Effect of pH on the Rheology of A1-Mg M iteed Meta1 Hydroxide——Montmorillonite Aqueous Suspension

The effects of the pHs of Mtsuspension(pH_Mt),AMH sol(pH_A)and mixedsuspension(pH_mix)on the rheology of mixed su sp en sion w ere studied.The mixed suspension consisted of the alum in ium magnesium mixed metal hydroxide(AM H) colloidal prt icles which possessed permanent positive charges and the Na-montmorillon ite(M t)particles which po ssessed permanent nega tive charges.The results showed that the pHs did not affect the Bingham yield poin t(YP)of the mixed suspen sionsin the various pHs(i.e.,pH_Mt,pH_A and pH_mix)range of 8—10 almost. When the pH values were above 10 the YPs increased ma rked ly w ith increa sing pH_Mt and pH_mix,but decreased sharply with increasing pH_A.The mechanisms of the effect of pH on the rheology of mixed suspensions were also investigated.     

Studies on Colloidal Properties of Mixed Metal Hydroxide－Clay Aqueous Suspension

ＳｔｕｄｉｅｓｏｎＣｏｌｌｏｉｄａｌＰｒｏｐｅｒｔｉｅｓｏｆＭｉｘｅｄＭｅｔａｌＨｙｄｒｏｘｉｄｅ－ＣｌａｙＡｑｕｅｏｕｓＳｕｓｐｅｎｓｉｏｎＮＯＵｗａｎ－ｇｕｏ；ＺＨＡＮＧＣｈｕｎ－ｇｕａｎｇ；ＳＵＮＤｅ－ｊｕｎ；ＨＡＮＳｈｕ－ｈｕａａｎｄＷＡＮＧ...     

The Effect of pH Difference Between Two Phases on the Partition of Lysozyme in Aqueous Two-Phase System

Aqueoustwo-phasesystems(ATPS)areformedwhentwoaqueoussolutionsofhydrophilicpolymersorapolymerandasaltaremixedathighconcentration.Forthechargedproteins,AlbertssonhasdevelopedtheclassicalmodelfortheelectrochemicalpartitioninginATPSfInK,=lnK, (Z,F/RT)Arp(l)HereK,denotesthepartitioncoefficientofproteins,InK,includesalltheotherfactorsaffectingproteinpartitioning,and(Z,F/RT)A(PistheelectrostatictermasaproductofproteinsurfacechargeZPandAam,theelectrostaticpotentialdifferencebetweenthetwopha…     

Studies of the Atrazine Aqueous Suspension Stability in the Presence of an Anionic Polymer—Influences of Polymer Molecular Weight and Solution pH

The influence of the molecular weight of sodium salt of styrene/methacrylic acid (SSMA) copolymers and solution pH value (range of 3–11) on the stability of the atrazine suspension was studied. SSMA with different molecular weights was synthesized by emulsion polymerization. Adsorption, zeta potential measurements, microscopy, and suspension stability measurements were carried out. The obtained results indicate that the adsorption of SSMA on the surfaces of atrazine particles decreases with the increase of the molecular weight, and the hydrogen bonding is the main adsorption force. The presence of SSMA improves the stability of the atrazine suspension. The stability of the atrazine suspension decreases with the increase of the molecular weight of SSMA. On the other hand, the stability of the atrazine suspension with SSMA increases firstly and then decreases with the increase in solution pH in the range of 3–11.     

Effect of Dispersant on the Colloidal Stability of Nano‐sized CuO Suspension

The stabilization of nano‐sized CuO suspensions was examined to look for the primary mechanism of dispersion. The dispersion stability of suspension was characterized by sedimentation tests, Zeta potential, granularity tests, and infrared spectroscopy (IR). Influence factors such as pH and the concentration of the dispersant on the colloidal stability of the suspension were investigated. The results showed that sodium polyacrylate was fit to stabilize the suspension of CuO nanoparticles through electrosteric repulsion. Also, smaller viscosity and better dispersion effects were achieved when sodium polyacrylate mass fraction was 0.4%～0.8% (based on the powder), pH was 10.     

The Rmodynamic Study on the Aqueous Complexation of Metal CationswithN－aceticAcidSubstitutedTetraazamacrocycle

ＴｈｅＲｍｏｄｙｎａｍｉｃＳｔｕｄｙｏｎｔｈｅＡｑｕｅｏｕｓＣｏｍｐｌｅｘａｔｉｏｎｏｆＭｅｔａｌＣａｔｉｏｎｓｗｉｔｈＮ－ａｃｅｔｉｃＡｃｉｄＳｕｂｓｔｉｔｕｔｅｄＴｅｔｒａａｚａｍａｃｒｏｃｙｃｌｅＴｈｅＲｍｏｄｙｎａｍｉｃＳｔｕｄｙｏｎｔｈｅＡ...     

Capacitance Characterization of the Effect of pH Value on the Self—assembled Monolayers of Octadecanethiol

In this paper,the membrane capacitance(Cm),which was obtained from the ecectrochemical impedance spectroscopy(EIS) method,was used to characterize the effect of pH value on the self-assembled monolayers(SAMs) of octadecanethiol(18SH) for the first time.The results not only strongly proved that inorganic ions could penetrate the SAMs of 18SH,but also ascertained that SAMs of 18SH were not an absolute of free of ion-penetration.Verifying the existence of pin-holes in the octadecanethiol SAMs was the main contribution of this paper,which coincided with the former conjecture very well.     

Effect of pH on the Hydrothermal Synthesis of BN Nanocrystals

Boron nitride (BN) has been synthesized using hydrothermal synthesis method. The experimental results showed that the pH value of the reaction solution has an important effect on the yield and phases of BN samples. As the pH value decreased, the content of cBN increased and the yield improved. The increase in cBN content is resulted from the conversion of oBN into cBN under hydrothermal condition, and the growth of cBN nanocrystals may due to the decrease in the reaction speed, thus the crystalline perfection of BN improved when the pH value decreased.     

Effect of ionic strength on the stabilities of ciprofloxacin – Metal complexes

Proton–ligand dissociation constant of 1-cyclopropyl-1,4-dihydro-4-oxo-7-(1-piperazinyl) quinolone-3-carboxylic acid is ciprofloxacin and metal–ligand stability constants of its complexes with some metal ions have been determined potentiometrically in the presence of (0.01, 0.02 and 0.03 mol/dm³) NaClO₄. The order of the stability constants of the formed complexes increases in the sequence Cu²⁺, Fe³⁺, Ni²⁺ and Zn²⁺ and decreases with increase in the concentration of ionic strength.     

Investigation On the Behavior of Poly(acrylic acid) in Water Solution and Its Effect on the Rheology of α- Al2O3 Suspension

The influence of pH, relative molecular weight and concentration of poly(acrylic acid) (PAA) on the viscosity of PAA solution was investigated. It was found that the rheology of PAA solution was closely related to the ionization and conformation of PAA chains. The increasing rigidity and the stretching of polymer chain resulted in a maximum viscosity at pH=8. The viscosity change of PAAsolution with addition of alumina powder was studied. It was found that the suspension viscosity reached its minimum when the amount of ceramic powder and PAA was at a certain ratio. At the same time, the viscosity minimum was also influenced by the particle size of powder.     

Effect of the Metal within Regioisomeric Paddle-Wheel-Type Metal–Organic Frameworks

The effect of metal on the degree of flexibility upon evacuation of metal–organic frameworks (MOFs) has been revealed with positional control of the organic functionalities. Although Co-, Cu-, and Zn-based DMOFs (DMOF = DABCO MOF, DABCO = 1,4-diazabicyclo[2.2.2]octane) with ortho-ligands (2,3-NH₂Cl) have frameworks that are inflexible upon evacuation, MOFs with para-ligands (2,5-NH₂Cl) showed different N₂ uptake amounts after evacuation by metal exchange. Considering that the structural analyses were not fully sufficiently different to explain the drastic changes in N₂ adsorption after evacuation, quantum chemical simulation was explored. A new index (η) was defined to quantify the regularity around the metal based on differences in the oxygen-metal-oxygen angles. Within 2,5-NH₂Cl, the η value becomes larger as the metal are varied from Co to Zn. A large η value means that the structures around the metal center are less ordered. These results can be used to explain flexibility changes upon evacuation by altering the metal cation in this regioisomeric system.     

Effect of β-Cyclodextrin on the Micellization of Cetyltrimethylammonium in Aqueous Solution at High Temperature

Molar volume and conductivity measurements have been carried out at 338.2 K for cetyltrimethylammonium chloride (CTAC) + H₂O and CTAC + β-cyclodextrin (β-CD) + H₂O systems. The apparent critical micelle concentrations, the dissociation degree of the micelle, the transfer free energy for the hydrocarbon chain of CTAC, the standard partial molar volumes of CTAC in aqueous β-CD solution and the stoichoimetry for the inclusion complex of CTAC with β-CD have been determined. The influence of β-CD and its complex on the micellization processes of CTAC are analyzed under this temperature. It is shown that β-CD partly screened the hydrophobic hydrocarbon chain of CTAC molecules from contact with the surrounding medium, and retarded the formation of CTAC micelles in a certain extent. The thermodynamic activity of CTAC is decreased. The β-CD and its complexes do not participate the formation of micelles of CTAC, and the complex have no effect on the micelle properties once the micelles are formed. Based on a simple model, the number of CH₂ groups entered the cavity of β-CD was calculated. The result suggests that β-CD forms strong complex with CTAC, and the stoichoimetry is found to be 2:1. This supports our conductivity results.     

Effect of pH on the reactivity of dipeptides and α-amino acids in the N-acylation

The reaction kinetics of Gly, L-??-Ala, Gly-Gly, L-??-Ala-L-??-Ala and ??-Ala-??-Ala with picryl benzoate in water (40 wt %)-2-propanol was investigated. At pH = 4?C8 the rate constants of N-acylation of the anionic form of dipeptides are less than those of the corresponding amino acid anions, in agreement with their basicity, whereas the relative effective rate constants of reactions depend on pH: in acidic, neutral and slightly alkaline media the k _ef values are higher for the dipeptides, and in a strongly alkaline medium, for the amino acids. These differences are due to the changes in the concentrations of reactive forms of amino acids and dipeptides in the system at varying the medium pH.     

Effect of temperature and pH on the aggregation and the surface hydrophobicity of bovine κ-casein

κ-Casein (κ-CN) aggregation by heating has been studied at pH 7.2 and 5.2 using UV-visible spectrophotometry, sodium dodecyl sulfate polyacrylamide gel electrophoresis, spectrofluorometric study of the 1–8 aniline naphtalene sulfonate (ANS)–κ-CN binding and circular dichroism (CD) spectroscopy. The aggregation process to form aggregates like micelles or submicelles and the structural characteristics of these aggregates were pH dependent. Far-UV CD showed that the aggregates obtained by heating presented changes in the κ-CN secondary structure. Near-UV CD spectra showed a certain degree of tertiary organization in the Tyr environment for the protein heated or unheated, only at pH 5.2. ANS binding at both pH was quite different and depends on the self-association process. Heating produced exposition of hydrophobic binding sites only at pH 7.2, including those in the neighborhood of the κ-CN Trp residue.     

Effect of the Composition of the Aqueous Organic Solvent on the Kinetics of N-Acylation of α-Amino Acids with 4-Nitrophenyl 4-Nitrobenzoate

Equations relating the N-acylation rate constants of glycine, L--alanine, DL-threonine, and L-proline with 4-nitrophenyl 4-nitrobenzoate in water-acetonitrile, water-2-propanol, and water-2-methyl-2-propanol solvents to the composition of the medium were obtained, and reaction rate constants in water were calculated.     

Effect of Larger Pore Size on the Sorption Properties of Isoreticular Metal–Organic Frameworks with High Number of Open Metal Sites

Four isostructural CPO-54-M metal-organic frameworks based on the larger organic linker 1,5-dihydroxynaphthalene-2,6-dicarboxylic acid and divalent cations (M=Mn, Mg, Ni, Co) are shown to be isoreticular to the CPO-27 (MOF-74) materials. Desolvated CPO-54-Mn contains a very high concentration of open metal sites, which has a pronounced effect on the gas adsorption of N₂, H₂, CO₂ and CO. Initial isosteric heats of adsorption are significantly higher than for MOFs without open metal sites and are slightly higher than for CPO-27. The plateau of high heat of adsorption decreases earlier in CPO-54-Mn as a function of loading per mole than in CPO-27-Mn. Cluster and periodic density functional theory based calculations of the adsorbate structures and energetics show that the larger adsorption energy at low loadings, when only open metal sites are occupied, is mainly due to larger contribution of dispersive interactions for the materials with the larger, more electron rich bridging ligand.     

Effect of pH on the Final Connectivity Distribution of the Silicon Atoms in the Stöber Particles

Using ²⁹Si MAS-NMR we investigate the effect of pH on the final connectivity distribution of the silicon atoms in the Stöber particles. Our data suggest that the fraction of the silicon atoms that are ully-connected decreases as the ammonia concentration is increased. This suggests a more negative first shell substitution effect in the precipitated phase (liquid droplet) if condensation reactions are irreversible. A simple model is developed to describe the condensation kinetics in the precipitated phase, and the results support the negative first shell substitution effect. These findings challenge the notion of a positive first shell substitution effect in alkaline conditions.     

Effect of the Loading of Metal Salts on the Formation of Fe–Co Solid Solution Nanoparticles in the IR-Pyrolyzed Chitosan Matrix

Russian Journal of General Chemistry - In this study, metal-carbon nanocomposites have been synthesized via the method of simultaneous formation of bimetallic Fe–Co nanoparticles and carbon...