Kinetics of adsorption of methylene blue and rhodamine 6G on acrylic acid‐based superabsorbents

Superabsorbent polymers (SAPs) of acrylic acid, sodium acrylate, and acrylamide (AM), crosslinked with ethylene glycol dimethacrylate, were synthesized by inverse suspension polymerization. The equilibrium swelling capacities of the SAPs were determined and these decreased with increasing AM content. The adsorption of the two cationic dyes, methylene blue and rhodamine 6G, on the dry as well as equilibrium swollen SAPs was investigated. The amount of the dye adsorbed at equilibrium per unit weight of the SAPs and the rate constants of adsorption were determined. The amount of the dye adsorbed at equilibrium by the SAPs decreased with increasing mol % of AM in the SAPs. The amount of the dye adsorbed at equilibrium was almost equal for the dry and equilibrium swollen SAPs. However, the equilibrium swollen SAPs adsorbed dyes at a higher rate than the dry SAPs. The higher rate of adsorption was attributed to the availability of all the anionic groups present in the fully elongated conformation of the SAPs in the equilibrium swollen state. The effect of initial dye concentration on the adsorption was also investigated and the adsorption was described by Langmuir adsorption isotherms. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Adsorption of cationic dyes on poly(acrylic acid‐co‐sodium acrylate‐co‐acrylamide) superabsorbents

Inverse suspension polymerization was carried out to synthesize poly(acrylic acid‐co‐sodium acrylate‐co‐acrylamide) superabsorbent polymers (SAPs) crosslinked with ethylene glycol dimethacrylate (EGDMA). The equilibrium swelling capacities of the SAPs, determined by swelling them in DI water, were found to vary with the acrylamide (AM) content. The SAPs were used to adsorb four cationic dyes (Acriflavine, Auramine‐O, Azure‐I and Pyronin‐Y). The effect of AM content in the SAPs on the adsorption of the cationic dyes was investigated. Different initial concentrations of Azure‐I were used with the same amount of the SAP to explore the effect of initial dye concentration on the adsorption. The effect of the adsorbent amount was investigated by taking different amounts of SAP with a fixed initial concentration of Acriflavine. The kinetics of the dye adsorption was modeled by a first order model and the equilibrium amount of the dye adsorbed, adsorption rate coefficients, removal efficiency and partition coefficients were determined. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Electroviscous effects in a Carreau liquid flowing through a cylindrical microfluidic contraction

Electroviscous effects in steady, pressure-driven flow of a Carreau shear-thinning liquid in a cylindrical microfluidic 4:1:4 contraction–expansion at low Reynolds number are investigated numerically by solving the equations governing the flow, the electric field, and ion transport, using a finite volume method. The channel wall is considered to have a uniform surface charge density and the liquid is assumed to be a symmetric 1:1 electrolyte solution. Predictions are presented for a range of values of the shear-thinning parameters in the Carreau model for various surface charge densities and Debye lengths. The apparent/physical viscosity ratio is shown to increase as the degree of shear-thinning increases. Thus the electroviscous effect is stronger in shear-thinning liquids than it is when the liquid is Newtonian, a result previously obtained for uniform pipe flow of power-law liquids. The trend holds true regardless of the choice of surface charge density or Debye length, although the magnitude of the trend decreases as the surface charge density and/or the Debye length is reduced. Comparison between uniform pipe flow of a Carreau liquid and the corresponding power-law liquid that approximates it at large shear rates shows that the apparent/physical viscosity ratios for the two models are almost identical. A previous prediction that a near-wall region of reduced velocity can occur for pipe flow of a shear-thinning power-law liquid when EDLs are overlapping and surface charge density is elevated is confirmed for a Carreau liquid.     

Processing dependence of surface morphology in condensation cured PDMS nanocomposites

A processing method using high speed mixing was developed for the generation of nanocomposites comprised of α,ω-dihydroxy-polydimethylsiloxane (PDMS) and untreated fumed silica nanoparticles (U-FSN). Conventional condensation cure with poly(diethoxysiloxane) (PDES) was employed so as to generate PDMS/FSN nanocomposites with increasing weight fractions of siliceous domain. This study focuses on the changes in surface morphology imaged by non-contact or tapping mode AFM (TM-AFM) as a function of increasing the initial concentration of PDES. The ratios (X) of Si-OEt from PDES to Si-OH from PDMS end groups are 4X, 14X, 28X, 35X, 45X and 60X. Compared to prior work, two important differences in the present investigation are (1) the use of a high shear mixer as a processing tool to facilitate nanoparticle dispersion and (2) spin coating instead of dip coating. Common to the present and prior work is the use of TM-AFM for investigating surface morphology as a function of siliceous phase precursor concentration. TM-AFM phase images show nanoparticles are “reporters” and reflect effects of composition and processing on surface morphology. Near-surface nanoparticles are clearly imaged up to 35X, “disappear” at 45X, then “reappear” at 60X. These results are different from those previously reported where “disappearance” was noted for 14X compositions. The differing results reveal that processing conditions have an important effect on surface morphology. A model is presented that accounts for the surface morphological observations and wetting behavior via sessile drop measurements.     

Effect of hydrophilic poly(ethylene glycol) methyl ether additive on the structure,morphology, and performance of polysulfone flat sheet ultrafiltration membrane

In this work, effects of hydrophilic poly(ethylene glycol) methyl ether (PEGME) 5000 additive on the structure, morphology, and performance of polysulfone (PSF) membrane have been investigated. The membranes are prepared with direct blending of PEGME5000 (0–9 wt %) with two compositions of PSF (12 and 15 wt %) into N-methyl-2-pyrrolidone and further characterized in terms of morphology, structure, fouling, and ultrafiltration performance. The ternary phase diagram is plotted to investigate the thermodynamic stability of the system. Moreover, protein adsorption tests are conducted using bovine serum albumin (BSA) to see the effect of PEGME5000 on surface hydrophilicity. The ultrafiltration experiments are performed using humic acid (HA) solution and oil-in-water (o/w) emulsion. The result showed that, the contact angle decreased from 64° to 46° and from 67.6° to 49° for 12M and 15M membranes, respectively, indicating an improved hydrophilicity. The 12M and 15M membranes with 9 wt % of PEGME5000 have the lowest BSA adsorption due to highest antifouling property. The maximum permeability was obtained 0.72 and 0.51 L/m² h kPa for 12M5 and 15M3, respectively, due to maximum porosity which is also supported by the morphological result. In HA permeation, 12M5 and 15M3 achieved a maximum Flux _RR around 0.95 and 0.91, respectively, which was remarkably higher compared to 0.61 and 0.62 Flux _RR of 12M0 and 15M0. Also, PEGME5000 significantly affected the structure and morphology of the membranes. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47163.     

Regulation of DNA-dependent protein kinase by the Lyn tyrosine kinase

The Src-like protein-tyrosine kinase Lyn is activated by ionizing radiation and certain other DNA-damaging agents, whereas the DNA-dependent protein kinase (DNA-PK), consisting of the catalytic subunits (DNA-PKcs) and Ku DNA-binding components, requires DNA double-stranded breaks for activation. Here we demonstrate that Lyn associates constitutively with DNA-PKcs. The SH3 domain of Lyn interacts directly with DNA-PKcs near a leucine zipper homology domain. We also show that Lyn phosphorylates DNA-PKcs but not Ku in vitro. The interaction between Lyn and DNA-PKcs inhibits DNA-PKcs activity and the ability of DNA-PKcs to form a complex with Ku/DNA. These results support the hypothesis that there are functional interactions between Lyn and DNA-PKcs in the response to DNA damage.     

Convective Drying Kinetics of Red Chillies

The drying kinetics of four varieties of chillies (Pb-Lal, Pb-Guchhedar, Pb-Surkh, and CH-1) was studied. The chillies (pricked and unpricked) were pretreated in the dip sol solution. The treated chillies were dried in an automatic weighing experimental dryer at selected temperatures (45°, 50°, 55°, 60°, and 65°C). The results indicated that drying took place in the falling rate period. Out of three models considered, Page's model was found to be the most suitable for describing the drying behavior of chillies. The dependence of drying constant on temperature was analyzed using an Arrhenius equation. The variety Pb-Lal has the maximum value of activation energy (42.59 kJ/mol), which is also reflected in the reduced drying time for this variety. The results of quality studies of dried chillies in terms of capsaicin content and coloring matter indicated that the Pb-Lal variety had acceptable capsaicin content of 532.08 µg and coloring matter of 73.8 ASTA.     

Ultrahigh field induced strain and polarization response in electron irradiated poly(vinylidene fluoride-trifluoroethylene) copolymer

 The influence of electron dosage on the field induced strain, dielectric constant, and polarization response has been investigated in electron irradiated poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) 50/50 copolymer. It was found that under suitable electron dosage an ultrahigh electrostrictive strain can be achieved. Interestingly, material after irradiation exhibits many features resembling those of relaxor ferroelectrics, suggesting that the electron irradiation breaks up the coherent polarization domain in normal ferroelectric P(VDF-TrFE) copolymer into nano-polar regions that transform the material into a relaxor ferroelectric. In addition, many of the material properties including the field induced polarization, the electrostrictive strain, and elastic modulus exhibit irregular change (non-monotonical) with electron dosage, indicating a complex relation among the crosslinking density, crystallinity, crystallite size, and molecular conformation in determining the material responses. Received: 10 June 1998 / Accepted: 30 July 1998