W. Mahmood Mat Yunus

Effect of particle size on nonlinear refractive index of Au nanoparticle in PVA solution

Nonlinear refractive index of Au nanoparticle suspended in PVA solution was measured using a single beam Z-scan technique. Measurements were carried out using a green CW laser beam operated at 532 nm as excitation source. Five nanoparticle samples with different particle sizes were prepa red by γ radiation method. The Au nano-fluid shows a good third order nonlinear response for particle sizes ranging from 7.0 nm to 18.7 nm. The sign of the nonlinear refractive index was found to be negative and the magnitude was in the order of 10-8 cm2/W. The results show that the nonlinear effect tends to be increased linearly with the increasing of particle sizes thus could be a good candidate for nonlinear optical devices.

Surface plasmon resonance spectroscopy as an alternative for sensing heavy metal ions: a review

Purpose – The purpose of this paper is to review the novel application of surface plasmon resonance (SPR) in sensing heavy metal ions and the development of SPR to become an alternative heavy metal ions sensor. Design/methodology/approach – The possible dangerous toxic effects of heavy metal ions are revealed in the short introduction. The existing conventional methods for sensing heavy metal ions and their drawbacks are also discussed. To overcome these drawbacks, SPR has been investigated from the basic principle to the potential alternative in sensing heavy metal ions. Findings – Application of SPR in sensing heavy metal ions emerged a decade ago. A wide range of active layers or recognition elements (e.g. polymer, protein, nanoparticles) have been developed to combine with SPR. The detection limit, sensitivity and selectivity of SPR sensing in heavy metal ions have been improved from time to time, until the present. Originality/value – This paper provides up-to-date and systematic information on SPR s...

Physical properties of normal grade biodiesel and winter grade biodiesel.

In this study, optical and thermal properties of normal grade and winter grade palm oil biodiesel were investigated. Surface Plasmon Resonance and Photopyroelectric technique were used to evaluate the samples. The dispersion curve and thermal diffusivity were obtained. Consequently, the variation of refractive index, as a function of wavelength in normal grade biodiesel is faster than winter grade palm oil biodiesel, and the thermal diffusivity of winter grade biodiesel is higher than the thermal diffusivity of normal grade biodiesel. This is attributed to the higher palmitic acid C16:0 content in normal grade than in winter grade palm oil biodiesel.

The effect of volume fraction concentration on the thermal conductivity and thermal diffusivity of nanofluids: Numerical and experimental

This article reports on the effect of aluminum (Al) volume fraction concentration on the thermal conductivity and thermal diffusivity of Al nanoparticles suspended in water, ethylene glycol, and ethanol based fluids prepared by the one step method. The Al nanoparticles were independently produced and then mixed with a base fluid to produce the nanoparticles suspension. The thermal conductivity and thermal diffusivity of the nanofluids were measured using the hot wire-laser beam displacement technique. The thermal conductivity and thermal diffusivity were obtained by fitting the experimental data to the numerical data simulated for Al in distilled water, ethylene glycol, and ethanol. The thermal conductivity and thermal diffusivity of the nanofluids increase with an increase in the volume fraction concentration.

Synthesis of Silver Nanoparticles Dispersed in Various Aqueous Media Using Laser Ablation

The particle size, morphology, and stability of Ag-NPs were investigated in the present study. A Q-Switched Nd: YAG pulsed laser (λ = 532 nm, 360 mJ/pulse) was used for ablation of a pure Ag plate for 30 min to prepare Ag-NPs in the organic compound such as ethylene glycol (EG) and biopolymer such as chitosan. The media (EG, chitosan) permitted the making of NPs with well dispersed and average size of Ag-NPs in EG is about 22 nm and in chitosan is about 10 nm in spherical form. Particle size, morphology, and stability of NPs were compared with distilled water as a reference. The stability of the samples was studied by measuring UV-visible absorption spectra of samples after one month. The result indicated that the formation efficiency of NPs in chitosan was higher than other media and NPs in chitosan solution were more stable than other media during one month storage. This method for synthesis of silver NPs could be as a green method due to its environmentally friendly nature.

Study of the Effect of Volume Fraction Concentration and Particle Materials on Thermal Conductivity and Thermal Diffusivity of Nanofluids

Nanofluids, a mixture of nanoparticles and fluids, have exceptional potential to improve their effective thermal conductivity and thermal diffusivity, aluminum and aluminum oxide nanofluids with five different volume fractions of nanoparticle suspensions in different base fluids, i.e., distilled water, ethylene glycol (EG), and ethanol were prepared by mixing nanopowder and base fluids. Sonication with high-powered pulses was used to ensure the dispersion of nanoparticles in good uniformity in the base fluids. The hot wire-laser beam displacement technique was used to measure thermal conductivity and thermal diffusivity of the prepared nanofluids. The effects of the volume fraction concentration and particle materials on the thermal conductivity and thermal diffusivity of nanofluids were determined. The results showed that the thermal conductivity and thermal diffusivity increased linearly with increasing volume fraction concentration of nanoparticles in the respective base fluids. In addition, the thermal conductivity and thermal diffusivity increased faster in the Al2O3 nanofluids than in all the three base fluids.

Development of surface plasmon resonance sensor for determining zinc ion using novel active nanolayers as probe.

In this study, novel active nanolayers in combination with surface plasmon resonance (SPR) system for zinc ion (Zn(2+)) detection has been developed. The gold surface used for the SPR system was modified with the novel developed active nanolayers, i.e. chitosan and chitosan-tetrabutyl thiuram disulfide (chitosan-TBTDS). Both chitosan and chitosan-TBTDS active layers were fabricated on the gold surface by spin coating technique. The system was used to monitor SPR signal for Zn(2+) in aqueous media with and without sensitivity enhancement by TBTDS. For both active nanolayers, the shift of resonance angle is directly proportional to the concentration of Zn(2+) in aqueous media. The higher shift of resonance angle was obtained for chitosan-TBTDS active nanolayer due to a specific binding of TBTDS with Zn(2+). The chitosan-TBTDS active nanolayer enhanced the sensitivity of detection down to 0.1 mg/l and also induced a selective detection towards Zn(2+).

Synthesis and Physical Characterization of Carbon Nanotubes Coated by Conducting Polypyrrole

This study describes the preparation of polypyrrole multiwall carbon nanotube (PPy/MWNT) composites by in situ chemical oxidative polymerization. Various ratios of functionalized MWNTs are dispersed in the water, and PPy are then synthesized via in-situ chemical oxidative polymerization on the surface of the carbon nanotubes. The morphology of the resulting complex nanotubes (MWNT-PPY) was characterized by field-emission scanning electron microscopy (FESEM). The conductivity of each composite showed a maximum in the temperature scale of 120 – 160 °C and then decreased dramatically with the increase of temperature. The resultant PPy/MWNT nanotubes enhanced electrical conductivity and thermal stability of nanocomposite compared to PPy which was strongly influenced by the feed ratio of pyrrole to MWNTs.

STUDY ON PHOTOBLEACHING OF METHYLENE BLUE DOPED IN PMMA, PVA AND GELATIN USING PHOTOACOUSTIC TECHNIQUE

The photobleaching of Methylene blue embedded in the solid matrix PMMA (poly(methylmethacrylate)), PVA (poly(vinyl alcohol)) and gelatin has been investigated using a photoacoustic technique. Photoacoustic signals were measured as a function of time, chopping frequency, and the beam power. Experimental results indicate that the photobleaching rate is proportional to the incident laser power (260–300 mW) and decreased with increasing the concentration of dopant molecules. Methylene blue embedded in PVA shows the highest photobleaching rate then followed by gelatin and PMMA. The increase of photobleaching rate in PVA is also noticed when the beam power is increased. The thermal diffusivity values obtained for bleached PMMA, PVA and gelatin are 1.46 × 10-3cm2/s, 0.83 × 10-3,cm2/s and 1.10 × 10-3cm2/s respectively. Spectrophotometer and Raman spectroscopy were used to confirm the photoacoustic results.

Optical characterization of multi layer thin films using surface plasmon resonance method: From electromagnetic theory to sensor application

Surface plasmon resonance (SPR) is a quantum electromagnetic phenomenon arising from the interaction of light with free electrons at a metal-dielectric interface. SPR has emerged as a powerful optical sensor based on the sensing of the change in refractive index of a medium adjacent to the metal surface layer. In the present work, the data analysis in SPR method which involves determination of optical constants and thicknesses of multi layer thin films was investigated based on Kretschmann configuration. The SPR experimental results (reflectance versus incident angle plots) were analyzed by using Maxwells and Fresnels equations. The calculations involve transfer matrix method where the unknown optical parameters were obtained by fitting experimental SPR plots to calculated theoretical results. The utility of this transfer matrix has also been demonstrated for recently reported SPR experiment on sensor application.