Flexible polymer opal films prepared by slide coating from alcoholic media

In this study, we investigated the fabrication of a colloidal photonic crystal film on flexible substrate, which can be used as a scaffold material for various photonic applications. A thin polyethylene terephthalate (PET) film was treated by oxygen plasma and then used as a flexible substrate. The surface characterizations revealed that the surface roughness increased, and that the treated PET film was rendered hydrophilic. The contact angles of the films with water/isopropyl alcohol (IPA) mixtures at five different weight ratios (25%, 40%, 50%, 60%, and 75% of IPA) prepared on both treated and non-treated PET films were measured. The results indicated that water/IPA wets on oxygen plasma-treated PET film. The colloidal dispersions were prepared in five different water/IPA mixtures, and slide coating was carried out on both PET films aided by hot air to promote opal formation. Serious dewetting of opal film was observed on the non-treated PET film, except that with a 75% IPA. However, the treated PET film enabled the formation of high-quality opal film, regardless of IPA content in colloidal dispersion. The optical properties and surface morphologies of opal films on flexible PET film were confirmed by reflectance spectra and scanning electron microscopy images of the respective films.