Wasapinyokul, Kamol

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Wasapinyokul, Kamol
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kamol.wa@kmitl.ac.th

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    Item type:Publication,
    Mathematical model for thickness of off-center spin-coated polymer films
    (2020-02-10)
    Wasapinyokul, Kamol
    ;
    Panjasamanwong, Tanakrit
    ;
    Ponkasemsuk, Worathat
    ;
    Sriprachuabwong, Chakrit
    ;
    Lomas, Tanom
    Off-center spin coating is a method to fabricate thin film on a substrate where the substrate is located at an off-center distance away from the rotating center of the spin coater. Here, a mathematical model to calculate the thickness of a film fabricated by an off-center spin-coating technique was developed and proposed. The model showed that the off-center film thickness was calculable by using four factors—the on-center film thickness, mass fraction of solid in the wet film, length of the substrate in the radial direction, and off-center distance. Simply, the off-center film thickness was inversely proportional to the off-center distance to the exponent of one-third, that is, the further the off-center distance, the thinner the film. The model was verified where the thicknesses of the films calculated by using the model were compared with the experimental values obtained from the off-center spin-coated films of poly(vinylidene fluoride) at various off-center distances. Both the modeled and the experimental data were of the same trend and in a good agreement with each other, indicating the validity of the model. The limitations of the model were also discussed. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48356.
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    Effects of spin-coating recipe on the transmittance of spin-coated TiO2 films
    (2018-09-05)
    Ponkasemsuk, Worathat
    ;
    Panjasamanwong, Tanakrit
    ;
    Nudee, Thitiwat
    ;
    Wasapinyokul, Kamol
    Effects of the stirring time in TiO<inf>2</inf> sol chemical on the optical transmittance of the spin-coated films over the visible-to-near-infrared region were studied. It was observed that the longer stirring time, from 12 hours to 48 hours could provide films with either observably higher or lower transmittance, depending on the solvent. In Isopropanol, or IPA, the longer stirring time of the sol chemical leaded to a lower optical transmittance. In hydrochloric acid, or HCl, the trend was reversed; the longer stirring time of the sol chemical would cause a higher optical transmittance. Effects in both solvent were more pronounced at lower wavelengths, i.e. the increasing or decreasing of the transmittance with the extended stirring time could be seen more noticeably at low wavelengths. We believed that these phenomena were caused by the change in dispersion of the TiO<inf>2</inf> particle in the solvent over the stirring time. In HCl, which is an acid-based solvent, the particle could be better dispersed than that in IPA, resulting in a proportional relation between the stirring time and the transmittance of the spin-coated films. This assumption was supported when the transmittance of the films in IPA and HCL were compared as it could be seen that the transmittance of the former was lower. The results from this study could be used to help select an appropriate preparation time of the TiO<inf>2</inf> sol chemicals in different solvents to obtain a spin-coated film with a required level of optical transmittance.