Key Engineering Materials Vol. 840

Abstract: The study of spectroscopic ellipsometry on gold thin film with different thicknesses (30, 50, and 70 nm) for biosensor application has been done. In this work, a rotating analyzer ellipsometer (RAE) has been used to characterize gold thin film and detect microalgae. The measurement was performed at different incidence angles (60°, 65°, 70°, and 75°) assuming the gold film as an isotropic material. The light absorptions of electron represented by the ellipsometer parameter (Δ) and the extinction coefficient (k) are due to the intraband transition of free electrons in the lower photon energy and interband transition of bounded electrons from 5d to 6sp in the higher photon energy. The light absorption increases with the decrease in the thickness of Au thin film. However, for the detection of microalgae, the light absorption of the electron increases with the increase in the thickness of Au thin film due to the dominant absorption by microalgae and PVA. We report that the use of Au thin film with the thickness of 70 nm provides the most sensitive detection of microalgae which is confirmed by the change in Δ (63.1°), at the photon energy of 2.11 eV and the incidence angle of 75°.

Abstract: The quartz crystal microbalance (QCM) modified by chitosan/α-pinene, prepared by spin-coating technique has been successfully developed with molecular imprinting polymer (MIP) concept. To remove the template, we carried out two treatments namely heating and vacuum in a desiccator. To find out selectivity of the sensor, the QCM modified with polymer chitosan has been tested with another analyte such as acetone, ethanol, N-amyl alcohol, iso-amyl alcohol. The result shows that chitosan/α-pinene coated QCM sensor can provide a good response as good as sensitivity. The best QCM at heating treatment in a furnace with the decline of frequency is 32 Hz, then the QCM vacuum pumping treatment with decline frequency is 27 Hz.

Abstract: Poly hydroxyethyl methacrylate (p-HEMA) has a natural property that is very easy to absorb a liquid or solution and become a hydrogel when absorbing water. In this work, by combining p-HEMA material with a cholesteric liquid crystal (CLC), the material can absorb the solution and the optical properties of the liquid crystal will change depending on the solution it absorbs. The solution used in this work is acetone. During the absorption process the p-HEMA material expanded so that the orientation direction of liquid crystal molecular twist with a helical axis along can freely move and change. In this work, we observed the study of transmittance caused by thickness effect and the mixture concentration effect of the poly hydroxyethyl methacrylate liquid crystals (PHM-LC).

Abstract: In this study, Fast Fourier Transform (FFT) was used in order to detect bore hole in a structure. FFT is a common method in digital signal processing (DSP) to characterize the frequency emitted by some structure. This method is widely used because of its simplicity. Computational time needed for FFT is relatively lower than another method. The use of FFT to analyze defect in structure is not commonly used since FFT has some weakness for example spatial frequency cannot be extracted to point out the defect location. In this paper, defect was designated as a hole in a strip iron plate with 20 mm in diameter. The strip iron plate was 1 meter long, 38 mm wide and 3 mm thick. This strip iron plate was clamped at one of its ends while the other side is left free. In order to produce vibration signal, impact hammer Bruel Kjaer Type 8202 was used with plastic tip to limit the vibration frequency in to the range of 0 - 1000 Hz. The trigger point was 30 mm from its free end. Three accelerometers were placed series in one line with the trigger point with 300 mm distance of each accelerometer. The position of the hole was varied in three different position. The first position was between trigger point and first accelerometer, between first and second accelerometer and between the second and third accelerometer. The raw signal obtained from the accelerometer was processed by using FFT to understand the mode shape changes in the strip iron plate due to the bore hole. Furthermore, the FFT result was analyzed as function of receiver position to determine the position of hole. The result shows that the frequency characters were different in each case and further analysis by using magnitude-squared coherence function need to be used in order to quantitatively find the difference between FFT result.

Abstract: This study aims to investigate the effect of SWCNT nanofiller on mechanical properties and electrical conductivity of PVA/CS/GA nanocomposite film. Polyvinyl alcohol (PVA) and chitosan (CS) are used as polymer matrix that crosslinked by glutaraldehyde (GA). Nanofiller SWCNT was inserted in a polymer composite matrix at different composition. The thin films were characterized using FTIR (Fourier Transform Infrared Spectroscopy), XRD (X-ray diffraction), SEM (Scanning Electron Microscopy), TG/DTA (Thermal Gravimetric/Differential Thermal Analysis), sheet resistance, and tensile strength measurements. The results revealed that the addition of SWCNT notably increased the electrical conductivity of composite film from 1.2 x 10^‒4 S.cm^‒1 to 9 x10^‒3 S cm^‒1 as well as tensile strength and elongation 43 MPa to 62 MPa, 68% to 84%, respectively. The cross-sectional SEM images indicated that the conductive thin films have a layered structure where the insertion of SWCNT did not change their morphological structure significantly. Additionally, SWCNT improved the thermal stability of PVA/CS/GA nanocomposites thin film. These finding can be promising for the development of optoelectronic devices i.e. photovoltaic, emitting diodes, etc.

Abstract: Dielectric properties of Zn substituted cobalt ferrite (Co_1-xZn_xFe₂O₄) magnetic nanoparticles with various Zn concentrations (x = 0.2-0.8) have been successfully investigated. The structure of the prepared samples Co_1-xZn_xFe₂O₄ confirmed to be cubic spinel structure using X-ray diffraction analysis. The crystallite size of the sample was found to decrease with the increase of zinc content from 11.6 nm to 9.8 nm, while the lattice parameters found to increase with the increase of zinc from 8.18 to 8.25 Å. For Zinc x = 0.6 at frequency 5 kHz have the highest real dielectric constant (ɛ') was 678.8 and imaginary dielectric constant (ɛ'') was 833.3. The maximum impedance found at zinc x = 0.3 was 138.5. The dielectric constant decrease rapidly with increasing the frequency and then reaches the constant value where the frequency was used from 5-120 kHz.

Abstract: TiO₂ modified Fe₃O₄ nanocomposite as photocatalyst in CO₂ indirect reduction was synthesized by an ultrasonic-assisted sol-gel method and its photocatalytic activity was studied as well. The modification of the TiO₂ composite was attempted to modify titanium dioxide to have better performance as a photocatalyst. Magnetite synthesis was carried out by the sono-coprecipitation method with the addition of the capping agent. The magnetite was coated with TiO₂ via the sol-gel method under ultrasonic irradiation. The products were characterized by X-ray diffraction (XRD), Fourier transforms infrared spectrophotometry (FT-IR), transmission electron microscopy (TEM), and turbidimetry. The final product was also analyzed by diffuse reflectance UV-Visible (DR-UV) and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX). The product of indirect reduction was analyzed by gas chromatography-mass spectrometry (GC-MS). Photocatalytic reaction with Fe₃O₄/TiO₂ nanocomposite produced a higher concentration of methanol than using TiO₂. Methanol concentration produced from the photocatalytic reaction using TiO₂ and Fe₃O₄/TiO₂ was 6.63% and 16.82%.

Abstract: The optical properties and electro-hydrodynamics (EHD) patterns of 4-methoxybenzylidene-4-butylaniline (MBBA) which is parallel oriented by nanofibers has been observed. The alignment of the liquid crystals was made using polyvinyl alcohol (PVA) nanofiber by used modified electrospinning. Electrospinning method was modified using two commercial copper (Cu) printed circuit board (PCB) as a gap collector. These planar samples area is 20 mm x 25 mm. The optical characteristic of these samples was studied by using an optical polarizing microscope. The optical intensity changes by a rotation of crossed polarizers are observed. When an electric field was applied to these samples, the electrohydrodynamic (EHD) pattern was observed. At the low till high frequency, by increasing the voltage, the patterns were formed such as Williams domain (WD), fluctuating Williams domain (FWD), grid patterns (GP) and dynamic scattering Mode (DSM).

Abstract: Magnetic nanomaterials are studied extensively because of their wide range of possible applications. Synthesis of Fe₃O₄ with citrate and polyethylene glycol (PEG) as stabilizing agents was carried out. In this study, the effect of media of water, sodium citrate and polyethylene glycol as stabilizing agents on the shape and size of Fe₃O₄ magnetite nanoparticles was investigated. The synthesis of Fe₃O₄, Fe₃O₄/citrate, and Fe₃O₄/PEG was carried out by the coprecipitation method at controlled pH. The products were characterized by infrared spectrophotometry, X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy-Energy Dispersive X-Ray (SEM-EDX). Qualitative test of magnetism was also carried out on the three materials. The results showed that Fe₃O₄ nanoparticles prepared with sodium citrate and PEG have a diameter of 12 and 10 nm, respectively. In the sodium citrate medium, it gives Fe₃O₄ colloidal nanoparticle with electrostatic stabilization mode, while in the PEG medium it shows steric stabilization mode. Magnetite produced in PEG medium has the homogeneous size and is much more stable than that obtained in citrate medium

Abstract: The synthesis of gold nanoparticles (AuNPs) was carried out by reacting chloroauric acid [AuCl₄]^‒ and glutamic acid solution in a water bath at 80 °C. The reaction was confirmed by the color change from colorless solution into pink. Various concentrations of the glutamic acid solution, reaction times and pH were examined to determine the optimum condition of AuNPs synthesis. The AuNPs colloid was characterized by UV-Visible spectrophotometer at wavelength 350-800 nm, particle size analyzer (PSA) and transmission electron microscope (TEM). The optimum synthesis condition for obtained [AuCl₄]^‒ was 4 mM glutamic acid solution at pH 11 and 60 min reaction. TEM results showed that the particles were round in shape with the article size indicated by PSA was 40 nm.