Multidimensional Morphology Control for PS‐b‐P<sub>4</sub>VP Templated Mesoporous Iron (III) Oxide Thin Films
Shanshan Yin, Wei Cao, Qing Ji, Yajun Cheng, Lin Song, Nian Li, Christian L. Weindl, Matthias Schwartzkopf, Stephan V. Roth, Peter Müller‐Buschbaum
Abstract
Abstract Mesoporous α‐Fe 2 O 3 thin films with large area homogeneity demonstrate tremendous potential in multiple applications. In the present work, the synthesis of morphology‐controlled α‐Fe 2 O 3 thin films is realized with polystyrene‐block‐poly(4‐vinyl pyridine) (PS‐b‐P 4 VP) diblock copolymer assisted sol‐gel chemistry. The solvent category (DMF and 1,4‐dioxane) and polymer‐to‐FeCl 3 ratio used for the solution preparation are systematically varied to tune the morphology of the thin films. For both solvents, DMF and 1,4‐dioxane, nanocluster structures are obtained with low PS‐b‐P 4 VP concentration. When the concentration of PS‐b‐P 4 VP reaches the critical micelle concentration, spherical and wormlike porous structures are specifically formed in the DMF and 1,4‐dioxane solvent system, respectively. Further increasing the polymer‐to‐FeCl 3 ratios leads to the enlargement of the spherical pore sizes in the DMF system, whereas the center‐to‐center distances of the wormlike structures in the 1,4‐dioxane system decrease. Moreover, DMF/1,4‐dioxane solvent mixtures with different volume ratios are applied for the sol–gel solution preparation to gain more insight into how the solvent selectivity affects the thin film morphology. By adjusting the preferential affinity of the solvent mixture to the polymer blocks, a spherical to wormlike pore shape transition is observed with a critical Δ χ value of around 0.77.