Abstract
AbstractMesoporous 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.
Highlights
Hematite (α-Fe2O3), as the most common iron oxide polymorph, is characterized by its abundance, nontoxicity, good assembly of block copolymers.[2,20,26,27,28,29,30] Typically, nanopatterning of the Fe2O3 NPs through block copolymer templates can be categorized into two types: directly accommodating the NPs inside the block copolymer matrix or in situ reducing thermodynamic, and chemical stability as well as large block copolymer coordinated metal precursors into NPs
For tracking the successive morphology evolution with respect to the solubility parameter of a solvent, we study DMF/1,4-dioxane solvent mixtures with different compositions at a fixed ωPS-b-P4VP:ωFeCl3 ratio of 2:1 for the sol-gel solution preparation
When the ωPS-b-P4VP:ωFeCl3 ratio used for sol-gel solution preparation is 1:2, nanocluster structures are observed in both DMF and 1,4-dioxane solvent
Summary
Hematite (α-Fe2O3), as the most common iron oxide polymorph, is characterized by its abundance, nontoxicity, good assembly of block copolymers.[2,20,26,27,28,29,30] Typically, nanopatterning of the Fe2O3 NPs through block copolymer templates can be categorized into two types: directly accommodating the NPs inside the block copolymer matrix or in situ reducing thermodynamic, and chemical stability as well as large block copolymer coordinated metal precursors into NPs. The formation of thermodynamically stable block polymer micelles is mainly governed by the following three contributions: The stretching degree of the core-forming polymer chains, the interfacial tension between the micelle core and the surrounding solvent, and the repulsive interactions among corona-forming chains.[25] The first two contributions can be affected by factors including copolymer composition and concentration, poor solvent content in the solution, and the preferential affinity of the common solvent.[36] The third contribution mainly refers to block polymers, which contain ionized chains during micellization. Based on the multidimensional characterization results, the underlying mechanism for governing the structural evolution of the thin films is revealed
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