Scientia Iranica
Volume:17 Issue: 2, 2010

The aim of this study is the evaluation of the effect of microencapsulation of nanoparticles in composite microparticles on the reduction of burst release. Microparticles (simple and composite) and nanoparticles were prepared by using water-in-oil-in-water (W/O1/W2 double-emulsion solvent diffusion/evaporation method), using different drug/polymer ratios. For preparation of the composite microparticle, nanoparticle suspension was used as the internal phase. In this investigation, the microparicle, nanoparticle and composite microparticle formulations prepared were characterized by loading efficiency, yield, particle size, zeta potential, XRD (X-ray Diffractometry), FTIR (Fourier Transform Infrared Spectroscopy), DSC (Differential Scanning Calormetry) and drug release. The best drug of the polymer ratio in the microparticle and nanoparticle were F3 (0.4:1) and NP1 (0.1:1), which showed 26.89% and 9.07% of entrapment, loading efficiency 94.2 %, 99.44% and mean particle size 13.114 m and 756 nm, respectively. The drug loading microparticle, COM3 (nanosuspension with 0.2.:1 drug/polymer ratio), showed 28.56% of entrapment, loading efficiency 99.96% and mean particle size 13.013 m. The burst was significantly lower with composite microparticles and may be explained by the slower di usion of the drugs through the double polymeric wall formed by the nanoparticle matrix, followed by another di usion step through the microparticle polymeric wall.

The uses of carbon nanotubes (CNTs) in nanotechnology and leading industries are of extreme importance and they have many applications. One such application is producing nanotube thin pages called buckypaper. These pages, known as nanotube sheets, have signi cant physical, chemical, mechanical, thermodynamic and electromagnetic properties, such as being several times stronger than steel. In spite of e orts devoted to the development of procedures for the production of buckypaper, not many attempts have been made to understand their mechanical behavior. Computer simulations can be used as a powerful tool to discover the mechanical properties of these materials. The aim of the present research is to investigate the mechanical behavior of buckypaper using the nite element method. Toward this goal, the molecular network of buckypaper, which consists of a regular arrangement of CNTs, is modeled as a structure with its atoms as nodes, its bonds as 3-D-beam elements and Van der Waals forces by means of nonlinear forces. A computer program is then developed to calculate the mechanical properties of buckypaper especially the modulus of elasticity. In this program, the nanotubes are arranged together to create a simple ordered network with periodic boundary conditions resembling real buckypaper. The obtained results from this procedure are compared with those derived from molecular mechanics.

SiO2 substrates, and then annealed at 400C. Deposition was performed in a Ar + O2+N2 gas mixture of 1.0 Pa, and oxygen and nitrogen with constant pressures of 0.2 Pa and 0.1 Pa, respectively. The thicknesses of deposited layers, TiO(2􀀀x)Nx/TiO2/ZnO, were approximately 200 nm, 800 nm and 80 nm, respectively. ZnO was used as a bu er layer. The structure and morphology of the deposited lms were evaluated by X-Ray Di raction (XRD) and scanning electron microscopy (SEM). The average grain sizes of TiO2 and nitrogen doped annealed thin lms were 25 and 18 nm, respectively. The microstructure of the annealed lms was anatase. The optical transmittance of the lms was measured using ultravioletvisible light (UV-vis) spectrophotometer. The photocatalytic activity of the samples was evaluated by the degradation of Methylene Blue (MB) dye.

magnetoelectric composite composed of PZT as a piezoelectric material and Co-50%Fe as a magnetostrictive alloy was produced. The Pb (Zr0:52Ti0:48) O3 (PZT) layer was deposited on a magnetic alloy via sol gel spin coating and Pulsed Laser Deposition (PLD) processes. The results show that the sol gel prepared PZT lm exhibits a single perovskite phase, but the sample prepared using, the PLD method, is susceptible to creating a pyrochlore phase. The prepared PZT lms demonstrated good dielectric properties and have large potential applications in multifunctional devices. Based on acceptable electrical and magnetic properties «r of 894 and magnetostriction coefficient of 70  10􀀀6, it seems that these samples will have also good magnetoelectric properties.

The realization of nano and micro-sized, highly-featured, 3-dimensional structures on Si substrates is reported where a single mask in a hydrogen-assisted deep reactive ion etching is exploited. Three main gases of oxygen, hydrogen and SF6 are used in a sequential passivation and etching process to achieve high aspect ratio features. The ows of gases, and the plasma power and timing of each subsequence are the main parameters to achieve the desired three-dimensional etching by controlling the under-etching and recovery steps, which leads to the formation of unique features directly on silicon substrates. Depending on the plasma power, etch-rates as high as 0.75 m/min can be obtained. The plasma power can reach a high value of 1 W/cm2 over a large area of 20  15 cm2. In addition, features with a controllable under-etching and a recovery with more than 8 m in the sidewall recession have been achieved. Furthermore, values of aspect ratios higher than 40-50 can be obtained. The formation of nano-wall features is also reported.

Silica aerogel-multi wall carbon nanotube composites were synthesized successfully with a waterglass precursor and an ambient pressure drying method. Pure silica aerogels are so fragile that they cannot be used easily. Carbon nanotubes (MWCNT) were used as reinforcements to strengthen the mechanical properties of pure silica aerogels. Results show that inserting small amounts of MWCNT causes silica aerogels to monolith. By addition of MWCNT, monolith nanocomposites were produced with 800 m2/g surface area and a 140contact angle. Results show that the silica aerogels and reinforced composites have an excellent adsorption property for the removal of organic pollutants from water. The average adsorption capacity was about 5 times the composite weight for benzene, toluene, n-Hexane, kerosene, gasoline and petroleum. The adsorption isotherm was type IV for pure silica aerogels and nanocomposites, which is ideal for excellent adsorbency. Addition of MWCNTs will not decrease the pollutant adsorption capacity of the aerogels. TEM, SEM, FTIR, contact angle, BET, BJH and the porosity of pure silica aerogels and nanocomposites are measured and reported. Adsorption isotherms show that synthesized adsorbents obey the Freundlich isotherm equation.

This paper introduces a new approach for complete drift modeling and compensation for Scanning Probe Microscopes (SPMs) as conventional nanorobots. Although, before this, drift was described as remained error after hysteresis and creep compensation, it can seriously affect SPM performance. Since experimental work accentuated that thermal strain has a dominant contribution, the present model includes only thermal effects. As a signi cant contribution, an analytical relationship is introduced for heat generation in piezotubes. Then, based on classic heat transfer, the thermal drift for the piezoscanner and microcantilever is modeled. As sub-micro (nano) parts for tip and interfaces in nanoimaging and nanomanipulation modes, the thermal circuit is introduced. Finally, the transfer functions of thermal drift versus ambient temperature variations and piezoscanner heat generation are derived. In this paper, it is not assumed that drift velocity is constant, whereas this assumption was a major drawback of previously presented procedures. This paper, by introducing a comprehensive model and an approximated analytical model, and comparing existent experimental results, shows that the present model is effective and mathematically traceable in both modes.

A sensitive colorimetric method for the detection of ascorbic acid was proposed in this research based on the reduction of silver ions by ascorbic acid in the presence of citrate-stabilized silver seeds, additional trisodium citrate and a polymer such as polyvinylpyrrolidone. The color of the stable sol is controlled by varying the concentration of trisodium citrate (TSC), polyvinylpyrrolidone, silver nitrate and silver seeds. The reduction of Ag+ to triangle silver nanoparticles (Ag-NPs) by ascorbic acid in the presence of trisodium citrate (TSC) and silver seeds produced two very intense surface plasmon resonance peaks of Ag-NPs. The plasmon absorbance of Ag-NPs allows the quantitative spectrophotometric detection of the ascorbic acid. The calibration curve derived from the changes in absorbance at  = 427 nm was linear, with the concentration of ascorbic acid in the range of 6:010􀀀6 to 8:010􀀀5 M. The method was applied to the determination of ascorbic acid in pharmaceutical formulations with satisfactory results.

The growth of submonolayer metallic or molecular nanostructures via ion-beam sputtering onto reconstructed semiconductor surfaces, followed by in-situ scanning probe imaging of the formed nanostructures, give an interesting insight into developing new molecular multifunctional nanoarchitectured materials for various applications. The case of pentacene, as one of the most important candidates in the eld of organic thin lm electronics, molecules and also Au metallic nanostructures, deposited in the submonolayer regime onto a reconstructed InP (0 0 1) surface, is discussed in view of the observed growth modes, structure and topology. During initial stages of growth, a uniaxial di usion channel dominates, and long pentacene molecular chains self-organize parallel to the [110] crystallographic direction on the InP surface. The study is performed by in-situ non-contact atomic force microscopy investigations with atomic resolution. It is shown that the self-assembling of molecular structures onto at terraces is dependent on the atness and orientation of the terraces reconstructed onto the semiconductor surface. Moreover, it is possible to create functional molecular nano-architectures by nano-manipulation of single molecules with the AFM tip. This procedure may have a large impact on technological applications, such as organic TFT and molecular nanowires.