Observation of molecular motions in polymer thin films by laboratory grazing incidence diffracted X-ray blinking

Abstract

AbstractResearch on polymer surfaces has shown that the mobilities of polymer chains, which affect the aggregation state and thus the physical properties of the material, differ between the surface and bulk. However, the mobilities of the surface polymers have not been fully characterized. Therefore, we propose a time-resolved method for evaluating surface mobility. This measurement scheme is called grazing incidence diffracted X-ray blinking (GI-DXB) and can be used to evaluate the molecular motions occurring at polymer surfaces by continuously measuring X-ray diffraction patterns near the total reflection angle over small time periods. In this study, the crystallized polymer poly{2-(perfluorooctyl)ethyl acrylate}(PC8FA) was measured. The decay constants, which are indexes of molecular motions, were calculated to be 3.98 × 10−3 s−1 for the fluoroalkyl groups in the side chains observed along the in-plane direction and 3.36 × 10−3 s−1 for the lamellar structure observed along the out-of-plane direction when 2000 diffraction profiles of 500 ms were recorded and the incident angle was 0.07°. In contrast, transmission DXB indicated decay constants of 2.63 × 10−3 s−1 for the side chains and 2.87 × 10−3 s−1 for the lamellar structures. These results suggested that the PC8FA surface is mobile, because a larger decay constant indicates a higher mobility. GI-DXB can be used to measure surface dynamics. The authors contend that GI-DXB is a highly versatile tool because it allows the evaluation of local motions with a laboratory X-ray system, and these motions cannot be detected by conventional surface analyses. This measurement scheme may facilitate the development of high-performance polymers and discovery of new physical properties.