The difference of PMMA‐brush‐modification on the oxygen permeable perovskite‐type oxides by consisting elements

Abstract

AbstractOxygen permeation of perovskite‐type ceramics consists of three elementary processes: oxygen absorption, bulk oxygen diffusion, and oxygen desorption. In most cases, the rate‐determining step is the oxygen diffusion step, and the use of thin films improves the oxygen permeation rate of perovskite‐type ceramics. Polymer‐brush‐modification is a useful technique to produce thin films. Grafted PMMA‐brushes exhibit a screening effect for attractive interactions between core ceramic particles, thereby inducing repulsive forces on them. This results in the formation of a densely packed ordered array. Modification of the polymerization‐initiator and polymer‐brushes should affect the oxygen permeation properties of the ceramic particles, especially surface oxygen adsorption and desorption. In this paper, it is demonstrated that these modifications change the cation chemical states and lower the oxygen desorption rate, while increasing the desorption peak temperature. The surface of La–Sr–Co–Fe perovskite‐type oxides was modified only with the polymerization initiator, (2‐bromo‐2‐methyl)propionyloxyhexyltriethoxysilane (BHE) because there is no direct interaction between the polymer‐brush and the substrate, while the initiator is directly modified to the substrate. The oxygen desorption behavior of BHE‐modified oxides indicates that its oxygen desorption property is impeded without modification with PMMA. The investigation of BHE‐modified oxide cation chemical states and oxygen desorption behaviors imply that the BHE‐modifying site and change in chemical states have selectivity depending on cation species. Although sintering causes the formation of silicate and ceramic decomposition, this step can eliminate the harmful effects of BHE‐modification in total. When conventional La–Sr–Co–Fe perovskite‐type ceramics are used, sintering is preferable for the recovery of thin‐film surface reactions. However, if we utilize site selectivity of BHE‐modification, the harmful effects of those modifications can be avoided by modifying BHE onto sites that hardly participate in surface reactions.