Presence Of Polyacrylate Research Articles

Radiation-Induced Synthesis and Superparamagnetic Properties of Ferrite Fe3O4 Nanoparticles.

Ultra-small magnetic Fe3O4 nanoparticles are successfully synthesized in basic solutions by using the radiolytic method of the partial reduction in FeIII in the presence of poly-acrylate (PA), or by using the coprecipitation method of FeIII and FeII salts in the presence of PA. The optical, structural, and magnetic properties of the nanoparticles were examined using UV-Vis absorption spectroscopy, high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and SQUID magnetization measurements. The HRTEM and XRD analysis confirmed the formation of ultra-small magnetite nanoparticles in a spinel structure, with a smaller size for radiation-induced particles coated by PA (5.2 nm) than for coprecipitated PA-coated nanoparticles (11 nm). From magnetization measurements, it is shown that the nanoparticles are superparamagnetic at room temperature. The magnetization saturation value Ms = 50.1 A m2 kg-1 of radiation-induced nanoparticles at 60 kGy is higher than Ms = 18.2 A m2 kg-1 for coprecipitated nanoparticles. Both values are compared with nanoparticles coated with other stabilizers in the literature.

Understanding the stability mechanism of silica nanoparticles: The effect of cations and EOR chemicals

We have investigated the conditions of colloidal stability of silica nanoparticles smaller than 100 nm for their applications in enhanced oil recovery (EOR), especially pertaining to chemical flooding processes. Using zeta sizer and dynamic light scattering techniques, the stability of silica nanoparticle (SNP) dispersions has been investigated by variation of the pH, composition of salt solutions, addition of surfactants and polyelectrolytes. Such conditions can be encountered in oil reservoirs. It was found that changing pH from 5 to 10 had a negligible effect on the size of SNPs, whereas its zeta potential increased with increasing pH. Aggregation of SNPs is a partially reversible process for low degrees of aggregation in 500 mM NaCl, whereas observed strong aggregation in 1000 mM NaCl was irreversible. A critical aggregation concentration (CAC) was defined for the different salts investigated, above which the SNP dispersion became unstable at a fixed pH of 9.5. The CAC for NaCl was approximately 200 times higher than for CaCl2 and MgCl2. Our observations could not be explained completely by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Therefore, we have included non-DLVO interactions such as cation bridging, hydration forces, and steric effects. The additional presence of anionic alcohol alkoxy sulfate (AAS) surfactant slightly destabilized the SNP solution, but by the addition of polyacrylate (PA) was effectively stabilized. With increasing PA concentration, the CAC for both CaCl2 and MgCl2 increased. Upon addition of 100 ppm PA, the CAC increased by a factor of five compared to the situation in the absence of PA. Reducing the solution pH below 8.5, SNP can be stabilized in higher salinity in the presence of PA. The obtained results contribute to a better fundamental understanding of the SNP stability mechanism and a guide to optimize the SNP injection process with EOR chemicals.

Layered double hydroxide nanoparticles customization by polyelectrolyte adsorption: mechanism and effect on particle aggregation

Adsorption of polyelectrolytes (PEs) is a common strategy for stabilizing nanoparticles and customizing their properties. Although scarcely explored for layered double hydroxide nanoparticles (LDH-NPs), it can be used to increase their functionality in pharmaceutical and biomedical applications, among others. In this work, LDH-NPs intercalated with chloride, ibuprofen and ketoprofen were synthesized and modified with carboxylate containing PEs with different structures and physicochemical properties. The PEs adsorption mechanism on LDH-NPs and its effect on the aggregation of the obtained hybrids were studied by zeta potential and hydrodynamic diameter determinations on chloride intercalated LDH-NPs dispersions in the presence of polyacrylate (PA) at different concentrations. PA adsorption behavior was compared to that of citrate anion to contrast the adsorption mechanism of PEs and anions. Afterwards, the study was extended to other PEs (alginate and carbomer) as well as to drug intercalated LDH-NPs. PA adsorbed at the surface of LDH-NPs with high affinity: at low concentrations, PA was irreversibly adsorbed due to the positive structural charge of LDH-NPs and the flexible and negatively charged structure of PA. This high affinity caused a particle charge inversion, which results in negatively charged LDH-NPs stabilized by both electrostatic interactions and steric hindrance. Due to their structure, alginate and carbomer showed a lower affinity and, consequently, a lower capacity to produce LDH-NPs disaggregation. Finally, PEs adsorption allowed enhancing the disaggregation and modifying the interfacial properties of both ibuprofen and ketoprofen intercalated LDH-NPs producing only a small release of the drug loading.

The formation and catalytic activity of silver nanoparticles in aqueous polyacrylate solutions

Silver nanoparticles (AgNPs) have been synthesized in the presence of polyacrylate through the reduction of silver nitrate by sodium borohydride in aqueous solution. The AgNO3 and polyacrylate carboxylate group concentrations were kept constant at 2.0 × 10–4 and 1.0 × 10–2 mol·L–1, respectively, while the ratio of [NaBH4]/[AgNO3] was varied from 1 to 100. The ultraviolet-visible plasmon resonance spectra of these solutions were found to vary with time prior to stabilizing after 27 d, consistent with changes of AgNP size and distribution within the polyacrylate ensemble occurring. These observations, together with transmission electron microscopic results, show this rearrangement to be greatest among the samples at the lower ratios of [NaBH4]/[AgNO3] used in the preparation, whereas those at the higher ratios showed a more even distribution of smaller AgNP. All ten of the AgNP samples, upon a one thousand-fold dilution, catalyze the reduction of 4-nitrophenol to 4-aminophenol in the temperature range 283.2–303.2 K with a substantial induction time being observed at the lower temperatures.

Transport Studies of Divalent Ions through Nafion-117 Ion Exchange Membrane in the Presence of Polyacrylate

The effect of binding of divalent ions (Mg2+ and Ba2+) with a polyacrylate anion on the Donnan membrane equilibrium distribution and the transport kinetics have been studied using Nafion-117 membrane. The extent of association of the divalent counterions with polyacrylate has been ascertained from the deviation from Donnan membrane equilibrium condition. The equilibrium concentrations of ions in polyacrylate compartment have been found to be in excess of expected equilibrium concentrations obtained from Donnan membrane equilibrium condition. This has been attributed to higher electrostatic interactions of divalent ions with the polyacrylate backbone compared to the monovalent ions. The strength of binding has been found to depend on the nature of divalent ion. Precipitation has been observed for Ba2+, thereby changing the total salt concentration of the polyacrylate compartment. Also, the strength of counterion binding has been found to depend on salt concentrations of the two compartments. The rate of transport of the ions with polyacrylate in the receiver solution has been calculated based on modified Nernst–Planck (NP) approach. The calculated transport kinetics have been found to agree with the experimental transport kinetics.

Transport Studies of Monovalent Ions through Nafion-117 Ion Exchange Membrane in Presence of Polyacrylate

The results of equilibrium distribution and transport kinetics of monovalent (Li+, Na+, and Cs+) ions through Nafion-117 ion exchange membrane in presence of polyacrylate anion have been presented. For Na+-Li+ system, equilibrium distributions in the presence and absence of polyacrylate have been found to be the same indicating that the Donnan membrane equilibrium is not affected by the presence of polyacrylate. For the Na+-Cs+ system, a favored transport of Cs+ ion to the polyacrylate compartment has been observed, indicating the binding of Cs+ ion with polyacrylate is stronger than other monovalent ions. This is due to the lower hydration radius of Cs+ ions. The deviation from Donnan membrane equilibrium condition has been used to obtain information about the fraction of counter-ions bound to the polyacrylate. The transport profile in the presence of polyacrylate has also been calculated based on the modified Nernst Planck (NP) approach, taking into account the fraction of counter-ions bound to the polyacrylate ion. The Donnan relation has been used to obtain the concentration of ions at the solution/membrane interface. The self-diffusion coefficients of ions and membrane ion exchange capacity have been given as input parameters in the calculations. The calculated time profile has been found to agree well with the experimental time profile.

Radiation-induced pink nickel oligomeric clusters in water. Pulse radiolysis study.

γ-rays and pulse radiolysis of aqueous solutions of Ni(2+) ions in the presence of polyacrylate (PA(-)) and 2-propanol leads to the formation of metastable species absorbing at 540 nm that are ascribed to "pink" oligomeric clusters of a few nickel atoms only. The molar absorption coefficient is evaluated as ε540 nm = 3300 ± 300 L mol(-1) cm(-1) per Ni(0) atom. The successive steps from the reduction of Ni(2+) into Ni(+) ions to the formation of the pink clusters at 540 nm under conditions of complexation by PA(-) are investigated by pulse radiolysis. The yield of the formation of pink clusters increases markedly with the irradiation dose rate, demonstrating the occurrence of the disproportionation of the [Ni(+), PA(-)] complex after a single electron pulse. The reduction and nucleation mechanisms, including rate constants, in competition with the back oxidation by protons, particularly at low dose rate, are discussed.

Induced organic fouling with antiscalants in seawater desalination

The effect of exposure reverse osmosis (RO) membrane to antiscalants (AS) on consequent organic fouling during seawater desalination was analyzed. Membrane surface properties (hydrophobicity and zeta potential) were altered upon the conditioning of the membrane with AS during the desalination process. For all AS used, polyphosphonate, polyacrylate, or dendrimeric carboxylated based AS, membrane zeta-potential became less negatively charged over pH range between 3 and 10. Furthermore, the membrane became significantly more hydrophobic when dendrimeric carboxylated and polyacrylate based AS were used and only minor effects were observed for the polyphosphonate based AS. The membrane organic fouling process, tested with different model organic foulants (alginate and BSA), was significantly enhanced in the presence of polyacrylate or carboxylated dendrimeric based AS, which were used to condition the membrane surface. These changes in fouling behavior are likely attributed to the AS effects on RO membrane hydrophobicity and zeta potential after exposure and adsorption to the RO membrane. Force curve measurements using atomic force microscopy (AFM) on membranes and adsorption of the organic foulants on sensors of quartz crystal microbalance with dissipation (QCM-D) monitoring were used to explain the induced adsorption of the model organic foulants by polyacrylate and carboxylated dendrimeric based AS.

Poly(acrylate‐b‐styrene‐b‐isobutylene‐b‐styrene‐b‐acrylate) Block Copolymers via Carbocationic and Atom Transfer Radical Polymerizations

A series of polyacrylate‐polystyrene‐polyisobutylene‐polystyrene‐polyacrylate (X‐PS‐PIB‐PS‐X) pentablock terpolymers (X=poly(methyl acrylate) (PMA), poly(butyl acrylate) (PBA), or poly(methyl methacrylate) (PMMA)) was prepared from poly (styrene‐b‐isobutylene‐b‐styrene) (PS‐PIB‐PS) block copolymers (BCPs) using either a Cu(I)Cl/1,1,4,7,7‐pentamethyldiethylenetriamine (PMDETA) or Cu(I)Cl/tris[2‐(dimethylamino)ethyl]amine (Me6TREN) catalyst system. The PS‐PIB‐PS BCPs were prepared by quasiliving carbocationic polymerization of isobutylene using a difunctional initiator, followed by the sequential addition of styrene, and were used as macroinitiators for the atom transfer radical polymerization (ATRP) of methyl acrylate (MA), n‐butyl acrylate (BA), or methyl methacrylate (MMA). The ATRP of MA and BA proceeded in a controlled fashion using either a Cu(I)Cl/PMDETA or Cu(I)Cl/Me6TREN catalyst system, as evidenced by a linear increase in molecular weight with conversion and low PDIs. The polymerization of MMA was less controlled. 1H‐NMR spectroscopy was used to elucidate pentablock copolymer structure and composition. The thermal stabilities of the pentablock copolymers were slightly less than the PS‐PIB‐PS macroinitiators due to the presence of polyacrylate or polymethacrylate outer block segments. DSC analysis of the pentablock copolymers showed a plurality of glass transition temperatures, indicating a phase separated material.

Self-Assembly of Polyacrylate-Capped Platinum Nanoparticles on a Polyelectrolyte Surface: Kinetics of Adsorption and Effect of Ionic Strength and Deposition Protocol

Polyacrylate-capped Pt nanocrystallites of 2.5 ± 0.6 nm diameter were synthesized by reduction of Pt(IV) with citrate in the presence of polyacrylate and were self-assembled layer-by-layer in poly(diallyldimethylammonium chloride) by virtue of the Coulombic attraction between the negatively charged capping agent and the cationic polyelectrolyte. The self-assembly protocol resulted in a reproducible consecutive surface-charge buildup, leading to a linear incorporation of nano-Pt per layer. TEM imaging revealed a chainlike distribution of the nanoparticles on the polymer surface at submonolayer coverage. The density of assembled nanoparticles per layer can be controlled by varying the dipping time, the Pt solution ionic strength, and its composition or by resorting to an interrupted-deposition protocol involving multiple rinsing/drying cycles per layer. The dynamics of nano-Pt assembly on PDDA was followed ex-situ by UV−visible spectroscopy. The adsorption was found to take place via two kinetics regimes at different time scales. Initially, the adsorption rate is believed to be limited by the nanoparticles availability at the solution/surface interface. At high surface coverage, the slower polyelectrolyte−nanoparticle surface rearrangement necessary for further attachment becomes the rate-determining step, leading to a pseudosaturation within ∼1 h.

Chitosan-based hydrogels: synthesis and characterization.

Chitosan (CHI) is a polysaccharide of beta-1,4-linked 2-amino-2-deoxy-D-glucopyranose derived by N-deacetylation of chitin in aqueous alkaline medium. The shells of crustaceans such as crabs, shrimp, and lobster are the current source of chitosan. It is known to be non-toxic, odourless, biocompatible in animal tissues and enzymatically biodegradable. For these reasons much research interest has been paid to its biomedical, ecological, and industrial applications over the past decade. However, its rigid crystalline structure, poor solubility in organic solvents and poor processability have limited its use. To broadening its range of applications, a growth research effort has been devoted to explore ways of modifying Chitosan. Here it has been reported on the synthesis of new hydrogels, obtained by self-curing chitosan with acrylic acid (AA) and methyl acrylate (MA). The hydrogels were characterized by FTIR, swelling and rheological analysis. The results of this study showed that the swelling and mechanical properties of chitosan are highly improved by the presence of poly acrylate. The swelling degree of these materials does not depend upon the ratio MA/AA. It is possible to improve and modulate the mechanical properties of the hydrogels by changing the relative MA/AA ratio.

The nature of colloidal platinum in aqueous solution: features of catalytic reactions

The specific features of the catalytic reduction of methylviologen by dihydrogen in water in the presence of platinum colloids synthesized by various methods are studied. The colloids prepared by the radiation-chemical reduction of PtCl42– in the presence of polyacrylate or polyphosphate as stabilizers and colloids prepared by the reduction with dihydrogen efficiently catalyze the reaction. The “citrate” colloids synthesized by the reduction of PtCl62– with citric acid are characterized by a prolonged induction period after which these colloids also gain the catalytic activity. We assume that the “citrate” platinum colloids are giant clusters with the close-packed metal core containing the “magic” number of platinum atoms (Pt561), which are coordinated by the ligand molecules blocking the surface of the metal particle. In the presence of H2, the ligand molecules are decomposed or removed from the surface, which is accompanied by the appearance of the catalytic activity.

Thermodynamic analysis for the interaction of polyacrylate with wax in heptane

The effect of polyacrylate (PA) on wax-precipitation temperature in heptane was investigated using differential scanning calorimetry (DSC). A thermodynamic analysis for the dissolution of wax in the absence and presence of PA was conducted. Results suggested that the change in wax-precipitation temperature caused by the introduction of the additives may be regarded as an index for characterizing the interaction of polymer additives with wax.

Radiation-chemical reduction of CO2+ ions in aqueous solution. Metal sols and their properties

The radiation-chemical reduction of Co2+ ions in an aqueous solution of Co(ClO4)2 containing sodium formate was studied. Stable metal sols containing spherical particles with a diameter of 2–4 nm are formed under γ-irradiation in the presence of polyacrylate as the stabilizing additive. An aqueous solution of colloidal cobalt has an optical absorption that increrases smoothly in the UV region without a maximum to 200 nm (ɛ200=1.3·104 mol-1 L cm-1). It is established that the radiation-chemical reduction of the Co2+ ions occursvia an autocatalytic mechanism. The metal sols catalyze the reduction of the Co2+ ions by Co2 − radical ions formed under irradiation. The properties of the sols were studied, and it is shown that they are readily oxidized by hydrogen peroxide and other oxidants. The mechanism of chemical reactions involving the sols is discussed.

The adsorption of starch derivatives onto kaolin

Modified starches are widely used as binders and thickening agents in paper coating formulations. Frequently, kaolin is used as the coating pigment. In this work, the adsorption of modified starches onto kaolin has been studied. Adsorption behaviour was found to depend both upon the type of chemical modification and botanical orgin. With a phosphate ester of potato starch, adsorption was reduced in the presence of sodium polyacrylate used as a deflocculant on the clay. No fractionation of the starch components was observed during adsorption. These results imply an electrostatic mechanism of interaction with the edge aluminium sites. In contrast, a hydroxyethyl ether of corn (maize) starch showed preferential adsorption of amylose, which is shown to be a result of preferential etherification of this component with ethylene oxide. With this non-ionic derivative, adsorption was not reduced by the presence of polyacrylate. A mechanism of adsorption involving hydrogen bonding of hydroxyethyl groups to silanol or aluminol groups on the kaolin surface is proposed in this case. A hydroxyethyl ether of potato starch showed preferential adsorption of amylopectin, together with some sensitivity to polyacrylate. With potato starch, the adsorption behaviour is dominated by the presence of naturally occurring phosphate ester groups, which are associated with the amylopectin.

STM identification of silver oligomer clusters prepared by radiolysis in aqueous solution

Silver oligomers prepared by radiolysis in aqueous solution in the presence of polyacrylate and absorbing at ≈ 290 nm have been imaged by STM in air after being deposited on a HOPG surface. Clear images with atomic resolution are observed, showing flat clusters of 0.7 nm. Each cluster contains seven (or possibly eight) atoms corresponding to the stoichiometry (Ag 4+ m ) m+ , m = 3 (or 4), for the clusters in aqueous solution. No interference due to the polyanion (present in the solution as a stabilizing agent) is found for adsorbate densities.

Influence of natural and synthetic inhibitors on the crystallization of calcium oxalate hydrates

The kinetics of crystallization of calcium oxalate monohydrate was studied in the presence of polyacrylate, and the growth of both this salt and the trihydrate was investigated in the presence of polyasparatic acid, polyglutamic acid, and heparin. We monitored the crystallization reactions either by following the change in lattice-ion concentrations as a function of time or by maintaining constant supersaturation via the replacement of lattice ions during the experiments. In addition, the crystallization reactions of calcium oxalate monohydrate, dihydrate, and trihydrate were studied in the presence of urine fractions (5%, v/v) separated by molecular weight in the range of 1 000–50 000 Da from whole urine.

Reduction of Ag+ in Aqueous Polyanion Solution: Some Properties and Reactions of Long‐Lived Oligomeric Silver Clusters and Metallic Silver Particles

AbstractRadiolytic reduction of AgClO4 solutions containing a polyanion leads to the formation of long‐lived oligomeric silver clusters which are stabilized on the polymer chains. Under suitable conditions, the accompanying formation of colloidal silver consisting of metallic particles is strongly suppressed and cluster concentrations of several 10−4 M can be produced. In the presence of polyacrylate, the clusters are particularly long‐lived; they have absorption bands at 300 nm, 340 nm, and 370 nm. The bands of the latter two clusters are red‐shifted as compared to the bands of the unstabilized clusters or clusters stabilized by polyphosphate. The Ag24+ cluster, which is formed in the initial stages of Ag+ reduction, absorbs at 275 and 480 nm in the presence of polyacrylate. – The various clusters react at different rates with electron acceptors, such as oxygen, carbon tetrachloride and nitromethane. The clusters also react with complexing agents, such as ammonia, cyanide and hydrogen sulfide anions, to form larger particles of silver and/or larger complexed clusters. The great reactivity of the clusters towards nucleophilic reagents is explained by the high coordinative unsaturation of the silver atoms in the clusters. This also explains the stabilization of the clusters by the anion groups of the polymers used. – These reactivity studies were also complemented by investigating the reactions of larger silver particles, which already have metallic properties, with complexing agents. The oxidative corrosion of such particles is strongly accelerated by the complexing agents. A mechanism for the catalysis of the oxidative corrosion is presented, in which the principle steps are the complexation of silver atoms on the surface with simultaneous electron transfer into the metal interior (“pre‐complexation” or “pre‐oxidation” of surface atoms) followed by pick‐up of the electrons by oxygen.