Highly Ordered Nanoporous Thin Films by Blending of PSt-b-PMMA Block Copolymers and PEO Additives as Structure Directing Agents.
Herein, we present a simple method for producing nanoporous templates with a high degree of lateral ordering by self-assembly of block copolymers. A key feature of this approach is control of the orientation of polymeric microdomains through the use of hydrophilic additives as structure directing agents. Incorporation of hydrophilic poly(ethylene oxide) (PEO) moieties into poly(styrene-b-methyl methacrylate) (PSt-b-PMMA) diblock copolymers gives vertical alignment of PMMA cylinders on the substrate after solvent annealing. Because of the miscibility between PEO and PMMA, PEO additives were selectively positioned within PMMA microdomains and by controlling the processing conditions, it was found that ordering of PSt-b-PMMA diblock copolymers could be achieved. The perpendicular orientation of PMMA cylinders was achieved by increasing the molecular size of the PEO additives leading to an increased hydrophilicity of the PMMA domains and consequently to control the orientation of microdomains in PSt-b-PMMA block copolymer thin films.