Wasapinyokul, Kamol

Preferred name

Wasapinyokul, Kamol

Main Affiliation

Integrated Innovative Technology

kamol.wa@kmitl.ac.th

Now showing 1 - 10 of 16

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Highly-transparent multi-layered spin-coated silk fibroin film
(2017-01-01)
Wasapinyokul, Kamol
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Kaewpirom, Supranee
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Chuwongin, Santhad
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Boonsang, Siridech
In this study, the silk fibroin films with different numbers of layers were fabricated by the spin-coating method and their optical transmittances were observed. The process to synthesise the silk fibroin solution was explained - starting from the silk cocoon until the silk-fibroin solution, approximately 7.5% concentration wt/vol, was obtained. The solution was spin-coated onto clean glass substrates to fabricate samples. Totally 10 samples with different numbers of layers, from 1 to 5 layers, were obtained. All samples can be separated into two groups: those left dried at room temperature after spin-coating and those heated at 60°C. They were then measured for their transmittance over the visible-to-near-infrared region. All samples exhibited the high transmittance where the values were at 95% and 98%, for the samples at room temperature and those at 60°C, respectively. This was believed to be due to the heating effect that caused the silk fibroin to arrange itself after being heated, hence the higher transmittance. These high transmittances were maintained regardless of the number of layers and length of heating time. Results from this study could be used to fabricate a silk fibroin film with high optical transmittance and adjustable other properties.
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Accuracy of swanepoel method in calculation of polymer film thicknesses
(2021-08-01)
Kesornkhup, Sarunrit
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Tuantranont, Adisorn
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Lomas, Tanom
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Sriprachuabwong, Chakrit
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Wasapinyokul, Kamol
We studied the accuracy of the Swanepoel method in the calculation of thicknesses of spin-coated poly(methyl methacrylate) films with thicknesses up to 2500 nm. Their thicknesses were calculated by using the Swanepoel method and subsequently compared with the measured actual values. Results showed that both thicknesses followed identical trends where films with higher solution concentrations or slower spin-coating speeds were thicker. The relative difference between the Swanepoel and the actual thicknesses was explained through the thickness of the flat region where the interference of transmitted light occurred. For a film whose flat region was thinner or thicker than other features of the film, its Swanepoel thickness was lower or higher, respectively, than the actual average value. Errors of the Swanepoel thicknesses from the actual values were analysed to find their correlation with the film surface roughness and thickness. When the film roughness and thickness increased fivefold, the error increased threefold and 1.6 times, respectively, indicating that the effect of the film roughness was predominant. Mathematically, this effect was the result of the fact that when roughness increased, the interference pattern shrank, and hence the values deviated. For the effect of thickness, thicker films had higher roughness, and consequently higher errors. Errors of as low as 5% and 0.86% were observed for films with the roughness of less than 15 nm and those with the thickness of 1800 nm, respectively. This showed that the method can be used to calculate the thickness of μm-thick polymer films, with a good level of roughness, with satisfying accuracy.
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Transmittance of baked spin-coated poly(methyl methacrylate) films
(2018-09-05)
Jaipean, Assanee
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Suriyakiat, Phasit
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Wasapinyokul, Kamol
Thin films of poly (methyl methacrylate), or PMMA, were fabricated by a spin-coating method and the effects of two fabrication recipes - the 2nd-step spin-coating speed and the baking temperature after spin-coating - on the optical transmittance of the film over the visible-to-infrared region were examined. For the 2nd-step spin-coating speed, it was observed that the transmittance of the film increased with the speed, but with a decreasing rate. This could be attributed to the film thickness; the film with a faster coating speed would be thinner, leading to higher transmittance. For the baking temperature, all the baked films provided roughly the same level of transmittance regardless of their baking temperatures after spin-coating, except the one baked at 130 °C. The sample baked at such temperature provided approximately 5% lower transmittance than those of the others. This effect was supposedly contributed to the glass transition temperature of the PMMA. The baking temperature of 130°C was closed to the glass transition temperature of the material which is at 105°C. Thus the film baked at such temperature was supposedly in a mixture of glassy state and solid state, leading to a disordered morphology and hence lower transmittance. The results from this study could be used to help adjust the fabricating conditions of a spin-coated film of PMMA to provide a required optical transmittance.
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Mathematical model for thickness of off-center spin-coated polymer films
(2020-02-10)
Wasapinyokul, Kamol
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Panjasamanwong, Tanakrit
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Ponkasemsuk, Worathat
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Sriprachuabwong, Chakrit
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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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Modification of optical properties of spin-coated TiO2 film by heat treatments
(2017-01-01)
Chunarom, Chutinat
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Yontrarak, Tanapat
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Wipopcharoenkul, Puttinan
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Wasapinyokul, Kamol
In this report, effects of heat treatment conditions on the transmittance of titanium dioxide, TiO<inf>2</inf>, films were examined. The colloidal solution of TiO<inf>2</inf> in two different solvents - isopropanol, IPA, and sulfuric acid, H<inf>2</inf>SO<inf>4</inf>, were deposited via a spin-coating method onto clean glass substrates. The films were subsequently annealed and cooled down, either quickly or slowly, before being measured for their optical transmittances in the visible region. Three points were noted: Firstly, when the films were quickly cooled down after annealed, their transmittance depended on their annealing temperature. In IPA and H<inf>2</inf>SO<inf>4</inf>, the transmittance decreased and increased, respectively, when the annealing temperature increased. Secondly, when the films were slowly cooled down after annealed, their transmittance seemed to be independent from the annealing temperature, where the films had roughly equal transmittance regardless of annealing temperature. Lastly, the TiO<inf>2</inf> films with H<inf>2</inf>SO<inf>4</inf> provided higher transmittance than those with IPA. All the three stated characteristics were the same for all wavelengths in the visible region. These results were believed to result from the dispersibility of the TiO<inf>2</inf> in each solvent and the cooling-down processes. Such results could be further developed to select a suitable heat treatment process for a spin-coated TiO<inf>2</inf> film with a desired optical transmittance.
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Predictive Three-Dimensional CFD Modeling of Evaporation-Coupled PVDF/DMF Spin-Coating on Finite Square Substrates
(2026-01-01)
Vichachai, Ratiwat
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Thongsri, Jatuporn
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Wasapinyokul, Kamol
Predictive thickness control remains challenging for spin-coated polymer films on finite, noncircular substrates, particularly with solvent evaporation. This study presents a three-dimensional computational fluid dynamics framework to simulate poly(vinylidene fluoride) dissolved in dimethylformamide during spin-coating on a finite square substrate. The model resolved free-surface hydrodynamics, interfacial solvent evaporation, species transport, and concentration-dependent viscosity to capture evaporation-coupled thinning dynamics. The simulation results were corrected with a dry-film equation based on mass conservation to obtain the film profiles. Two simulated cases—nonevaporating and evaporating—were investigated for three parameters—spin-coating time, rotational speed, and solution concentration. The nonevaporating model was validated against the one-dimensional analytical solution, while the evaporating model was validated against experimental values. Both the simulated and experimental thicknesses exhibited good quantitative agreement, confirming that the model accurately captured the film formation mechanisms. Remaining discrepancies were attributed to liquid retention at the substrate edge, uncertainty in initial dispensed volume, and numerical resolution effects near the interfacial regions. The model revealed that evaporation-induced viscosity evolution significantly modified thinning behavior, particularly at low speeds and high concentrations, and amplified edge accumulation on finite substrates. This work establishes a predictive framework for thickness and profile control in spin-coated polymer films.
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Size-dependent and spatial variations in the structural properties of spin-coated poly(Vinylidene Fluoride) films
(2025-10-01)
Sukjit, Peemases
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Munpiriyakul, Pimpaporn
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Tuantranont, Adisorn
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Lomas, Tanom
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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 mm2 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
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Poochai, Chatwarin
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Sukjit, Peemases
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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−1 at 0.25 A g−1 with 20.4 Wh kg−1 of energy density and 494 W kg−1 of power density and that its percentage capacitive retention remained 95 % after 10,000 cycles at 3 A g−1, 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.
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Impressive Response of Spin-Coated ZnO Nanoparticle UV-Sensitive Devices with Various Thicknesses under Different UV Intensities
(2021-09-01)
Pawong, Whongsatorn
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Wasapinyokul, Kamol
We fabricated ultraviolet (UV) detectors based on spin-coated pure zinc oxide (ZnO) nanoparticles with a metal–semiconductor–metal configuration. Devices with various ZnO layer thicknesses were characterized under different UV intensities, and their responsivity, sensitivity, response time, and recovery time analyzed. The following performance was achieved: responsivity of 99.8 A W−1, sensitivity of 531.1, and response and recovery times of 0.01 s and 0.07 s, respectively. Increasing the thickness revealed monotonic effects on each property: the responsivity decreased, the sensitivity decreased, and the response and recovery times increased, mainly because of the thin penetration depth of ZnO and the lengthened cracks on the thicker layer. However, the effects of the UV intensity on the parameters were not monotonic. Indeed, as the intensity was increased, the responsivity decreased, the sensitivity first increased then decreased, the response time first increased before shortening, while the recovery time consistently shortened. Such trends resulted from the combination of several mechanisms: shrinkage of depletion layers, saturation of excitons, and saturation of trapping states. Increasing the radiation-on time shortened both the response and recovery times. This device performance is impressive compared with devices with more complicated material formats, device structure, or fabrication methods. Some complications in the work are also discussed.
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Effects of quenching process on the optical properties of thin film polymers
(2019-07-01)
Jumpar-Ngern, Jitrin
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Sompong, Khanisorn
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Wasapinyokul, Kamol
Polymer is a group of materials applied in several thin film electronic devices. A typical fabrication process of the material consists of coating it as a film onto a substrate by a wet process, followed by the baking and annealing the film to change its molecular structures, and hence its properties. In this study, we reported the effect of the quenching process, or the cooling down process after baking, on the optical transmittance of the film. Thin films of poly(methyl methacrylate), or PMMA, was coated on a substrate and then baked at different temperatures followed by either a quick or slow cool-down quenching process; before they were checked for their optical transmittances. The results showed that the film baked at a temperature slightly higher than the glass transition temperature of the polymer, followed by a slow cool-down quenching process would provide the transmittance apparently lower than those of the films baking and quenching at other conditions. We believe that this was because when the polymer was baked above such temperature, the polymer was in its glassy state. When it was slowly cooled down, the molecules had time to form crystalline structure, hence a lower optical transmittance. The result from this study indicated that the quenching process can be used to control the properties of a polymer film and hence should be carefully practiced.

Wasapinyokul, Kamol

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