblock copolymer with given architectural parameters. The second part of this thesis focuses on the phase behavior of polymer blends consisting of amphiphilic block copolymers and selective homopolymer solvents. Phase diagrams are calculated for binary and ternary systems and the formation of induced morphologies due to the change of concentration fields are studied. The effects of architecture and sizes of constituent blocks of copolymers and the sizes of homopolymers are investigated by comparing various systems. Also, the critical Lifshitz point is examined and discussed. The third part of the thesis focuses on the order-disorder transition (ODT) and order-order transition (OOT) of block copolymers induced by an external shear flow field. The presence of shear alters the microscopic evolution of fluctuations and leads to a suppression of the fluctuation field. Consequently, the effective potential caused by excitations of monomer densities is reduced, resulting in an apparent increase of the ODT temperature. The self-consistent equation of the fluctuation spectrum is solved numerically, and the transition curve with respect to the applied shear rate is computed. This result resolves the recent controversy between experimental data and the previous perturbation analysis and shows good agreement with experimental results