Network formation, as a result of polymerization and crosslinking, induces drastic change in properties of polymeric materials. Several significant applications of the property alteration can be seen in advanced lithographic nanofabrication. In spite of the significant roll in such applications, it is still not so easy to elucidate the precise reaction dynamics in polymeric materials because of the micro-heterogeneous nature in polymer solids. High-precision single-molecule tracking (SMT) of guest fluorescent molecules can be a powerful approach for the evaluation of microscopic inhomogeneity in host polymer solid at a temperature higher than the glass transition temperature (Tg) because diffusional motions of individual guest molecules are strongly affected by their local environments [1, 2]. In the present study, we have tracked three-dimensional (3D) lateral motions of single guest molecules in polymer films on solid substrates by using so called the astigmatism imaging technique with an aim to evaluate the microscopic inhomogeneity in the sample including the effect of the interfaces. As samples, thin films of poly(2-hydroxyethyl acrylate) including perylenediimide (PDI) derivatives were prepared on glass substrates by spin-casting. Sequential fluorescence images of single PDI dyes in the polymer films were obtained by using a wide-field microscope. The lateral positions of individual PDI dyes on the lateral (XY) plane were localized by analyzing their fluorescence intensity with 2D Gaussian function, while their Z positions were determined from the elongation (X- and Y-widths) of the fluorescence intensities. A series of investigation using the 3D-SMT revealed that the guest PDI dyes in 1000-nm-thick films showed 2D motions on the XY plane and, their Z positions were 500-800 nm apart from the glass substrate. Most of the 2D motions on the XY plane were categorized as "normal" diffusion. On the other hand, their motions along the Z-axis were "confined" ones, which was confirmed by the mean-square-displacement (MSD) vs time plots. In our presentation at the meeting we will show results of different guest dyes and discuss about the mechanism of this unusual diffusion behavior. References: 1. S. Ito, T. Kusumi, S. Takei, and H. Miyasaka, Chem. Commun. 2009, p6165. 2. S. Ito, K. Itoh, S. Pramanik, T. Kusumi, S. Takei, and H. Miyasaka, Appl. Phys. Express 2009, 2, 075004.

3D tracking of single guest molecules in polymer thin films toward the investigation of complex dynamics in micro-heterogeneous media

250th National Meeting (2015)

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