Understanding Physicochemical Mechanisms of Sequential Infiltration Synthesis toward Rational Process Design for Uniform Incorporation of Metal Oxides

Abstract

Sequential infiltration synthesis (SIS) is a novel technique for fabricating organic–inorganic hybrid materials and porous inorganic materials by leveraging the diffusion of gas-phase precursors into a polymer matrix and chemical reactions between the precursors to synthesize inorganic materials therein. This study aims to obtain a fundamental understanding of the physicochemical mechanisms behind SIS, from which the SIS processing conditions are rationally designed to obtain precise control over the distribution of metal oxides. Herein, in situ FTIR spectroscopy was correlated with various ex situ characterization techniques to study a model system involving the growth of aluminum oxides in poly(methyl methacrylate) using trimethyl aluminum (TMA) and water as the metal precursor and co-reactant, respectively. We identified the prominent chemical states of the sorbed TMA precursors: (1) freely diffusing precursors, (2) weakly bound precursors, and (3) precursors strongly bonded to pre-existing oxide clusters and studied how their relative contributions to oxide formation vary in relation to the changes in the rate-limiting step under different growth conditions. Finally, we demonstrate that uniform incorporation of metal oxide is realized by a rational design of processing conditions, by which the major chemical species contributing to oxide formation is modulated.

Conductive Polyaniline–Indium Oxide Composite Films Prepared by Sequential Infiltration Synthesis for Electrochemical Energy Storage

“…The depth profiles revealed that the InO x phase was present down to the bottom of the PANI film, although the In concentration gradually decreased along the film thickness. The distribution of the metal oxide in the polymer matrix in SIS is closely related to the infiltration kinetics of the precursors and the reactivity between the precursors and specific functional groups of the polymer . As PANI does not contain precursor-reactive functional groups such as CO, as in poly­(methyl methacrylate), the spatial distribution of InO x in PANI is likely dominated by the temporal presence of TMIn molecules in the free volumes of PANI.…”

“…Sequential infiltration synthesis (SIS) is one of the subcategories of atomic layer deposition (ALD), and it has recently emerged as a promising way to prepare organic–inorganic composite films with excellent control over their morphologies. − The following are the major SIS growth mechanisms: (1) precursor infiltration into the polymer matrix; (2) reversible/irreversible reaction of the precursor with specific functional groups of the polymer; and (3) chemical reactions between precursors and coreactant precursors within the polymer matrix. − Various compositional and structural factors of the composite films, such as the ratio of organic-to-inorganic components and the distribution of the chemical composition, can be controlled by varying the SIS conditions, such as the growth temperature, precursor exposure time, and precursor purge time . Therefore, SIS is expected to be useful for preparing CP-MO composites with the content and distribution of MO carefully controlled.…”

Sequential Infiltration Synthesis with Organic Co-reactants for Extensively Swollen Organic–Inorganic Hybrid Thin Films

“…We extracted the absolute intensities of the major IR modes by fitting and subtracting the background signal, as explained in the Supporting Information (SI) (Figure S2). The absolute intensities of the bleached pristine modes are a measure of the concentration of each functional group consumed by the reactions with TMA. − Figure d shows the absolute intensities of the pristine C=O modes in the PMMA samples, which appeared as a negative peak owing to the consumption of the modes. As shown in Figure d, the consumption of the pristine C=O mode is larger in the PMMA-BDO sample than in the PMMA-H 2 O sample at later SIS cycles (>10th cycle), indicating that a greater number of TMA molecules reacted with C=O, probably due to the enhanced infiltration of TMA.…”

“…The saturated thickness increase in H 2 O-SIS is due to the formation of a dense layer of aluminum oxides/ hydroxides near the polymer surface, which acts as a barrier for TMA infiltration into the composite film at later cycles. 17 In contrast, the incorporation of long and flexible chains of BDO molecules may induce additional swelling of the polymer matrix. The incorporated BDO may create more and/or larger free volumes in the composite films, which may act as a diffusion pathway for the TMA molecules.…”

“…The C=O functional group (1738 cm −1 ) and C−N functional group (1589 cm −1 ) in PMMA and P2VP, respectively, are the preferred association sites for TMA, and the association reactions result in the bleaching (i.e., negative peaks) of the IR modes in the difference spectra, as shown in Figure 2b and c. 13,17,18 The association reactions are also related to the appearance of the shifted C=O and C−N modes in PMMA and P2VP, respectively; however, they are revealed in the TMA half cycles, not in the BDO half cycles (Figure S1). The blue-shift of the C−N peak that occurs as a result of the formation of a C−N•••TMA complex has been reported previously in SIS processes using TMA with P2VP.…”