Solid State Phenomena Vol. 111

Abstract: We have attempted to realize new biomolecular-inorganic nanohybrids with two different functions, one from inorganic moiety and the other from biological one. Recently we were quite successful in demonstrating that a two-dimensional inorganic compound like layered double hydroxide (LDH) can be used as gene or drug delivery carriers. Such inorganic vectors are completely new and different from conventionally developed ones such as viral-based, naked, and cationic liposomes, those which are limited in certain cases of applications due to their toxicity, immunogenecity, poor integration, and etc. But the mentioned problems can be overcome by synthesizing inorganic vectors properly with non-toxic metal ions having biological compatibility. Since LDHs with positive layer charge have an anion exchange capacity, functional biomolecules with a negative charge can be intercalated into hydroxide layers of LDH by a simple ion-exchange reaction to form a bio-LDH nanohybrid. We also found that the hydroxide layers of LDHs could protect the intercalated molecules very efficiently. If necessary, inorganic materials, as reservoir and delivery carrier, can be intentionally removed by dissolving it in an acidic which offer a way of recovering the encapsulated biomolecules. The possible roles of inorganic lattice as the gene and drug delivery carrier will be shown by demonstrating the cellular uptake experiments of FITC, fluorophore, with laser scanning confocal fluorescence microscopy. A

Abstract: MZFC, MFC magnetizations, χac susceptibility and resistance measurements have been carried out for various polycrystalline compounds of (AA’)(BB’)O3 perovskites with A = La, (Nd,Y); B = Mn,Co; A’ = Sr,Ca and B’= Fe, Ti. Analyses have been done to elucidate the metallic ferromagnetism (FM) established by Double Exchange interaction between B+3 ion and the B+4 ion that is induced by the substitution of A’ for A. It is shown that there is no ‘pure’ FM ordering existing in the compounds, in other words the materials consist of a FM and a non-FM phase. In case when the latter is an AFM phase, the coexistence and competition of the two phases result in spin-glass like appearances. Such phenomena have been observed in several compounds of both single- and/or mixed-element at B site. The studies on substitution of Mn for Co in La0.7Sr0.3Co1- yMnyO3 show no DE interaction between the two magnetic ions, which results in not only SG behavior at y = 0.1 concentration but a clear evidence on a phase separation in the high y region. An analysis of M(H,T) curves for this region suggests a structural scenario that the FM phase forms as islets (of volume fraction as small as 2.7 – 8.6%) embedded in isolating AFM matrix. For the case while B’= Ti the inhomogeneity evidence appears as an enhancement of the Low Field MagnetoResistance, which is commonly understood as an intergranular effect.

Abstract: Ca2+-containing porous gelatin-siloxane hybrids were prepared using sol-gel process, post-gelation soaking, and freeze-drying. The porosity and pore size of the hybrids could be well controlled by the freezing temperature and the pH value of the soaking solution. The pore characteristics were related to the structure change during the soaking treatment. A bone-like apatite layer was able to form in the Ca2+-containing porous gelatin-siloxane hybrids upon soaking in a stimulated body fluid. The porous gelatin-siloxane hybrids could release gentamicin sulfate which is an antibiotic drug in bone chemotherapy. Thus, those hybrid materials are proposed to find application as novel bioactive and biodegradable scaffolds in bone tissue engineering.

Abstract: Most of the gases detecting metal oxide semiconductors are operated at temperatures above 250oC. It is not energy efficient for MOS gas sensors to operate at such high temperature. To solve this problem, research and investigations are trying to obtain new MOS sensing materials that can operate at ambient temperature. In this study, gas sensing materials consisting of MOS and carbon nanotubes (CNTs) are developed for detecting gases at lower temperature. The hybrid system, MWCNTs/TiO2, demonstrates the possibility of detecting the gases at ambient temperature with high energy efficiency.

Abstract: A better efficiency of sensing tera-hertz signals (T-rays) depends on a better crystalline structure which is obtained by replacing a small amount of Cd on Zn sites of ZnTe crystals. Zn1-xCdxTe (ZCT) crystals were fabricated with an advanced vertical Bridgeman method and the structural properties of the ZCT crystals were studied with high resolution x-ray diffraction (HRXRD) and x-ray absorption fine structure (XAFS) measurements. The Rietveld refinement to the HRXRD data showed that the ZCT crystals at x ~ 0.05 were slightly less disordered than the ZnTe crystals. These results were confirmed by the XAFS data analysis. The better structural orderings can be directly related to the sensing and emitting efficiencies of T-ray by the ZCT crystals.

Abstract: Studies on ZnxCu1-xBi2O4(0≤ x ≤0.6) spinels (S1-S5: x = 0.0, 0.15, 0.3, 0.45, 0.6) were done using varieties of structure sensitive techniques. The powder X-ray diffraction (XRD) studies shows formation of cubic phase, a=10.6023 Ǻ, space group, Ia3, Z=3 in all the samples. The IR spectral results show the presence of octahedral[CuO6/2] or [BiO6/2] units and Bi-O, Cu-O, and Zn-O bonds in the samples. From the trend g║>g┴>ge(ge=2.0023) obtained from electron paramagnetic resonance(EPR) lineshapes simulation we conclude that the paramagnetic site in these glasses is Cu2+(3d9) which is in a tetragonally elongated octahedron [O1/2-CuO4/2-O1/2] exhibiting Jahn-Teller distortion having D4h symmetry with orbital singlet 3dx 2-y 2(2B1g) as the ground state.

Abstract: Titanium alloy is an attractive material for aerospace and automobile applications due to its lightweight and high strength. Titanium metal matrix composite (MMCs) is one of the promising materials which could be employed to enhance stiffness and wear resistance of titanium alloy. In this study, reinforcement of in-situ and ex-situ particulates has been investigated. The experimental results show that a dense microstructure with uniformly distributed in-situ TiB reinforcement phase in the Ti+B+Sn system could be obtained. It is present in either needle or blocky shape. This process involved warm pressing of mixed powder in semi-solid stage followed by sintering, which eliminated costly CIP and HIP processes. However, it is found that the ex-situ particulates in the titanium metal matrix are not suitable as reinforcements in Ti-Sn metal matrix as they either reacted with titanium during sintering process or generated a void at the interface between the reinforcement and the matrix.

Abstract: In this study, pure aluminum reinforced with interconnected galvanized iron mesh and Ni particulates was synthesized using an innovative disintegrated melt deposition technique followed by hot extrusion. Microstructural characterization of composite samples showed uniform distribution of Ni and Al-Ni based intermetallic particulates in the matrix material, good interfacial integrity of aluminum matrix with iron mesh and Ni particulates and the presence of minimal porosity. Results of thermal mechanical analysis indicate a decrease in the average coefficient of thermal expansion of the aluminum matrix with the use of hybrid reinforcements. Mechanical characterization also revealed that the coupled use of galvanized iron mesh and Ni particulates lead to an improvement in the hardness, dynamic modulus, 0.2% yield strength and UTS but ductility was adversely affected. An attempt is made to correlate the use of hybrid reinforcements with the improved properties exhibited by the synthesized composites.

Abstract: To improve the thermal and mechanical properties of polyimides, a nanocomposite of naphthalene containing polyimide (PI) was hybridized with Montmorillonite (MMT). The PI was synthesized from a diamine, 2,7-bis (4-aminophenoxy) naphthalene and polymerized with a 3,3’,4,4’-benzophenone tetracarboxylic dianhydride via thermal imidization. PI-MMT nanocomposites were then prepared from a DMAc solution of poly(amic acid) precursor and a DMAc dispersion of MMT which were organo-modified with various amount of n-dodecylamine. Characterization results demonstrated that the introduction of a small amount of MMT (up to 5%) led to enhanced thermal stability and mechanical properties of PI. The 5% weight loss temperature in N2 was increased by 46oC in comparison to pristine PI with an organoclay content of 5%. The CTE and dielectric constant were decreased. However, at organoclay contents higher than 5% these properties were reduced because the organoclay was poorly dispersed and resulted in aggregate formation.

Abstract: Heterophyllosilicates are mineral phases based on layers that are comparable with those of the better known TOT phyllosilicates. Precisely, the HOH layers occurring in the heterophyllosilicates are formally obtained from a TOT layer by periodically introducing five or six co-ordinated titanium in the silicatic T sheets that sandwich the octahedral O sheet. The structural analogy between smectites, from which the mesoporous pillared clays are prepared, and heterophyllosilicates suggests that in principle pillared materials based on HOH layers could be prepared. Field observations show that swelling can occur in heterophyllosilicates; however, these minerals are rare and their synthetic analogues must first be prepared before attempting pillaring, an operation that might lead to interesting results for materials science owing to the presence of titanium.