Spontaneous Formation of Nanopores and Nanorings in a PS-b-PEO Block Co-Polymer

PS-b-PEO block co-polymers have been reported to form cylindrical, lamellar, gyroidic, and supramolecular architectures due to several reasons: some of the reasons include the chemical incompatibility between the lipophilic and lipophobic covalently cross-linked blocks resulting in a high Flory-Huggins interaction parameter, the annealing solvent, and the interfacial boundary conditions between the substrate and the phase separating blocks. We report here for the first time on the spontaneous formation of nanopores and nanorings in PS-b-PEO block co-polymers. The mean size and depth of the pores are about 150nm and 40nm, respectively, while the pores occur randomly placed in clusters of about 2-5 pores. The pore clusters leave behind a breath-like architecture replicated by the phase separating block co-polymer. These breath architectures, in the shape of nanorings, are formed during the initial period of phase separation and do not disappear after phase separation has been achieved, leaving behind a PS-enriched circular framework. The diameter of the nanorings is in the 200-700nm range, as measured from AFM phase and height images. This range falls within the reported size of water droplets forming breath structures on polymer films. The resulting nanoarchitectured materials could find potential applications where biocompatibility and water permeability of the PEO block within the nanopores is desirable. In addition, the slightly elevated nanorings could also provide semi-enclosed barriers that can serve as micro/nano-enclosed cell and tissue cultures.