Wasapinyokul, Kamol

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

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    Item type:Publication,
    Size-dependent and spatial variations in the structural properties of spin-coated poly(Vinylidene Fluoride) films
    (2025-10-01)
    Sukjit, Peemases
    ;
    Munpiriyakul, Pimpaporn
    ;
    Tuantranont, Adisorn
    ;
    Lomas, Tanom
    ;
    Borthai, Pawantree
    The uniformity of structural properties in large spin-coated poly(vinylidene fluoride), or PVDF, films is crucial due to their widespread applications and thus requires careful investigations. In this study, variations in structural properties across PVDF films of different sizes and positions were examined. Thin PVDF films were fabricated by the spin-coating method onto rectangular substrates with lengths varying from 10 mm to 40 mm while maintaining a constant width of 10 mm. Three key characteristics – thickness, phase, and crystallinity – were characterized and analyzed. Two effects were investigated – the size-dependent effects, i.e., the property variations at a specific position due to the increasing film length, and the spatial effects, i.e., the property variations along distances from the film center within a film of a specific size. The average thickness of the fabricated film was in the range of 5.00 μm to 6.00 μm, while the crystalline size was in the range of 1.00 nm to 3.00 nm. For the size-dependent effects, at a specific position on the film, increasing the film length did not significantly affect the thickness; however, the phase of PVDF shifted toward a more chain-like β phase, while the crystalline size decreased. At the film center, the crystalline size decreased by 60.7% when the film size increased from the smallest to the largest. These changes resulted from four combined mechanisms: centripetal force, viscosity, evaporation rate, and shear force. For the spatial effects, in a film with a specific size, when the distance from the center increased, the thickness decreased, the phase remained β, and the crystalline size was smaller. For the largest 40 × 10 mm<sup>2</sup> film, the thickness and crystalline size decreased by 16.7% and 3.6%, respectively, from the center to the edge of the film. These trends were attributed to the three combined mechanisms: centripetal force, viscosity, and evaporation rate. The findings of this study provide critical insights into a deeper understanding of property variations in spin-coated PVDF films among both different film sizes and different positions on a film, which is essential for optimizing their applications.
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    Item type:Publication,
    Optical transmittances of spin-coated polymer films with different spin step protocols
    (2019-07-01)
    Sukjit, Peemases
    ;
    Jaieau, Chatchai
    ;
    Wasapinyokul, Kamol
    In this report, we studied the effects of different spin-coating step protocol on the optical transmittance of thin film polymer. Thin films of poly(methylmethacrylate), or PMMA, were spin-coated with two different spin step protocols - the speed-up and speed-down protocols. In each protocol, the spin-coating had two steps, the first and the second steps. In the speed-up protocol, the first step was slow, while the second faster step was faster. In the speed-down protocol, the first step was fast, while the second step was slower. All the films were subsequently characterised for their optical transmittance over the visible region. There were at least three points worth explained from the experimental results. Firstly, for the speedup protocol, when the second-step speed was slower than 4000 rpm, the transmittance of the film were varied and did not show any relation with the first-step speed. However, when the second-step speed was faster, all the films, regardless of the first-step speed, provided roughly equal transmittance. Secondly, for the speed-down protocol, when the second-step speed was slower than 3000 rpm, transmittances from all films were varied. But when the second-step speed was faster, all the films from all first-step speed gave roughly equal transmittance. As the transmittance is related to the film thickness, these results indicated that, regardless of what the protocol was, if the second-step speed was fast, the film thickness from any first-step speeds would be roughly equal to each other. Finally, for the same pair of speeds but with different protocols, a film with a speed-down protocol provided a relatively higher transmittance than one from a speed-up protocol, implying a thinner film. The results from this study could be further developed to understand how the spin-speed protocol could be chosen to provide a thin film with required thickness.