Effect of Process Variable on the Gelation Time of Sulfonated Polyacrylamide Nanocomposite Hydrogel

Among the methods available to reduce water production during oil recovery, injecting a gelling system composed of a polymer and a crosslinker has been widely used. In this study, a Plackett-Burman design was used for screening a large number of factors such as concentrations of polymer, crosslinker, pH, temperature, and presence or absence of NaCl, CaCl₂, MgCl₂, KCl, thiourea, sodium lactate, and nanoclay on the gelation time of sulfonated polyacrylamide nanocomposite hydrogels by rheological tests. Among these factors, temperature, pH, and CaCl₂ concentration were found to have the greatest effect on the gelation time. The effects of these three factors and their interactions on the gelation time were then determined by using central composite design of response surface method. As a result, the interactions of CaCl₂ concentration with temperature and pH were considerably more than the interactions of pH and temperature on the gelation time. At low pH (3 < pH < 7), the gelation time decreased by decrease of pH while at CaCl₂ concentration of 3750–11250 ppm and at 7 < pH < 11, the gelation time increased with the increase of pH. It was found that temperature was the most effective parameter to control the gelation time.     

Study of Salinity and pH Effects on Gelation Time of a Polymer Gel Using Central Composite Design Method

Experiments were conducted to investigate the main effects of salinity (NaCl) concentrations and pH factors and their interactions on the gelation time response of a polymer gel used in a water shutoff system in oil field reservoirs. Central composite design (CCD) was used to design experiments and a mathematical model building. The main advantage of CCD was to generate the quadratic mathematical model for the gelation time as functions of salinity and pH factors. Tests were limited and optimized by CCD points including low star (axial), low factorial, central, high factorial, and high star points. The evaluation of the data and the developed model were performed through the examination of graphical trend of residuals and a numerical approach. Analysis of variance (ANOVA) was used to estimate the amount of data variations from the model predictions. It was found that the model was significant at the 99% confidence against test data. The results showed that the gelation time was dependent more on pH than salinity. For low pH, the gelation time increased with increasing of the salinity, while for a high pH (>4) the relationship was inversed. The research shows that CCD can effectively be applied for the modeling of gelation time and finding an optimum condition to achieve maximum or minimum gelation time for different salinity and pH factors.     

Add/drop filter using in-plane slanted gratings in azo polymers

We have fabricated in-plane slanted gratings on azo-functionalized polymeric films using a fast, direct-writing method. By properly adjusting the resonance, these gratings can be used as 90 degrees integrated reflectors and add/drop filters in the plane of the film. We have produced an attenuation of 14.8 dB at 1560.2 nm with a FWHM of 6.47 nm. Also, a signal of 1548 nm wavelength was added to the output from a different direction. Any light shifted from the resonance will pass through the filter undisturbed.     

Evaluation of single virus detection through optical biosensor based on microsphere resonator

Shift of resonance frequency in microsphere optical resonator due to attachment of a desirable particle is obtained. Our 3-D finite element numerical method (FEM) simulations’ results show the path of light through microsphere and its variation due to attachment of particle. It is apparent that after attachment of particle to microsphere's surface, light is inclined to pass through the particle. Subsequently, the path of light becomes longer than previous. Because of this phenomenon, the resonance wavelength shifts to longer wavelengths. It is shown that microsphere optical resonator is a prominent biosensor for single virus detection since we applied characteristics of virus for particle in our simulations. Response of this biosensor depends on the characteristics of particle like its radius as we show in this article. Transmission spectrum of fiber which reveals a selected resonance frequency, have been studied in the frequency range of 106.3 to 107 THz under three different sizes of particles. The results show that the amount of frequency shift rises by enhancement of particle's size.     

Rheological and transport properties of sulfonated polyacrylamide hydrogels for water shutoff in porous media

In this research, an optimal hydrogel, based on sulfonated polyacrylamide, was synthesized by statistical design of experiments using central composite method. This new hydrogel composed of sulfonated polyacrylamide (AN125VLM) and chromium triacetate as copolymer and crosslinker, respectively. The bottle and rheological tests were conducted to investigate the gelation time, thermal stability, gel strength and also ultimate elastic modulus, complex modulus, and yield stress. It was found that copolymer concentration had the main effect in both rheological and transport properties of hydrogels. The sample prepared at optimum condition, i.e. copolymer concentration of 26,340 ppm and crosslinker/copolymer ratio of 0.12, had an ultimate elastic modulus of 29.9 kPa, yield stress of 800 Pa, and complex modulus of 32 kPa. A coreflooding test through fracture was carried out to examine the optimum gel performance in a porous media. A value of 483 for the residual resistance factor ratio of water to oil confirmed the high ability of the hydrogel in reducing the relative permeability of water to oil in fractured media. Copyright © 2014 John Wiley & Sons, Ltd.     

ENTROPY GENERATION ANALYSIS FOR A NON-AXISYMMETRIC FLOW OVER A ROTATING POROUS DISK

Journal of Applied Mechanics and Technical Physics - In the present study, entropy generation in a non-axisymmetric steady-state incompressible viscous flow over a single rotating porous disk is...     

Light extraction efficiency enhancement in organic light emitting diodes based on optimized multilayer structures

The main focus of this study is to improve the light extraction efficiency, as well as directionality of organic light emitting diodes (OLEDs) using multi-layer structures between Indium tin Oxide (ITO) and glass layers in a typical OLED. In conventional OLEDs, only about half of the light generated in the emission zone can reach to the glass substrate due to refractive index mismatch in ITO (n = 1.8?i0.01)/glass (n = 1.51) interface. The main attempt is to reduce the share of total internal reflection (TIR) and hence, the effect of different structures such as Thue-Morse and Fibonacci have been investigated and optimized with suitable layer thickness and materials based on Transfer Matrix Method (TMM). The most effective Multi-layer structures have been added to conventional OLED and have been analyzed the extraction efficiency using Finite Difference Time Domain (FDTD) method. Results show large enhancement of extraction efficiency (about 40%) in ITO/glass interface. Using this idea and applying micro-lenses array to glass substrate at the same time, one can get even higher extraction efficiency in OLED. The interesting aspect of this project is its easy fabrication process in order to commercialize the product with highest extraction efficiency and low fabrication cost.     

Effect of Nanoclay along with Other Effective Parameters on Gelation Time of Hydro Polymer Gels

In this work, a hydrogel was prepared by crosslinking of aqueous solutions of sulfonated polyacrylamide/chromium triacetate for the purpose of water shut-off treatment in oil fields. In order to screen the factors that affect the gelation time and investigate their interactions, a 32 run fractional factorial design was used in experimentation with eight factors (pH, CaCl₂ concentration, crosslinker/copolymer ratio, NaCl concentration, copolymer concentration and presence or absence of sodium lactate, nanoclay, and thiouria) and one response (gelation time). Furthermore, the analysis of variance (ANOVA) was implemented as a significant tool to evaluate the quality of the quadratic model. The ANOVA results of the developed model showed it was significant with a 99% confidence limit. Among the eight factors, presence of sodium lactate, copolymer concentration, presence of nanoclay, presence of thiouria, and crosslinker/copolymer ratio had, in order, the main effects, and the interactions between sodium lactate and crosslinker/copolymer ratio and between pH and crosslinker/copolymer ratio were highly significant.     

Linear frequency-doubling in dual Mid-IR-wavelength quantum cascade laser active region

In this paper we have proposed a novel quantum cascade laser active region design to obtain a dual-mid-IR-wavelength laser which is capable of frequency-doubling (13.77–6.88 μm) without utilizing nonlinear processes in two coupled shallow and deep quantum well structures. Optimized design of the active region leads to higher dipole matrix elements and thus higher laser performances. This method can be used to design laser structures with different frequency ratios.     

Highly enhanced second-order nonlinear susceptibilities in tailored GaN-AlGaN-AlN quantum well structures

A tailoring proposal for design of the strained quantum well structures, optimized with respect to the intersubband resonant second-order nonlinear properties, is presented in this article. A genetic-algorithm-based method is used in order to obtain the optimal potential shape, doping concentration and location in strained GaN-AlGaN-AlN quantum wells, and the structures are analyzed by a numerical solution of the Schrödinger-Poisson self-consistent method. In general form two types of asymmetric structures with remarkable results are obtained with different resonant frequencies, and in both cases results show a considerably high enhancement in the magnitude of the second-order nonlinear susceptibilities in higher resonant frequencies in comparison with a single quantum well structure with the same well width (5.02×10⁻⁸ m/V at to 2.9×10⁻⁵ m/V at and 2.43×10⁻⁵ m/V at ). The optimized structures exhibit considerable absorption coefficient and electroabsorption properties due to high dipole transition matrix element, high dopant concentration and reasonable Fermi level.