Sharif Digital Repository

In this paper, the use of colloid chemistry in the synthesis of 5 A° lead sulfide semiconductor nanoparticles has been described. Here, hydrogen sulfide gas dissolved in water is used for the chemical reaction, instead of purging the H2S gas into the solution, which has an influence on particle size. In this technique, the growth of particles was controlled by the addition of EDTA. A fast evolution of the optical absorption spectrum demonstrated the following synthesis. Soon after synthesis reaction, the sample exhibits a structural absorption spectrum with one well-defined peak in a 240 nm wavelength. The absorption spectrum shows a featureless structure, with no tail near the absorption... 

Liquid crystal colloids have been proposed as suitable candidates for responsive photonic crystals. Large scale growth of such colloidal systems is, however, a challenge and recently template-assisted assembly has been proposed to guide the growth of colloidal crystals, with controlled symmetries, in nematic liquid crystals. Known for their long-range anisotropic interactions, these colloidal systems are stabilized typically at the center of the cells due to strong particle-wall repulsion from the confining substrates. This behaviour is dramatically changed in the presence of topographic patterning. Here we propose the use of topographic modulation of surfaces to select and localize... 

The effective interaction between spherical colloids in nematic liquid crystals is investigated in the framework of the Landau-de Gennes theory. The colloids differ in their surface interaction with the nematic liquid crystal. The particles induce quadrupolar far-field distortions in the nematic matrix, favouring homeotropic and the other degenerate planar anchoring of the nematic director. In the strong anchoring regime the colloids with homeotropic anchoring are accompanied by an equatorial disclination line defect, known as "Saturn-ring", while the colloids with degenerate planar anchoring nucleate a pair of antipodal surface defects, called "boojums". In the linear (large-distance)... 

The dynamical scattered light intensity and multiplicative cascade model was employed to characterize the anisotropic charged colloidal particles suspension during the so-called Sol-Gel transition. Generally we looked for finding a criterion to distinguish the properties of Sol and Gel states systematically. The probability density function (PDF) of the light scattering intensity shows an obvious change with proceeding of the sample aging process (during of gelation state). Our results confirmed that in the so-called Sol state, the value of non-Gaussian parameter, kW, as a function of time is larger than that of for weak-Gel or in coexistence Sol-Gel state. The number of cascades in the... 

Application of light-weight drilling fluids is essential to develop depleted hydrocarbon reservoirs. Recently, colloidal gas aphron (CGA)-based fluids have been introduced for such applications due to their ability in controlling fluid losses. In this work, a comprehensive experimental study was performed to choose the best formulation for CGA fluids by implementing static stability tests, rheological behavior measurements, and bubble size analyses of CGAs. Xanthan gum polymer and sodium dodecyl benzene sulfonate (SDBS), an anionic surfactant, and cetyl trimethyl ammonium bromide (CTAB), a cationic surfactant, were utilized to prepare CGAs. For the range of experiments conducted, the... 

Colloidal nanoparticle could be used for recognition location of tumors and cancer tissue. A simulation of molecular dynamic for colloidal silver nanoparticles (Ag NPs) based on density functional theory (DFT) potential parametrization with different sizes in 1-ethyl-3-methylimidazolium hexafluorophosphate [EMim][PF6] ionic liquid was performed. Then, using Green Kubo formalism, diffusion coefficient for Ag NPs in IL and in the gas phase was calculated. We also calculated diffusion coefficients of anions and cations for pure IL and IL in the presence of different sizes of Ag NPs at different temperatures. The findings showed that the diffusion coefficient of anions and cations increases in... 

Field-effect transistors have been widely used to study electronic transport and doping in colloidal quantum dot solids to great effect. However, the full power of these devices to elucidate the electronic structure of materials has yet to be harnessed. Here, we deploy nanodielectric field-effect transistors to map the energy landscape within the band gap of a colloidal quantum dot solid. We exploit the self-limiting nature of the potentiostatic anodization growth mode to produce the thinnest usable gate dielectric, subject to our voltage breakdown requirements defined by the Fermi sweep range of interest. Lead sulfide colloidal quantum dots are applied as the active region and are treated... 

A solution-processed, bottom-up nanowire network electrode is developed and employed in a bulk heterojunction colloidal quantum dot solar cell. The electrode features a ZnO template which is converted into locally connected, infi ltratable TiO2 nanowires. The new electrode allows the application of a thicker light absorbing fi lm without compromising the charge extraction, as reported by Edward H. Sargent, Ghassan Jabbour, and co-workers on page 1769. The frontispiece shows schematically the electrode shape and the resultant device architecture  

The influence of particle size and surface modification on sonocatalytic activity of TiO2 nanoparticles was investigated by measuring the degradation efficiency of methyl orange (MO) as a model pollutant. Crystalline TiO2 nanoparticles with different particles and aggregate size were prepared through solution-phase method with varying synthesis temperatures. Coating with polyvinyl alcohol was performed to enhance colloidal stability of the particles over a wide range of pH values (1.5–7.5). Characterization was carried out using X-ray diffraction, high-resolution transmission electron microscopy, dynamic light scattering, and Fourier-transformed infrared techniques. It was found that... 

In the recent years, many researchers have been interested in nanoparticles because of their unique properties. In this study, a method for producing ZnO nanoparticle colloids is proposed. The colloids were characterized by spectroscopic analyzer. By absorption spectrum study, we found out that colloids were consisted of nanoparticles with less than 10 nanometer size. The quantum confinement effect in these spectrums was recognized through blue shift of onset absorption wavelengths. These wavelengths shift from 370 nm to 340 nm by decreasing the particles size. Transmittion electron micrographs showed formation of zinc oxide nanoparticles  

Recently, it was found that ultrasonic wave technology can be used as a method for asphaltene deposits removal from the near wellbore region. However, ultrasounds can affect asphaltene resolution.In this work, asphaltene resolution in several crude oil samples exposed to ultrasonic waves for different time intervals is studied by confocal microscopy. The colloidal structure of flocks is described by analysis of asphaltene particle size distribution to investigate ultrasonic application in solving asphaltene deposition problems.. The results show that for the first 90 minutes of flocculation time, the size of aggregates increases rapidly, and reaction limited aggregation model matches well... 

Gold (Au) nanoparticles are widely used in diagnosing cancer, imaging, and identification of therapeutic methods due to their particular quantum characteristics. This research presents different types of aqueous models and potentials used in TIP3P, to study the effect of the particle size and density of Au clusters in aquatic environments; so it can be useful to facilitate future investigation of the interaction of proteins with Au nanoparticles. The EAM potential is used to model the structure of gold clusters. It is observed that in the systems with identical gold/water density and different cluster radii, gold particles are distributed in aqueous environment almost identically. Thus, Au... 

Laser ablation of titanium target in distilled water for synthesis of colloidal nanoparticles is studied both experimentally and theoretically. The effects of laser parameters such as wavelength, pulse energy, fluence and shot numbers on the ablation rate and size properties of colloidal nanoparticles are investigated. The experimental approach addresses the interesting issue for finding the optimal main experimental parameters of laser ablation. The theoretical thermal model of nanosecond pulsed laser ablation is developed to visualize the evolution of temperature distributions and ablation depth. The simulation result of ablation depth has been compared with the experimental result... 

The electrohydrodynamic (EHD) 3D printing technology is an Additive Manufacturing (AM) method that can be used in the manufacture of submicron-size structures. In this process, which is based on the formation of Taylor jet from a metallic ink, the investigation of particles reaction and aggregate formation in ink during printing is of great importance. In this paper, a new Finite Element model based on particle tracing in fluids is presented that couples the different physics that govern an EHD phenomenon. Vortex flow caused by boundary shear stress was observed in the ink jet; which was more like the Marangoni phenomenon in a stationary drop. By experimentally validating the presented model... 

Recently, ultrasonic wave technology has received much attention as a method for removal of asphaltene deposits from the near wellbore region. However, very little is known about another feature of this technology on the kinetics of asphaltene molecules aggregation. In this work, the kinetics of asphaltene flocculation in several crude oil samples exposed to ultrasonic waves for different time intervals is studied by confocal microscopy. The colloidal structural evolutions of flocks are described by analysis of size distribution of flocculated asphaltene particles. The results show that for the first 90 min of flocculation time, the size of aggregates increases rapidly, and a... 

In this study, colloidal tungsten oxide nanoparticles were fabricated by pulsed laser ablation of tungsten target using the first harmonic of a Nd:YAG laser (1064 nm) in deionized water. After ablation, a 0.33 g/lit HAuCl4 aqueous solution was added into as-prepared colloidal nanoparticles. In this process, Au3+ ions were reduced to decorate gold metallic state (Au0) onto colloidal tungsten oxide nanoparticles surface. The morphology and chemical composition of the synthesized nanoparticles were studied by AFM, XRD, TEM and XPS techniques. UV-Vis analysis reveals a distinct absorption peak at ∼530 nm. This peak can be attributed to the surface plasmon resonance (SPR) of Au and confirms... 

An accurate and fast method for guided modes extraction in monolayer colloidal crystals and their inverse replicas is presented. These three-dimensional structures are composed of a monolayer of spherical particles that can easily and simply be prepared by self-assembly method in close packed hexagonal lattices. In this work, we describe how the guided modes, even or odd modes and light cone boundary can be easily determined using phase variations of reflection and transmission coefficients. These coefficients are quickly calculated by Fourier modal method. The band structures are obtained for a monolayer of polystyrene particles and two-dimensional TiO2 inverse opal by this proposed method  

A novel magnetic nanocarrier with long spacer length and high colloidal stability has been prepared for effective delivery of doxorubicin (DOX). First, poly(amidoamine) (PAMAM) dendrimer was grown up onto the surface of superparamagnetic iron oxide nanoparticles to increase the loading amount of amine groups. Then, terminal amine groups were functionalized by polyethylene glycol dimethylester to increase the spacer length. Then anticancer drug DOX was covalently attached onto the system by hydrazone bond to forms a pH-sensitive nanocarrier. This system is designed to combine the advantage of magnetic targeting, high drug loading capacity, and controlled release