Wasapinyokul, Kamol

Preferred name

Wasapinyokul, Kamol

Main Affiliation

Integrated Innovative Technology

kamol.wa@kmitl.ac.th

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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
;
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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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 2<sup>nd</sup>-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 2<sup>nd</sup>-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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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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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.
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Optical transmittances of spin-coated polymer films with different spin step protocols
(2019-07-01)
Sukjit, Peemases
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Jaieau, Chatchai
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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.
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A study of optical properties of thin film polymer spin-coated with different dispensing methods
(2019-07-01)
Phatcharawutikul, Ronakrit
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Tangtrakul, Kitbordee
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Wasapinyokul, Kamol
Thin films of poly(methyl methacrylate), PMMA, were fabricated by using a spin-coating process with two different dispensing methods: static and dynamic ones. In the former and latter methods, the solution was dropped onto the substrate when the substrate was stationary and spinning, respectively. The films were characterised for their optical transmittance. The results show that the films from the dynamic dispensing method would provide higher optical transmittances than those from the static ones, indicating the thinner films. This could be explained as, in the dynamic method, the film would always be in a dynamic state and therefore could not form the film easily, resulting in a thinner film. Another point worth noting is that, in the dynamic method, the dispensing height affected the film's transmittance. The higher the dispensing height, the higher the transmittance. This indicated a thinner film and could be explained that, in the dynamic method, a higher dispensing height would result in a larger proportion of the liquid drop to bounce off the substrate, hence less amount of liquid remained to form the film, leading to a thinner film. Such characteristic did not appear in the static method because in this method, the liquid was dropped carefully and covered all the substrate before the spinning started. The results from this study could help choosing the dispensing method to provide film with required optical properties.
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Effects of spin-coating recipe on the transmittance of spin-coated TiO2 films
(2018-09-05)
Ponkasemsuk, Worathat
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Panjasamanwong, Tanakrit
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Nudee, Thitiwat
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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.

Wasapinyokul, Kamol

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