Cylindrically confined diblock copolymers
The autonomous organization of components into patterns or structures without human intervention is known as self-assembly. This process is common throughout nature and technology and may involve many different kinds of interactions. This thesis treats the self assembly of block copolymers (BCPs) confined within cylindrical nanopores and generation of novel structures resulting from the constraints of size and forced curvature. Lamella-, cylinder-, and sphere-forming BCPs were drawn into the pores of anodized aluminum oxide (AAO) membranes in the melt phase by capillary forces. After thermal annealing, BCP nanorods were isolated by dissolution of the AAO with a weak acid and transmission electron microscopy (TEM) was used to investigate the resultant morphologies of the confined BCPs. The diameter and surface chemistry of AAO nanopores and molecular weight of BCP were varied to investigate the effect of confinement on the microphase separation of BCP. Concentric cylinders were observed for the lamella-forming BCPs under 2D confinement and deviations of the lamella repeat period were measured as a function of AAO pore diameter.
For the bulk cylinder-forming BCP, a rich variety of morphologies, not seen in bulk, were observed that included stacked discs, toruses, single, double and triple helices and helices with a cylinder in the core. The specific morphology observed depended on D/Lo, where D is the pore diameter and Lo is the period of the BCP in the bulk. Electron tomography was performed on the cylinder-forming BCP to obtain 3D image of the confined morphology.
For bulk sphere-forming BCP, novel structures, such as core-shell cylinders and spiraling rows of single, double and triple paired spherical microdomains were observed. The bulk cylinder-, and sphere-forming BCP were also placed in silane modified AAO and a rich variety of novel structures were observed. Inside silane modified AAOs, the preference of the blocks towards the pore wall was also altered. The results of cylinder-forming BCP were consistent with the results from the simulations. This method offers and exciting opportunity to manipulate the phase separation of BCPs and discover the novel periodic structures that are significantly different from those observed in bulk.