Discovery of the bi-layered structure in spin-coated polyacrylamide films on the gold surface

The reflection-absorption Fourier transform infrared spectroscopy (RA-FTIR) with the polarized lights was used to characterize polyacrylamide (PAL) films spin-coated on the gold (Au) surfaces. The PAL films spin-coated on the Au surface show the characteristics of a bi-layered structure. The first layer attached to the Au surface with a thickness of around 70 nm shows no chain orientation due to the dewetting effect of the Au surface. The upper layer is composed of the PAL molecules oriented parallel to the Au surface as the film thickness increases, which is believed to be due to the spin-coating effect. The bottom and the top layers are optically isotropic and anisotropic, respectively, as confirmed by the analysis of the RA-FTIR spectra. The thickness-threshold is of the order of the end-to-end distance (R_ee, 67 nm) of PAL molecules (M_w ∼ 10⁶) indicating the dewetting distance through which the Au surface functions.