Synthesis and solution properties of poly(acrylamide-styrene) block copolymers with high hydrophobic content

Hydrophobically associating block copolymers of polyacrylamide/styrene with a high hydrophobe content were synthesized using micellar copolymerization under various conditions of surfactant and initiator concentrations with the objective of determining the conditions that produce optimum solution properties for enhanced oil recovery. Solubilities, aqueous solution viscosities and interfacial properties with air and oil of the copolymers were investigated. The influence of salt on the solution properties was also studied. Nature of hydrophobic sites and onset of hydrophobic association were studied by measuring the fluorescence of pyrene in polymer solutions. Optimum solution properties were obtained for copolymers synthesized under conditions of high surfactant and initiator concentrations. The copolymers displayed substantial thickening properties at low concentrations with enhanced thickening in the presence of salt. The interfacial tensions of the aqueous solutions with n-decane and air were also reduced. Interfacial properties were slightly sensitive to salt concentration. The copolymer solutions showed shear and temperature thinning behaviors typical of polymer solutions.     

Magneto-Caloric Effect in Ge0.95Mn0.05 Films

In this paper, a phenomenological model is used to calculate magneto-caloric properties of Ge_0.95Mn_0.05 films fabricated with substrate temperatures of 85, 100, and 120 ^°C. Calculations showed that the ferromagnetic Mn₅Ge₃ phase improves magneto-caloric properties of the Ge_0.95Mn_0.05 films. It is suggested that Ge_0.95Mn_0.05 films are suitable candidates as refrigerants near room-temperature region.     

Influence of Nonionic Rosin Surfactants on Surface Activity of Silica Particles and Stability of Oil in Water Emulsions

Rosin as a natural product has become a source for production of less toxic bio-surfactants to produce emulsions which are widely used in various agriculture and food products, cosmetic, and pharmaceutical industries. In this respect, a nonionic surfactant was prepared from reaction of rosin acids and rosin maleic anhydride adduct with poly(ethylene glycol) monomethyl ether 750 (MPEG 750) to produce a rosin ester (RMPEG 750). The surface activity parameters of the prepared surfactants, such as surface excess concentration (Γ _max), the area per molecule at interface (A _min), and the effectiveness of surface tension reduction, were measured to determine the micellization and adsorption characteristics of the prepared surfactants at the water/air interface. The adsorption of the prepared surfactants on the surface of either hydrophilic or hydrophobic silica particles was determined using a spectrophotometric method. Interfacial tension between water and toluene were measured to select the best condition to obtain toluene/water emulsion in the presence of modified solid silica particles. The effects of silica particle hydrophilicity and the surfactant concentrations on the surface, interfacial activity, and on the emulsion drop size were also investigated.     

Rheological and mechanical properties of poly(lactic acid)/polystyrene polymer blend

Properties modification by blending polymers has been an area of immense interest. In this work, rheological and mechanical properties of poly(lactic acid)/polystyrene (PLA/PS) blends were investigated. PLA/PS blends in different ratios were prepared using a laboratory scale single screw extruder to obtain (3 mm) granules. Rheological properties were studied using a capillary rheometer and the Bagley’s correction was performed. True shear rate (γ _r ), true shear stress (τ _r ), and true viscosity (η _r ) were determined, the relationship between true viscosity and (1/T) was studied for PLA70 blend and the flow activation energy at a constant shear stress (E _τ ) and a constant shear rate (E _γ ) was determined. The mechanical property measurements were performed at room temperature. Stress at break and strain at break were determined. The results showed that PLA/PS blend exhibited a typical shear-thinning behavior over the range of the studied shear rates, and the viscosity of the blend decreased with increasing PLA content. Also it was found that no equal-viscosity temperature exists between PLA and PS. The mechanical results showed immiscibility between PLA and PS in the blend.     

Structure–process–yield interrelations in nanocrystalline cellulose extraction

In order to improve the extraction of nanocrystalline cellulose (NCC) from sulfuric acid hydrolysis of chemical pulps, we have studied the effect of hydrolysis conditions on the degree of polymerization (DP), the extent of sulfation, morphological, and solid‐state characteristics of the extracted materials vis‐à‐vis yield. Our results demonstrate that sulfation plays a significant role in (i) determining the yield of, and (ii) imparting the unique solid‐state characteristics to, the extracted, H₂O‐insoluble cellulose nanomaterial from sulfuric acid hydrolysis. The hydrolysis process is itself proven to be highly reproducible, and NCC with high crystallinity (>80%) and a yield between 21% and 38% could be extracted from a fully bleached, commercial softwood kraft pulp using 64 wt.% sulfuric acid at 45–65°C after freeze drying. The NCC aggregates, with iridescent patterns typical of chiral nematic materials, are parallelepiped rod‐like structures which possess cross‐sections in the nanometer range and lengths orders of magnitude larger, resulting in high aspect ratios. The Ruland–Rietveld analysis was employed to precisely resolve X‐ray diffraction patterns and obtain information on crystallite size, crystalline and amorphous areas, and crystallinity of the extracted materials.     

Flavonols of lotus (<Emphasis Type="Italic">Nelumbo nucifera,</Emphasis> Gaertn.) seed epicarp and their antioxidant potential

Large amounts of fresh seed epicarp of Nelumbo nucifera Gaertn. (FSENN) are discarded in China without any utilization. The aim of this study was to identify the flavonols found in a fraction of an extract of FSENN, and to measure their levels and investigate antioxidant properties. Glycosylated flavonols in fraction 2 (Fr2) from the extract of FSENN and their aglycones were identified by HPLC-ESI–MS² (negative mode), and six glycosylated and one aglycone flavonols in Fr2 were found. We also quantified flavonol aglycones (myricetin, quercetin, kaempferol and isorhamnetin) using HPLC method. The result showed that the quercetin content (10.2 mg/g of dry fraction) was higher than that of other aglycones. Antioxidant properties of Fr2 were evaluated in vitro by a number of methods including 2, 2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging, the β-carotene bleaching method, and hydroxyl radical and hydrogen peroxide scavenging ability using the chemiluminescence method. This antioxidant potential in terms of IC₅₀ values was 5.48, 40 ± 0.14 and 0.62 ± 0.05 μg (dry Fr2)/mL on DPPH radicals, hydroxyl radicals and hydrogen peroxide, respectively. The Fr2 also exhibited antioxidant property in the β-carotene bleaching assay. In total, it possesses high levels of flavonol compounds with high antioxidant potential, and it is beneficial for the treatment or prevention of a variety of diseases and has nutraceutical potential.     

MHD flow over an inclined radiating plate with the temperature‐dependent thermal conductivity,variable reactive index,and heat generation

We study the effects of higher‐order chemical reaction and heat generation on coupled heat and mass transfer by MHD mixed convection from a permeable radiating inclined plate with the thermal convective boundary condition. The governing boundary layer equations are formulated and transformed into a set of similarity equations using dimensionless similarity variables developed by Lie group analysis. The resulting equations are then solved numerically using Maple 13 which uses a fourth–fifth order Runge–Kutta–Fehlberg algorithm for solving nonlinear boundary value problems. A representative set of numerical results are displayed graphically and discussed to show some interesting aspects of the parameters: convective heat transfer (γ), the angle of inclination (α), generation order of chemical reaction (n), reaction rate (λ), the Prandtl number (Pr), and the Schmidt number (Sc) on the dimensionless axial velocity, the temperature, and the concentration profiles. Also effects of pertinent parameters on the skin friction factor, the rate of heat, and the rate of mass transfer are obtained and displayed in tabular form. Good agreement is found between the numerical results of the present paper with the earlier published works under some special cases. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20409     

Investigation of combined heat and mass transfer by Lie group analysis with variable diffusivity taking into account hydrodynamic slip and thermal convective boundary conditions

The present paper investigates heat and mass transfer over a moving porous plate with hydrodynamic slip and thermal convective boundary conditions and concentration dependent diffusivity. The similarity representation of the system of partial differential equations of the problem is obtained through Lie group analysis. The resulting equations are solved numerically by Maple with Runge–Kutta–Fehlberg fourth–fifth order method. A representative set of results for the physical problem is displayed to illustrate the influence of parameters (velocity slip parameter, convective heat transfer parameter, concentration diffusivity parameter, Prandtl number and Schmidt number) on the dimensionless axial velocity, temperature and concentration field as well as the wall shear stress, the rate of heat transfer and the rate of mass transfer. The analytical solutions for velocity and temperature are obtained. Very good agreements are found between the analytical and numerical results of the present paper with published results.