Drop-Cast Hybrid Poly(styrene)-b-Poly(ethylene oxide) Metal Salt Films: Solvent Evaporation and Crystallinity-Dependent Evolution of Film Morphology

Morphology templates of solution–based diblock copolymer (DBC) films with loading metal salts are widely applied in photocatalysts, photovoltaics, and sensors due to their adjustable characteristics based on surface (de–)wetting and microphase separation. The present work investigates the morphologies of drop–cast hybrid films based on poly(styrene)–b–poly(ethylene oxide) (PS–b–PEO) and the metal salts titanium isopropoxide (TTIP) and zinc acetate dehydrate (ZAD) in comparison to the pure DBC. By utilizing scanning electron microscopy, grazing–incidence small– and wide–angle X-ray scattering, and differential scanning calorimetry, we find that the resulting film morphologies depend not only on the presence of metal salts but also on solvent evaporation and crystalline formation. At 20 °C, additional TTIP and ZAD in the polymer template cause the morphology to change from packed globular structures to separated wormlike structures attributed to the changed polymer environment. Furthermore, additional tetrahydrofuran causes irregular structures at the precursor film part and the overlapped wormlike structures to transition into close–packed globular structures at the cap film parts of the pure DBC. In contrast, at 50 °C, the globular structures transit to fingerprint patterns due to the thermal behavior of the crystallizable PEO blocks, and the metal salt additives suppress crystalline structure formation in the PEO domains.