Charotar University of Science & Technology
Gujarat, India

Time filter

Source Type

Shah K.,Charotar University of Science & Technology | Upadhyay R.V.,Charotar University of Science & Technology | Aswal V.K.,Bhabha Atomic Research Center
Smart Materials and Structures | Year: 2012

We compare the magneto-viscous behavior in a shear flow of three different types of magnetic suspension in the presence of a magnetic field. The first suspension contains magnetite particles of average size 10nm dispersed in transformer oil. The second one is made of large sized magnetite particles having 30nm particle size dispersed in transformer oil. The third suspension is a mixture of the first and second fluids in different weight proportions. The size and size distribution have been confirmed by transmission microscopy and small angle neutron scattering experiments. The rheological properties of the first two suspensions were measured for varying shear and field values. The flow behavior of the nanosized dispersed ferrofluid is described with Binghams yield stress model and it varied from 2.2 to 5.5Pa on increasing the field from 0 to 1T. The large sized particle dispersed fluid exhibits magneto-viscous behavior with increasing field. The value of Binghams yield stress obtained is nearly 15 times higher than that of the small size dispersion. On mixing these two fluids with different weight fractions, the Bingham yield stress value increases by a factor of three compared with that of the large sized particle dispersed fluid. The Mason number provides a good scaling of data in the steady simple flow regime. The observed yielding behavior is due to the formation of a longer chain structure in the system under the field and in-field microscopy confirms the same. The present study shows that the addition of large sized magnetic particles in magnetic fluid increases the yield stress as well as the fluid stability under a field. © 2012 IOP Publishing Ltd.

Parekh K.,Indian Institute of Technology Gandhinagar | Upadhyay R.V.,Charotar University of Science & Technology
Journal of Applied Physics | Year: 2010

Static and dynamic magnetic properties of oleic acid/oleyamine coated Mn-Zn ferrite nanoparticles of diameter 82 Å are reported. The zero-field-cooled peak temperature decreases with increasing magnetic field and obeys the well known de Almeida-Thouless line. The zero-field-cooled magnetization data are simulated by assuming noninteracting magnetic particles with uniaxial anisotropy and lognormal particle size distribution. The relevant parameters give the values of particle diameter (D) 80 Å, standard deviation 0.3 in ln(D), and the anisotropy constant K to be 5.8× 10 5 erg/cm3. The observed higher value of standard deviation is due to the interparticle interaction. The complex magnetic susceptibility was measured as a function of temperature for frequencies ranging from 67 to 1800 Hz. The temperature at which the maximum in the ac-susceptibility curve is observed is well accounted by the Vogel-Fulcher law for both χ′ and χ″. The peak is also observed in a plot of χ″/χ′ versus temperature, which may mean the existence of magnetic aftereffect, and furthermore, it has an Arrhenius as well as Vogel-Fulcher law type dependence. An observed nonthermal activation type relaxation mechanism at 12 K is attributed to possible quantum tunneling effect in Mn-Zn ferrite nanoparticles. © 2010 American Institute of Physics.

Andhariya N.,Bhavnagar University | Chudasama B.,Thapar University | Mehta R.V.,Bhavnagar University | Upadhyay R.V.,Charotar University of Science & Technology
Journal of Nanoparticle Research | Year: 2011

The use of nanoparticles as drug delivery systems for anticancer therapeutics has great potential to revolutionize the future of cancer therapy. The aim of this study is to construct a novel drug delivery platform comprising a magnetic core and biodegradable thermoresponsive shell of tri-block-copolymer. Oleic acid-coated Fe3O4 nanoparticles and hydrophilic anticancer drug "doxorubicin" are encapsulated with PEO-PLGA-PEO (polyethylene oxide-poly d, l lactide-co-glycolide-polyethylene oxide) tri-block-copolymer. Structural, magnetic, and physical properties of Fe 3O4 core are determined by X-ray diffraction, vibrating sample magnetometer, and transmission electron microscopy techniques, respectively. The hydrodynamic size of composite nanoparticles is determined by dynamic light scattering and is found to be ∼36.4 nm at 25°C. The functionalization of magnetic core with various polymeric chain molecules and their weight proportions are determined by Fourier transform infrared spectroscopy and thermogravimetric analysis, respectively. Encapsulation of doxorubicin into the polymeric magnetic nanoparticles, its loading efficiency, and kinetics of drug release are investigated by UV-vis spectroscopy. The loading efficiency of drug is 89% with a rapid release for the initial 7 h followed by the sustained release over a period of 36 h. The release of drug is envisaged to occur in response to the physiological temperature by deswelling of thermoresponsive PEO-PLGA-PEO block-copolymer. This study demonstrates that temperature can be exploited successfully as an external parameter to control the release of drug. © 2010 Springer Science+Business Media B.V.

Chudasama B.,Thapar University | Vala A.K.,Bhavnagar University | Andhariya N.,Bhavnagar University | Mehta R.V.,Bhavnagar University | Upadhyay R.V.,Charotar University of Science & Technology
Journal of Nanoparticle Research | Year: 2010

In this article, we describe a simple onepot rapid synthesis route to produce uniform silver nanoparticles by thermal reduction of AgNO3 using oleylamine as reducing and capping agent. To enhance the dispersal ability of as-synthesized hydrophobic silver nanoparticles in water, while maintaining their unique properties, a facile phase transfer mechanism has been developed using biocompatible block copolymer pluronic F-127. Formation of silver nanoparticles is confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV- vis spectroscopy. Hydrodynamic size and its distribution are obtained from dynamic light scattering (DLS). Hydrodynamic size and size distribution of as-synthesized and phase transferred silver nanoparticles are 8.2 ± 1.5 nm (σ= 18.3%) and 31.1 ± 4.5 nm (σ= 14.5%), respectively. Antimicrobial activities of hydrophilic silver nanoparticles is tested against two Gram positive (Bacillus megaterium and Staphylococcus aureus), and three Gram negative (Escherichia coli, Proteus vulgaris and Shigella sonnei) bacteria. Minimum inhibitory concentration (MIC) values obtained in the present study for the tested microorganisms are found much better than those reported for commercially available antibacterial agents.

Phu D.X.,Inha University | Shah K.,Inha University | Shah K.,Charotar University of Science & Technology | Choi S.-B.,Inha University
Smart Materials and Structures | Year: 2014

This paper presents a new adaptive fuzzy controller and its implementation for the damping force control of a magnetorheological (MR) fluid damper in order to validate the effectiveness of the control performance. An interval type 2 fuzzy model is built, and then combined with modified adaptive control to achieve the desired damping force. In the formulation of the new adaptive controller, an enhanced iterative algorithm is integrated with the fuzzy model to decrease the time of calculation (D Wu 2013 IEEE Trans. Fuzzy Syst. 21 80-99) and the control algorithm is synthesized based on the tracking technique. In addition, for the verification of good control performance of the proposed controller, a cylindrical MR damper which can be applied to the vibration control of a washing machine is designed and manufactured. For the operating fluid, a recently developed plate-like particle-based MR fluid is used instead of a conventional MR fluid featuring spherical particles. To highlight the control performance of the proposed controller, two existing adaptive fuzzy control algorithms proposed by other researchers are adopted and altered for a comparative study. It is demonstrated from both simulation and experiment that the proposed new adaptive controller shows better performance of damping force control in terms of response time and tracking accuracy than the existing approaches. © 2014 IOP Publishing Ltd.

Popli S.,Charotar University of Science & Technology | Patel U.D.,M. S. University of Baroda
International Journal of Environmental Science and Technology | Year: 2012

Dyes are synthetic organic compounds widely used in various industries such as, textile, leather, plastic, food, pharmaceutical, and paints manufacturing industries. Coloured effluents are highly toxic to the aquatic life and mutagenic to humans. Wastewater containing dyes has become an important issue demanding serious attention. Among the synthetic dyes, azo dyes are the largest and most widely used dyes and account for more than half of the annually produced dyes. The biodegradation of azo dyes is difficult due to their complex structure and synthetic nature. Several treatments have been proposed for efficient azo dye removal, most of them presenting some limitations such as generation of waste sludge, high operational costs, poor efficiency, and incomplete mineralization. Biological treatment is a cost-effective and eco-friendly process for dye degradation. Sequential anaerobic–aerobic biological treatment is considered as one of the most cost-effective methods for the complete mineralization of azo dyes. The anaerobic stage yields decolourization through reductive cleavage of the dye’s azo linkages, resulting in the formation of generally colourless but potentially hazardous aromatic amines. The aerobic stage involves degradation of the aromatic amines. It is the most logical step for removing the azo dyes from the wastewater. Several factors can influence the microbial activity and consequently the efficacy and effectiveness of the complete biodegradation processes. This paper summarizes the results of biological decolourization of azo dyes using various types of reactors, elaborates biochemical mechanisms involved, and discusses influence of various operational parameters on decolourization based on reports published in the last decade. © 2014, Islamic Azad University (IAU).

Parekh K.,k-Technology | Upadhyay R.V.,Charotar University of Science & Technology
Journal of Magnetic Resonance | Year: 2012

The electron spin resonance (ESR) technique has been applied to study the spin dynamics in broad temperature range for rare earth doped Mn 0.5Zn0.5Fe1.9Gd0.1O4 (MZG5) magnetic fluid. Zero field cooled (ZFC) ESR spectra of MZG5 fluid exhibit an isotropic shift in the resonance field below 40 K, while the field cooled (FC) ESR spectra show a deviation from sin2 θ behavior and an angle dependent hysteresis, this unambiguously points to the dominating unidirectional freezing of surface spins below 40 K. Above 60 K, the resonance field exhibits sin2 θ behavior, indicating the uniaxial anisotropy contribution of core spin. This indicates that surface spin freezing temperature is around 40 K. The presence of surface spin freezing and the coupling between core and surface spins are further supported by cycle dependent FC ESR spectra measured at 20 K, which show the systematic increase in resonance field (Hres) and intensity. The double peak behavior of blocking temperature distribution retrieved from ZFC-FC magnetization measurement is an additional corroboration of the existence of surface spin glass like layer. © 2012 Elsevier Inc. All rights reserved.

Parmar H.,Charotar University of Science & Technology | Desai R.,Charotar University of Science & Technology | Upadhyay R.V.,Charotar University of Science & Technology
Applied Physics A: Materials Science and Processing | Year: 2011

Microwave combustion technique modified by post treatment procedure is used to synthesize single-phase spinel ferrites of cobalt, zinc, and substituted magnetic nanoparticles of typical size 390 Å. The post treatment does not alter the crystal structure but increases the crystallinity. This is confirmed by powder x-ray diffraction and Fourier Transform Infrared (FTIR) studies. Citric acid is used as a fuel. The fresh synthesized sample shows an impurity phase in x-ray and in FTIR. This is due to the unreacted citrate molecule adsorbed on the particle surface. It is shown that by treating the sample with 0.1 M HCl, we can eliminate the impurity phase, and one can obtain a pure single phase. The magnetization at 8 kOe increases by nearly 8% after the removal of impurity. In order to remove surface adsorbed OH - ion, samples are treated with NaCl and heated to 200°C for four hours. The XRD result indicates that after the treatment neither the crystallite size nor the distribution changes, but it removes OH - ion. This is also confirmed by FTIR analysis. Thus, this modified technique can be used to synthesize pure nanocrystalline samples of spinel ferrites. © 2010 Springer-Verlag.

Upadhyay R.V.,Charotar University of Science & Technology | Laherisheth Z.,Charotar University of Science & Technology | Shah K.,Charotar University of Science & Technology
Smart Materials and Structures | Year: 2014

In this work, the effect of particle shape (flakes) on the magnetorheological (MR) properties of an iron based MR fluid, constituted of two different volume fractions of particles dispersed in a liquid carrier, is studied. To compare the MR effect, spherical iron carbonyl particle based MR fluid is studied. In both MR fluids, linear viscoelastic behavior has been extensively investigated using small amplitude oscillatory analysis and magnetic sweep tests, in the presence and absence of a magnetic field (H). The amplitude sweep tests reveal that flake-based MR fluid shows a higher storage modulus compared to sphere-based MR fluid and saturates at a lower magnetic field strength. The variation of storage modulus with magnetic field strength shows an Hn dependence, where n varies from 2.2 to 2.4 for 20% volume fraction while it varies from 1.6 to 2 for a dilute sample. In the case of sphere-based MR fluid, at 20% volume fraction the variation of storage modulus is nearly linear with the magnetic field at low strain amplitude, and with increasing strain amplitude shows H2 dependence. At lower volume fraction in both cases, the loss modulus increases linearly with the magnetic field strength. The observed enhancement in the MR effect in the flake-based MR fluid is likely due to the stronger particle-particle interaction which results in higher friction between the particles. The sedimentation rate decreases by nearly 50% when flakes are used. The study reveals that one can use the irregular shaped particles for MR applications at low fields (∼80 kA m -1). © 2014 IOP Publishing Ltd.

Laherisheth Z.,Charotar University of Science & Technology | Upadhyay R.V.,Charotar University of Science & Technology
Journal of Intelligent Material Systems and Structures | Year: 2016

In this work, the field-dependent rheological properties of the magnetorheological fluid system, featuring plate-like iron particles, at different magnetic fields in quasi-static mode are investigated using MCR 301 magnetorheometer at ambient temperature. At an intermediate field strength, static yield stress exhibits H1.5 dependency, eventually becoming field independent at higher field. Later on, the temperature-dependent properties are analysed at the different magnetic field intensities. Observational data are obtained from magnetic field ranging from 0.0 to 1.1 T and in the temperature range 30°C-120°C. It is noted that at low field strength, the static yield stress increases initially with temperature and decreases with further increase in temperature. A yield stress model is suggested based on the average normalized sensitivity and magnetic field to describe the measured variation in the magnetorheological fluid response at higher temperature. This information will be useful for predicting thermal sensitivity of device performance. © The Author(s) 2015.

Loading Charotar University of Science & Technology collaborators
Loading Charotar University of Science & Technology collaborators