Self-assembly of diblock copolymers for engineering applications

Diblock copolymers (BCPs) are very useful materials that can phase-separate to form a variety of highly ordered nanostructures. The lamellar structure and the gyroid structure get special attention due to their potential applications in the lithographic patterning and membrane separation processes, respectively. Devices made of microelectronics have become an essential part of our lives. The continuous improvement that we enjoy in microelectronics is greatly owing to progress in the photolithographic patterning technique. Photolithography has enabled shrinking the feature size in microelectronics, but it has reached a resolution limit of ~ 40 nm half-pitch. Therefore, development of higher-resolution patterning techniques is required to enable manufacturing next-generation microelectronics. Directed self-assembly (DSA) of lamella-forming BCPs offers one promising approach. Microdomains with sub-10 nm half-pitch can be readily obtained using high χ silicon-containing BCPs. The continuing demand for decreasing the feature size provided the motivation to synthesize, characterize and utilize BCPs with sub-5 nm half-pitches for making DSA patterns. Scarcity of clean water resources has become a global challenge. Membrane separation technology provides an efficient and low-cost approach to producing clean water. The increasing demand for clean water requires improvements in current membranes. Membranes made from BCPs are believed to offer a path to both high permeability and high selectivity due to their high porosity and narrow pore-size distribution. A porous gyroid structure has continuous pore channels that span the entire thickness of BCP layer without alignment. Therefore, self-assembly of gyroid-forming BCPs is a particularly attractive approach to creating water ultrafiltration membranes with improved performance. In this work, lamella-forming BCPs with sub-5 nm half-pitch microdomains were synthesized and their orientation behaviors in thin films using the bottom and top surface treatments were investigated. The perpendicular lamellar structure was obtained and the line-space DSA pattern was demonstrated. A synthetic process was established to reproducibly make gyroid-forming BCPs with different χ values. Gyroid composite membranes were made from one of the gyroid-forming BCPs by a newly developed process. The performance of these gyroid composite membranes for water ultrafiltration was tested. The membrane provides a proof of concept demonstration of high permeance and a molecular weight cut-off.