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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    Electrolytic exfoliation of few-layer graphene/sodium dodecylbenzenesulfonate for coin- and cylindrical-cell supercapacitor electrodes
    (2023-06-01)
    Lomas, Tanom
    ;
    Poochai, Chatwarin
    ;
    Sukjit, Peemases
    ;
    Wasapinyokul, Kamol
    ;
    Mensing, Johannes P.
    Electrolytic exfoliation of graphite is a promising way to produce graphene quickly, inexpensively, and in an environmentally friendly manner. In this research, sodium dodecylbenzenesulfonate (SDBS), a commonly used anionic surfactant, was dissolved in 1 M H<inf>2</inf>SO<inf>4</inf> to produce SDBS-graphene via electrolytic graphite exfoliation. The AFM analysis validated the thickness of few-layer of SDBS-graphene between 5 and 15 nm. Then, a symmetric coin-cell (CR2032) supercapacitor (SC) comprised of SDBS-graphene and rGO (synthesized via Hummer's method) was assembled with 0.5 M H<inf>2</inf>SO<inf>4</inf> as an electrolyte. The highly exfoliated SDBS-graphene demonstrated a greater capacitive electrochemical response than rGO. The CV and GCD techniques revealed that the specific capacitance of SDBS-graphene was 150 F g<sup>−1</sup> at 0.25 A g<sup>−1</sup> with 20.4 Wh kg<sup>−1</sup> of energy density and 494 W kg<sup>−1</sup> of power density and that its percentage capacitive retention remained 95 % after 10,000 cycles at 3 A g<sup>−1</sup>, compared to the specific capacitance of reduced graphene. In addition, a cylindrical cell SC (CR32650) with SDBS-graphene demonstrated a capacitance of 220 F at 100 mA, along with an energy density of 33 kWh and a power density of 55 kW. This suggests that exfoliated SDBS-graphene may be utilized in SCs with high efficiency and long-term durability.