Multidimensional Morphology Control for PS-b-P4VP 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

In this study, morphology-controlled α-Fe2O3 thin films were successfully synthesized using PS-b-P4VP diblock copolymer assisted sol-gel chemistry. Different solvent categories and polymer-to-FeCl3 ratios were systematically varied to tune the morphology of the thin films. The results show that solvent selectivity and polymer concentration play important roles in determining the morphology of the thin films.