| Block copolymer self-assembly has been receiving considerable attention for many decades because it can lead to a variety of morphologies by simply controlling the thermodynamics of the system without the need of external forces. The self-assemble aggregates, as known as micelles, provide highly potential applications in nanotechnologies such as data storage devices, electrical and magnetic devices, biomedical purposes, energy conversion and storage and filtration membranes. Although there is a vast literature on block copolymer melt and dilute system, less work has been done for concentrated solutions. At higher concentrations, block copolymers in a selective solvent form lyotropic mesophases which possess a finite yield strength. Depending on the degree of ordering and entangling, block copolymer concentrated solutions can exhibit different mechanical properties.;This thesis is organized into two sections: The first section starts with a brief introduction of the mechanism of micelle formation (Chapter 1). Then the self-assembly behavior of a diblock copolymer in a selective solvent was examined (Chapter 2). The phase diagram of this system was first determined by mean-field theoretical calculations in which we proposed fcore, the total volume fraction of the core, as the most important factor for controlling phase boundaries in concentrated solutions. Complementary experiments were carried out to compare with the theoretical work. A second investigation for the same polymer system (Chapter 3) looked at the effect of initial alignment on micelle ordering near the order-disorder transition temperature, which may provide an effective way to identify the optimum annealing temperature range to achieve macroscopic alignment.;The second section of the thesis investigated the confinement effect on block copolymer phase behavior. That is, when the block copolymer is confined in an environment which has a dimension comparable to the characteristic period of the polymer domains, novel morphologies can be attained which are not accessible in the bulk or thin film system. The first half (Chapter 4) introduces the techniques we used in the following chapter and confinement effects. The second half (Chapter 5) explored 2D confinement effect on poly(styrene)-poly (isoprene)-poly(styrene) triblock copolymers by utilizing coaxial electrospinning techniques. The resultant structures were examined by in-situ X-ray scattering and electron microscopies. |
