Microphase separated structures of block copolymer thin film with non-volatile selective solvent

Microphase separated structures of block copolymer, polystyrene-b-polyisoprene (PS-b-PI, PS = 14%) including non-volatile selective solvent thin films were investigated using grazing incidence small angle X-ray scattering technique. The diethyl phthalate (DEP) was used as a non-volatile selective solvent which solves PS only. The DEP swelled PS phase selectively and the microphase separated structure transited from the PS spherical domain to the lamellar domain with an increase in DEP content in the bulk state. Similarly, the phase separated structure in the thin film prepared by spin cast on a silicon wafer from the mixture of toluene/DEP and block copolymer changed according to the initial DPE concentration. However, the morphologies developed in the thin film were shifted to the structures at lower DEP concentration than that expected from the initial concentration. Moreover, the cylindrical and lamellar domains were aligned parallel and perpendicularly to the substrate, respectively.