Multidimensional Morphology Control for PS-b-P₄VP Templated Mesoporous Iron (III) Oxide Thin Films

Mesoporous α-Fe₂O₃ thin films with large area homogeneity demonstrate tremendous potential in multiple applications. In the present work, the synthesis of morphology-controlled α-Fe₂O₃ thin films is realized with polystyrene-block-poly(4-vinyl pyridine) (PS-b-P₄VP) diblock copolymer assisted sol-gel chemistry. The solvent category (DMF and 1,4-dioxane) and polymer-to-FeCl₃ 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-P₄VP concentration. When the concentration of PS-b-P₄VP 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-FeCl₃ 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 Δχ value of around 0.77.