Advanced Materials Research Vols. 93-94

Abstract: In the authors' laboratory, fern-like fractals have been cultured in polymer electrolyte membranes of polyethylene oxide (PEO) doped with ammonium iodide (NH4I). The simulation study was then carried out utilizing the Diffusion Limited Aggregation (DLA) based on random motion of aggregating particles modelling technique. The fractal dimension values and the forms of the simulated fractals are comparable to those observed in the PEO polymer membranes. These indicate that the simulation using the DLA model done in this study has resulted outputs that are in abidance with the original fractals cultured in the polymer membranes.

Abstract: The graft copolymerization is one chemical modification methods to improve natural rubber (NR)’s properties via both solution and latex phases. To enhance the polarity of NR, methyl methacrylate (MMA) was applied for graft copolymerization of NR in the presence of thermal or redox initiators. However, the conventional graft copolymerization generally spends long reaction time (ca. 6-8 h). Due to less energy consumption with faster heating rate, the microwave irradiation was used to induce graft copolmerization of MMA onto NR latex using redox initiation system. By comparing with the conventional grafting method at the same grafting properties, the graft copolymerization of MMA onto NR induced by microwave at 100 W spent the shorter reaction time ca. 15 min; whilst, the conventional method required the longer reaction time as 7 h. The influence of microwave power on the grafting properties was investigated. The structure of graft product was also analyzed by using FTIR and 1H NMR spectroscopy.

Abstract: Subwavelength gratings (SWGs) that consist of net-grid structure are designed as infrared reflectors in this paper. By rigorous coupled wave approach (RCWA) and finite difference time domain (FDTD) method, we simulate its reflectivity which can reach 99.98% at 1.55μm while maintaining reflectivity higher than 99% across the 1.47-1.59μm wavelength range. We introduce SWG reflectors as the bottom mirrors in resonant cavity enhanced photodetectors (RCE PDs). RCE PD's quantum efficiency is increased to 95.7% at 1.55μm and the device has a significant size reduction compared with only using DBR bottom mirror.

Abstract: The polarization switching transients of spray-deposited ferroelectric (NH4)0.39K0.61NO3 (NKN) films have been investigated. Modified Sawyer-Tower circuit has been used to trace the hysteresis loop (P-E). The value of maximum polarization, Ps and coercive field, Ec was found to be 6.58 µC/cm2 and 4.10 kV/cm respectively. The polarization fatigue study has been carried out. The experimental polarization switching transients were fitted well with the Kolmogorov-Avrami-Ishibashi (KAI) nucleation theory The maximum polarization switching current (imax) and maximum switching time (tmax) have been measured as a function of the applied field. The activation field (), dimensionality (n) and switching time have been determined by employing the KAI model to the experimental switching transients. The atomic force microscopy (AFM) has been employed to estimate the grain size (~ 72 nm) and root mean square roughness (rms) (~ 130nm) of the (NH4)0.39K0.61NO3 films and has been correlated with the switching properties.

Abstract: In this study, in vitro acellular bioactivity and tensile bonding strength of hydroxyapatite (HA) coating synthesized by sol-gel technique after long-term storage in simulated body fluid (SBF) for up to 32 days were studied. After soaking in SBF, it was observed that new bone-like apatite layer was formed on the coating indicating the bioactive nature. Bonding strength of sol-gel coated rods was found to decrease with soaking times, from 55 to 30 MPa. In comparison to adhesive bonded titanium rods which were used as control specimens, the values were found to be equal or even greater in certain soaking periods. Debonding at adhesive-titanium interface was the failure mode indicating that the coating is still intact. Therefore, it could be concluded that this sol-gel coating is bioactive and the coating adhesion to substrate is sufficiently strong.

Abstract: Influence of using different layer thickness in three dimensional printing process of calcium sulfate based sample prior to phosphorization process was studied. Phase composition and mechanical properties of the resulting structure were characterized by x-ray diffraction and three-point bending techniques. It was seen that transformation rate, phase composition and flexural strength were all affected by the change in layer thickness. Too high layer thickness, 0.2 mm, caused the disintegration of sample during phosphorization while too low layer thickness, 0.08 mm, decreased the transformation rate. The optimised layer thickness in this study which gave both high conversion rate and flexural properties was found to be 0.1 mm.

Abstract: New hybrid macroporous scaffolds of polycaprolactone (PCL)/tricalcium phosphate (TCP) were developed by taking into account mechanical properties of the bone to be replaced. FTIR spectra indicated the coating of TCP onto the polymer, providing hydrophilic surfaces necessary for cells to attach. As determined by DSC, the depression of PCL melting point suggested a uniform distribution of PCL within the TCP matrix. SEM micrographs revealed pores of irregular shapes varying from 100-200 µm in size in the resultant structures. Indeed, the pore morphology was precisely determined by the leached particles. The scaffolds could tolerate the impact of at least 5.6 kNm2, making them suitable for use as artificial bones of skull, clavicle and ribs. Rat bone stroma attached and survived on the scaffolds, indicating biocompatible of the used materials. Therefore, the prepared scaffolds would be applicable for bone tissue engineering in the near future.

Abstract: Mass attenuation coefficient, total interaction cross-section and effective atomic number of xPbO:(100-x)SiO2, where 30 x 70 (% weight), glass system have been investigated at 662 keV on the basis of the mixture rule. The results are in good agreement with the theoretical values, calculated by WinXCom. The mass attenuation coefficient increases with PbO content, due to higher probability of photoelectric absorption in glass. However, Compton scattering gives dominant contribution to the total mass attenuation coefficient for the glass samples studied. The shielding properties of the glass samples are also better than ordinary shielding concretes and commercial window glasses. These results indicate that the glass systems prepared in this study has a potential to be used as radiation shielding materials.

Abstract: This paper presents the technique that can considerably improve basicity and transesterification activity of calcined natural calcite. Calcined calcite was refluxed in water followed by the calcinations at 600 oC. The characterization results indicate that this procedure substantially increases both the specific surface area and the amount of basic site. Hydration and subsequent calcination also generates a new calcium oxide with less crystalline. ME content was enhanced to 93.9 wt% in 1 hr from 75.5 wt% of calcined calcite. The results imply that the active sites produced by the calination of hydrated sample at 600 oC have higher basicity than those generated from calcinations of fresh calcite at 800 oC. The present study provides new insights for improving catalyst activity by tailoring the preparation conditions.

Abstract: This study focused on investigating the Nd:YAG laser perforation process of several common plastic films including biaxially-oriented polypropylene (BOPP), biaxially-oriented polyethylene terephthalate (BOPET) and low density polyethylene (LDPE) films. Films were perforated under various pulse energies of 50, 150 and 250 mJ and with pulse duration of ~10 ns and pulse repetition of 1 Hz. It was found that, BOPP, BOPET and LDPE films could be perforated using our developed Nd:YAG laser perforating system. Perforation width or diameters of all films increased with increasing pulse energies. Observed perforations were different among the three film types. For instance, at the pulse energy of 150 mJ, average microperforation diameters of BOPP, BOPET, and LDPE were 51.9, 57.5, and 31.0 microns, respectively. Overall results clearly demonstrated that a Nd:YAG laser perforation process used in this study was effective in developing breathable packaging films with tailored oxygen permeation property. Commercial BOPP films containing 200-1,400 micro-perforations/m2 (average perforation diameter of  50 µm) showed a significant improvement in oxygen transmission rates (OTR) of 25-700% over that of the regular BOPP. Very high OTR films of 16,000 cc/m2.day could be effectively produced for the micro-perforated BOPP, where OTR values of close to 20,000 cc/m2.day was obtainable in the case of BOPET films.