Multidimensional Morphology Control for PS-b-P-4 VP Templated Mesoporous Iron (III) Oxide Thin Films

Mesoporous alpha-Fe2O3 thin films with large area homogeneity demonstrate tremendous potential in multiple applications. In the present work, the synthesis of morphology-controlled alpha-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 Delta chi value of around 0.77.

Automated summary

Mesoporous alpha-Fe2O3 thin films with large area homogeneity show great potential in various applications. In this work, morphology-controlled thin films were synthesized using PS-b-P4VP diblock copolymer assisted sol-gel chemistry. By adjusting the solvent type and polymer-to-FeCl3 ratio, the morphology of the thin films can be systematically tuned, leading to different nanocluster structures and porous formations. Adjusting the solvent selectivity in DMF/1,4-dioxane solvent mixtures also results in a transition from spherical to wormlike pore shapes.