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.     

Cu-based atom transfer radical polymerization of methyl methacrylate using a novel tridentate ligand with mixed donor atoms

This study is aimed at atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) using a novel catalyst. The bis-(2-dodecylsulfanyl-ethyl)-amine (SNS) tridentate ligand with mixed donor atoms was synthesized in high purity using inexpensive reagents and was reacted with copper(I) bromide to produce the CuBr/SNS catalyst. The catalyst mediated living polymerization of MMA yielding polymers with controlled molecular masses and narrow molecular mass distributions (PDI < 1.25). Also, the kinetic plot exhibited a linear increase of ln([M]₀/[M]) versus time, indicating constant concentration of propagating radicals during the polymerization. The products were characterized by ¹H NMR, ¹³C NMR, FT-IR, UV-VIS, GC and elemental analyses (CHNS) and by GPC.     

Fundamentals and some applications of photoelectrocatalysis and effective factors on its efficiency: a review

Effluents of a large variety of industries usually contain important quantities of synthetic organic compounds. The discharge of these compounds in the environment causes considerable non-aesthetic pollution and serious health risk factors. Since conventional wastewater treatment plants cannot degrade the majority of these pollutants, powerful methods for the decontamination of dye wastewaters have received increasing attention over the past decade. In this work, fundamentals and main applications of photoelectrocatalysis as one of the most powerful and recent progresses of emerging photoassisted electrochemical treatments with UV irradiation are studied. The effect of various effective factors such as photoanode type, light source and its intensity, pH solution value, type and concentration of supporting electrolyte, type of cathode electrode, to be moving of photoanode or solution, thicknesses of semiconductor film on the electrode surface, and applied potential on the destruction of pollutants is described. Furthermore, various methods used for TiO₂ modification are mentioned. Also, application of photocatalysts except semiconductors is presented for photoelectrocatalytic aims. Finally, application of photoelectrocatalysis in determination of materials as a new method is discussed.     

Numerical study of induction heating in melt growth systems—Frequency selection

A set of 2D finite element numerical simulation of induction heating process for an oxide Czochralski crystal growth system has been made for a range of f=1–100 kHz applied frequency of driving current. It was shown that the frequency selection has a marked effect in all basic induction phenomena, including electromagnetic field distribution, skin depth, coil efficiency, and intensity and structure of heating in the growth setup.     

Nonlinear dynamics of a flexible rotor on tilting pad journal bearings experiencing rub–impact

Nonlinear Dynamics - Rub–impact phenomenon occurring in hydrodynamic journal bearings is one of the main malfunctions in rotating machines and causes undesirable dynamic behavior. In order to...     

Silver nanoparticles supported on ionic‐tagged magnetic hydroxyapatite as a highly efficient and reusable nanocatalyst for hydrogenation of nitroarenes in water

A novel chemically modified magnetic hydroxyapatite (MHAp) was prepared and used as support and stabilizer for the synthesis of silver nanoparticles. First, 1,4‐diazabicyclo[2.2.2]octane (DABCO) was successfully grafted onto the surface of MHAp, and then silver nanoparticles were homogeneously loaded on mesoporous MHAp‐DABCO (ionic‐tagged MHAp) nanocomposite by in situ chemical reduction of silver nitrate using sodium borohydride. The structure and properties of the resulting MHAp‐DABCO‐Ag nanocomposite were confirmed using various techniques. The catalytic activity of ionic‐tagged MHAp‐Ag nanocatalyst was investigated for the hydrogenation reaction of nitroarenes in aqueous media. The results reveal that the Ag‐containing inorganic–organic nanocomposite is highly efficient for the reduction of a wide range of aromatic nitro compounds under green conditions. The superparamagnetic nature of the nanocatalyst leads to its being readily removed from solution via application of a magnetic field, and it can be easily stored and reused.     

Graphs With Few Matching Roots

We determine all graphs whose matching polynomials have at most five distinct zeros. As a consequence, we find new families of graphs which are determined by their matching polynomials.     

Existence of solutions in variational relation problems without convexity

Two main existence conditions for solutions of variational relation problems are established without convexity. The first one is based on a finite solvability property and the second one on generalized KKM mappings. These conditions unify and strengthen several existing results in the literature on the topic. A model of satisficing process by rejection is considered which gives an economic interpretation of the introduced concepts.     

Matrix Heterogeneity Effects on Gas Transport and Adsorption in Coalbed and Shale Gas Reservoirs

In coalbeds and shales, gas transport and storage are important for accurate prediction of production rates and for the consideration of subsurface greenhouse gas sequestration. They involve coupled fluid phenomena in porous medium including viscous flow, diffusive transport, and adsorption. Standard approach to describe gas–matrix interactions is deterministic and neglects the effects of local spatial heterogeneities in porosity and material content of the matrix. In this study, adopting weak-noise and mean-field approximations and using a statistical approach in spectral domain, matrix heterogeneity effects are investigated in the presence of non-equilibrium adsorption with random partition coefficient. It is found that the local heterogeneities can generate non-trivial transport and kinetic effects which retard gas release from the matrix and influence the ultimate gas recovery adversely. Macro-transport shows 1/[1 + N _Pe /(1 + N _Pe )] dependence on the Péclet number, and persists at the diffusive ultra-low permeability limit. Macro-kinetics is directly related to Thiele modulus by the following expression: N _Th /(1 + 2N _Pe ). It leads to trapping of gas in the adsorbed phase during its release from the matrix, and to an adsorption threshold during the gas uptake by the matrix. Both effects are proportional to the initially available adsorbed gas amount and becomes more pronounced with the increasing variance of the porosity field. Consequently, a new upscaled deterministic gas mass balance is proposed for practical purposes. Numerical results are presented showing free and adsorbed gas distributions and fractional gas sorption curves for unipore coal matrix exhibiting Gaussian porosity distribution. This study is a unique approach for our further understanding of the coalbeds and gas shales, and it is important for the development of sound numerical gas production and sequestration models.