Morphology of lithium-containing diblock copolymer thin films

The morphology of block-copolymer, ion-conductive, electrolyte thin films is studied. Based on PS-b-PEO and the alkali salt Li[N(CF₃SO ₂)₂], hybrid structures are probed as a function of Li/PEO ratio. Using optical microscopy, AFM and grazing incidence SAXS, films of 50 nm thickness are probed right after spin-coating. Below a critical Li/PEO weight ratio of 0.015, the crystallization of PEO is prohibited and nanostructured block copolymer films with Li incorporated in the PEO domains are obtained. In the range of 0.015 > Li/PEO > 0.035, aggregation of Li salt on the polymer film surface occurs. Solvent-vapor annealing of such films further enriches the Li salt at the surface. For Li/PEO > 0.035, the electrolyte films become unstable and dewet on the surface of the silicon substrate.(Figure Presented)