Cylindrically Confined Diblock Copolymers

Lamella-, cylinder-, and sphere-forming block copolymers (BCPs) of polystyrene-b-polybutadiene (PS-b-PBD) were drawn into the pores of anodized aluminum oxide (AAO) membranes ill the melt by capillary forces. After thermal annealing, the nanorods of the BCP were removed 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 diameters of the pores in the AAO and the molecular weight of the block copolymers were varied to investigate the effect of confinement on the microphase separation of the 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. In addition, torus-like morphologies were observed as the degree of confinement increased. For the bulk cylinder-forming BCPs, a rich variety of morphologies, not seen in the bulk, were observed that included stacked torus-like morphologies and single-, double-, and triple-helical morphologies The specific morphology depended on D/L-0, where D is the AAO pore diameter and L-0 is the period of the BCP in the bulk. D/L-0 was varied from 0.92 to 2.22. For bulk sphere-forming BCPs, core-shell cylindrical morphologies, single columns of spherical microdomains, and spirals of doubly and triply paired spherical microdomains were observed. Transmission electron microscopy was also performed in tomography mode (TEMT) to quantitatively determine a 3-D description of the morphologies. The morphologies found were consistent with recent simulations of confined BCPs.