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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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Non-monotonic evolution of the responses of ZnO-nanoparticle UV-sensitive devices under ambient aging
(2023-08-01)
Sratongkham, Pittayathorn
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Chuenchom, Rattana
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Tuantranont, Adisorn
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Lomas, Tanom
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Wasapinyokul, Kamol
Ultraviolet (UV) sensitive devices based on spin-coated zinc-oxide nanoparticles (ZnO) were fabricated and characterised. They were subsequently stored in the ambient and dark conditions with low humidity for 56 days, during which time they were intermittently recharacterised to determine the aging effect on their sensing properties, including responsivity, sensitivity, and response and recovery times. Over the 56-day period, both the dark and illumination currents increased, causing the non-monotonic evolution of the performances of the devices – the responsivity improved by 9–18 folds, the sensitivity remained stable, and the response and recovery times deteriorated as they were 46 and 33 times longer, respectively. These changes were associated with an increase in the number of adsorbed oxygen molecules on the ZnO surface with time. This resulted in more photodesorbed oxygen molecules and thus more remaining charge carriers under illumination, which increased the photo-generated current and consequently responsivity. However, it also caused the current to rise and decay more slowly when the illumination appeared and disappeared, respectively, leading to the prolonged response and recovery times. The longer recovery times led in an increase in dark current, which, when combined with an increase in illumination current, resulted in a stable sensitivity. The trends of these sensing parameters were similar, but to varying degrees, regardless of the change in the radiation levels and ZnO layer thicknesses.
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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
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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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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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A Screen Printed Graphene Based Electrochemical Sensor for Single Drop Analysis of Hydroquinone in Cosmetic Products
(2019-08-01)
Duekhuntod, Wannida
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Karuwan, Chanpen
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Tuantranont, Adisorn
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Nacapricha, Duangjai
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Teerasong, Saowapak
A graphene modified carbon paste sensor (or so-called graphene based sensor) was developed for electrochemical detection of hydroquinone. The sensor was fast fabricated using screen-printing technique. By integrating three fundamental electrodes on a single device, the sensor is small and portable. A determination is based on a one drop analysis. A 60 μ.L-drop of sample was placed onto the sensor prior to cyclic voltammetric measurement. The method relies on green analysis since it lowers the consumption of sample and waste generation. Under the optimal conditions, a linear calibration was achieved in range of 1.0 x 10-4 to 5.0 x 10-3 M hydroquinone. The detection limit was 7 x 10-5 M, a sensitive adequate for measuring hydroquinone in cosmetic products. The sensor provided good precision (%RSD = 2.78) and accuracy (recoveries = 87-114%), with analysis times of less than a minute. The sensor was applied to determine the presence of hydroquinone in whitening creams. The results obtained from the developed sensor satisfactorily agreed with the HPLC method, indicating the reliability of the method. Due to its advantages in terms of rapidity, low-cost and portability, the device is a viable choice for on-site screening for hydroquinone contamination in whitening products.
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Real-time multianalyte biosensors based on interference-free multichannel monolithic quartz crystal microbalance
(2015-05-05)
Jaruwongrungsee, Kata
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Waiwijit, Uraiwan
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Wisitsoraat, Anurat
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Sangworasil, Manas
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Pintavirooj, Chuchart
In this work, we design, fabricate and characterize a new interference-free multichannel monolithic quartz crystal microbalance (MQCM) platform for bio-sensing applications. Firstly, interference due to thickness-shear vibration mode coupling between channels in MQCM array is effectively suppressed by interposing a polydimethylsiloxane wall between adjacent QCM electrodes on a quartz substrate to form inverted-mesa-like structure. In addition, the electrical coupling due to the electrical impedance of solution is diminished by extending the flow path between them with an extended-design flow channel. The electrical testing results show that individual QCM signal is unaffected by those of adjacent channels under liquid loading, signifying the achievement of interference-free MQCM. The MQCM is applied for multi-analyte biosensing of IgG and HSA. The anti-IgG and anti-HSA are separately immobilized on two adjacent QCM electrodes, which are subsequently blocked with BSA to avoid unspecific binding. The MQCM biosensors are tested with single- and double-analyte solutions under continuous flow of buffer. The IgG and HSA QCM sensors only show frequency shift responses to their corresponding analytes and there are very small cross frequency shifts due to remnant unspecific binding. Moreover, MQCM sensors show approximately linear frequency shift response with analyte concentration. Therefore, the developed MQCM platform is promising for real-time interference-free label-free detection and quantification of multiple bio-analytes.
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Metamaterial-based microfluidic sensor for dielectric characterization
(2013-01-01)
Withayachumnankul, Withawat
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Jaruwongrungsee, Kata
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Tuantranont, Adisorn
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Fumeaux, Christophe
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Abbott, Derek
A microfluidic sensor is implemented from a single split-ring resonator (SRR), a fundamental building block of electromagnetic metamaterials. At resonance, an SRR establishes an intense electric field confined within a deeply subwavelength region. Liquid flowing in a micro-channel laid on this region can alter the local field distribution and hence affect the SRR resonance behavior. Specifically, the resonance frequency and bandwidth are influenced by the complex dielectric permittivity of the liquid sample. The empirical relation between the sensor resonance and the sample permittivity can be established, and from this relation, the complex permittivity of liquid samples can be estimated. The technique is capable of sensing liquid flowing in the channel with a cross-sectional area as small as (0.001λ<inf>0</inf>)2, where λ<inf>0</inf> denotes the free-space wavelength of the wave excitation. This work motivates the use of SRR-based microfluidic sensors for identification, classification, and characterization of chemical and biochemical analytes. © 2012 Elsevier B.V.
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Metamaterial-inspired microfluidic-based sensor for chemical discrimination
(2012-12-01)
Jaruwongrungsee, Kata
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Withayachumnankul, Withawat
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Wisitsoraat, Anurat
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Abbott, Derek
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Fumeaux, Christophe
This work proposes a metamaterial-inspired microfluidic-based chemical sensor. The sensor comprises a microwave split-ring resonator (SRR), an important building block of metamaterials, integrated with a disposable flow-channel made of a transparency film. The electromagnetic response of the sensor is observed in the presence of various analytes including glycerol, ethanol, and phosphate buffered saline. It is found that the resonance frequency in the transmission amplitude and the zero crossing in the reflection phase of the sensor are good features for discrimination of these analytes and for determining their concentrations. The developed metamaterial-inspired microfluidic-based chemical sensor has a potential for advanced chemical sensing applications. © 2012 IEEE.
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The preliminary study of lactate detection based on lactate dehydrogenase/nictotinamide adenine dinucleotide
(2012-12-01)
Taertulakarn, Somchat
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Tobanluepop, Pussadee
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Tuantranont, Adisorn
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Pintavirooj, Chuchart
This study reports the preliminary development to biosensor using electrochemistry for lactate analysis. In this work, PEDOT/PSS modified screen printed carbon was developed as working electrode with lactate dehydrogenase (LDH), the oxidized form of nicotinamide adenine dinucleotide (NAD+) and glutaraldehyde. The result shows that the current from working electrode with PEDOT/PSS were higher compared with screen printed carbon electrode. These results were consistent with PEDOT/PSS properties that are conducting polymers and can help for more rapid electron transfer. These favorable characteristics allowed its application to detect normal blood lactate concentration in human beings. ©2012 IEEE.
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Synthesis of carbon nanotube and carbon nanofiber in nanopore of anodic aluminum oxide template by chemical vapor deposition at atmospheric pressure
(2012-10-15)
Kasi, Jafar Khan
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Kasi, Ajab Khan
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Wongwiriyapan, Winadda
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Afzulpurkar, Nitin
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Dulyaseree, Paweena
Carbon nanotube (CNT) is one of the most attractive materials for the potential applications of nanotechnology due to its excellent mechanical, thermal, electrical and optical properties. We demonstrated the fabrication of carbon nanotube and carbon nanofiber (CNF) inside the pore and at the surface of anodic aluminum oxide (AAO) membrane by chemical vapor deposition method at atmospheric pressure. Ethanol was used as a hydrocarbon source and Co-Mo as catalyst. CNT was synthesized at different temperature. High graphitic multiwall carbon nanotube (MWCNT) was found at 750°C, while CNF was found at 800oC and above temperature analyzing by Raman spectroscopy. © (2012) Trans Tech Publications, switzerland.

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