Induced asymmetries in the heteroaggregation of oppositely charged colloidal particles

Heterocoagulation of cationic and carboxylated polystyrene latexes is studied for a wide range of salt concentrations by static light scattering. The weak character of the surface groups providing the charges allows variation of the relative charge of the systems. Two situations are studied: both latexes with similar surface charges and with very different ones. In both cases at low ionic concentration pure heteroaggregation takes place, whereas diffusive aggregation is observed at high kappa, above the critical coagulation concentration (C.C.C.) of both latexes. The overall rate of aggregation describes a minimum at intermediate salt concentrations when both latexes bear similar charges. The heterocoagulation rate constant decreases continuously to reach the diffusive value at high salt. An interesting behavior is observed when the latexes have very different charge. The heterocoagulation kinetic constant becomes diffusive above the C.C.C. of the less charged latex.     

Adsorption of Bovine Serum Albumin onto Polystyrene Latex Particles Bearing Saccharidic Moieties

The adsorption of bovine serum albumin (BSA) onto polystyrene latexes bearing various amounts of sugar moieties has been investigated as a function of pH and ionic strength and the results were compared to those for bare polystyrene latexes having negative surface charges. The functionalized latexes were produced by seeded copolymerization of (0.3 μm) liposaccharidic monomer onto polystyrene particles obtained by soap-free emulsion polymerization of styrene using potassium persulfate as initiator. At first, the electrophoretic mobility behavior of the various latexes was examined as a function of pH: a significant decrease was observed in the case of saccharide-containing latex particles compared to the bare particles. The adsorption of BSA onto these latexes exhibited a reduced amount of adsorbed BSA for those latex particles bearing saccharide groups. This adsorbed amount depends on the yield of saccharidic monomer incorporated onto the surfaces of the latex particles.     

Heteroaggregation in binary mixtures of oppositely charged colloidal particles

Heteroaggregation (or heterocoagulation) rate constants have been measured in mixtures of well-characterized colloidal particles of opposite charge with multiangle static and dynamic light scattering. This technique permits routine measurements of absolute heteroaggregation rate constants, also in the presence of homoaggregation. Particularly with multiangle dynamic light scattering, one is able to estimate absolute heteroaggregation rate constants accurately in the fast aggregation regime for the first time. Heteroaggregation rate constants have also been measured over a wide range of parameters, for example, ionic strength and different surface charge densities. Amidine latex particles, sulfate latex particles, and silica particles have been used for these experiments, and they were well characterized with respect to their charging and homoaggregation behavior. It was shown that heteroaggregation rate constants of oppositely charged particles increase slowly with decreasing ionic strength, and provided the surface charge is sufficiently large, the rate constant is largely independent of the surface charge. These trends can be well described with DLVO theory without adjustable parameters.     

Preparation and characterization of carboxylic-containing poly(methyl methacrylate) nanolatexes

Poly(methyl methacrylate) (PMMA)-based latex particles bearing carboxylic groups at the surface were prepared via emulsion polymerization. The polymerization recipe and process were optimized in order to target monodisperse particles with diameters around 100 nm. The polymerizations were performed using 4,4-azobis(4-cyanopentanoic) acid (ACPA) as initiator and sodium dodecyl sulphate (SDS) as surfactant. The polymerization conversion was determined by both gas chromatography and gravimetry. The final latexes were characterized with respect to particle size, size distribution, surface charge density, electrokinetic properties (i.e. electrophoretic mobility vs pH and ionic strength) and colloidal stability (i.e. coagulation rate constants vs pH and stability factor vs ionic strength).     

Colloidal stability of sulfonated polystyrene model colloids. Correlation with electrokinetic data

In this work we describe the colloid stability of functionalized latexes: two sulfonated polystyrene model colloids with the same particle size and different surface charge densities. The critical coagulation concentration (ccc) was determined in the presence of two electrolytes (11 and 22), being around 0.75 M and 0.075 M, respectively. By the DLVO theory the electrokinetic and colloid stability data were correlated to calculate the Hamaker constant at both experimental conditions. By comparing the experimental and theoretical values of the Hamaker constant, it is possible to get more information about the colloidal stabilization mechanism of functionalized latexes. In the case of sulfonated latexes, the electrostatic and seric contributions occur, with different influence for each latex depending of their surface electric charge.     

A kinetic study of oxidation of 1,4‐dioxane by diperiodatonickelate(IV) in aqueous alkaline medium

The kinetics of oxidation of 1,4‐Dioxane (Dio) by Diperiodatonickelate (IV) (DPN) in aqueous alkaline medium at a constant ionic strength of 1.5 mol dm⁻³ was studied spectrophotometrically. The reaction shows first‐order kinetics in [DPN] and less than unit order dependence each in [Dio] and [OH⁻]. Addition of products, Ni(II) and periodate have no significant effect on the reaction rate. An increase in ionic strength and decrease in dielectric constant of the medium increases the rate. A mechanism based on experimental results, involving two paths, one [Dio] dependent and the other [Dio] independent is proposed. The constants involved in the mechanism are evaluated. There is a good agreement between the observed and calculated rate constants at varying conditions of experiments. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 789–796, 1999     

Estimation of kinetic rate constants by turbidity and nephelometry techniques in a homocoagulation process with different model colloids

 In this work turbidimetric and nephelometric techniques have been used to study the homocoagulation of aqueous dispersions of uniform spherical particles of surfactant-free latexes. Cationic and anionic latexes of similar particle sizes (361 and 370 nm) and different surface charge densities (+16.4 and −3.6 μC/cm²) were used throughout. The kinetic constants which control the aggregation processes when the electrical repulsion disappears were estimated by both techniques at different particle concentration and wavelength in order to establish the experimental conditions which provided reliable and similar values for the coagulation rate constant. Both experimental techniques (turbidity and nephelometry) and two ways of fitting the data have been used with both latexes. For the first method, the initial slope of turbidity or total scattered intensity versus time curves were used to calculate the kinetic constants. In the second method, the whole turbidity or total scattered intensity versus time curves were fitted and the kinetic constants calculated. An unambiguous experimental value for the doublet rate constant in diffusion conditions is obtained by turbidity and nephelometry techniques. By nephelometry both data treatments have permitted a distinction between the doublet rate constant and the global rate constant in diffusion conditions. Received: 2 June 1997 Accepted: 14 August 1997     

Novel cationic polyelectrolyte coatings for capillary electrophoresis

The use of bare fused silica capillary in CE can sometimes be inconvenient due to undesirable effects including adsorption of sample or instability of the EOF. This can often be avoided by coating the inner surface of the capillary. In this work, we present and characterize two novel polyelectrolyte coatings (PECs) poly(2‐(methacryloyloxy)ethyl trimethylammonium iodide) (PMOTAI) and poly(3‐methyl‐1‐(4‐vinylbenzyl)‐imidazolium chloride) (PIL‐1) for CE. The coated capillaries were studied using a series of aqueous buffers of varying pH, ionic strength, and composition. Our results show that the investigated polyelectrolytes are usable as semi‐permanent (physically adsorbed) coatings with at least five runs stability before a short coating regeneration is necessary. Both PECs showed a considerably decreased stability at pH 11.0. The EOF was higher using Good's buffers than with sodium phosphate buffer at the same pH and ionic strength. The thickness of the PEC layers studied by quartz crystal microbalance was 0.83 and 0.52 nm for PMOTAI and PIL‐1, respectively. The hydrophobicity of the PEC layers was determined by analysis of a homologous series of alkyl benzoates and expressed as the distribution constants. Our result demonstrates that both PECs had comparable hydrophobicity, which enabled separation of compounds with log P_o/w > 2. The ability to separate cationic drugs was shown with β‐blockers, compounds often misused in doping. Both coatings were also able to separate hydrolysis products of the ionic liquid 1,5‐diazabicyclo[4.3.0]non‐5‐ene acetate at highly acidic conditions, where bare fused silica capillaries failed to accomplish the separation.     

Cationic amino-containing N-isopropyl- acrylamide-styrene copolymer particles: 2-surface and colloidal characteristics

 In a previous paper [1], the synthesis of various polystyrene– poly[NIPAM] core–shell latexes bearing cationic amidino and/or amino charges has been described. Several colloidal properties of these cationic latexes have been charac-terized such as: particle size, surface charge density, electrophoretic mobility and finally colloidal stability. Due to the poly[NIPAM]-rich layer in the shell, it was found that temperature played a significant role on all these properties, a LCST around 33 °C being exhibited. In addition, ionic strength was also found to affect the colloidal behavior of these latexes, the largest effect being observed with latexes having both amidino and amino surface charges. The critical coagulation concentra-tions (CCC) of the various latexes above and below the LCST were determined, highlighting the contribution of electrostatic and steric repulsive forces to the stability of these particles. Received: 20 January 1998 Accepted: 8 June 1998     

Kinetic and Mechanistic Study of the Oxidative Deamination and Decarboxylation of L-Valine by Alkaline Permanganate

Summary.  The kinetics of the oxidation of L-valine, (L-Val) by permanganate in aqueous alkaline medium at a constant ionic strength of 0.50 molċdm⁻³ was studied spectrophotometrically. The reaction is of first order in [permanganate ion] and of fractional order in both [L-Val] and [alkali]. Addition of products has no significant effect on the reaction rate. However, increasing ionic strength and decreasing dielectric constant of the medium increase the rate. The oxidation process in alkaline medium has been shown to proceed via two paths, one involving the interaction of L-valine with permanganate ion in a slow step to yield the products, and the other path the interaction of alkali with permanganate ion to give manganate. Some reaction constants involved in the mechanism were determined; calculated and observed rate constants agree excellently. The activation parameters were computed with respect to the slow step of the mechanism. Received December 30, 1999. Accepted (revised) March 6, 2000     

The Complexation of Some Sodium Sulphophenyl Hydrazo-5-Pyrazolone Dyes Towards Trivalent Lanthanide Ions “Stability Constants”

Acid dissociation constants of substituted-5-pyrazolone dyes have been determined potentiometrically in 75% (v/v) dioxane-water mixture at 30°C and <0.1 ionic strength. The stability constants of their 1:1 and 1:2 chelates with tweleve trivalent lanthanide ions have been determined under the same conditions. The data were correlated and the results were taken to explain the stabilization of such. chelates by dative π -bonding between Ln (III) and the ligand.     

Controlled heterocoagulation of platelets and spheres

We report the controlled heterocoagulation of platelets and spheres, leading to the formation of colloidally stable, anisotropic hybrid particles. Anionically charged, nanosized polymer latex spherical particles were heterocoagulated on the surface of cationically charged hexagonal gibbsite platelets via the adsorption of a single layer of spheres onto both sides of the hexagonal platelets. The latex particles were annealed at a temperature above the Tg of the latex polymer, resulting in a thin polymer layer covering the gibbsite platelets. This heterocoagulation approach enabled the encapsulation of hydrophilic inorganic particles with polymer latexes and the formation of anisotropic hybrid particles.     

Kinetics and mechanism of the photochemical reaction of Octacyanomolybdate (IV) and Diethylenetriamine

Photolysis of [Mo(CN)₈]⁴⁻ in the presence of diethylenetriamine (dien) leads to the complexation of ligand via hydrogen in the stoichiometry 2:1. The mechanism of the complexation was investigated by spectroscopy absorption and the rate constants and the quantum yield determined. Rate constants and quantum yields for the formation of the final products were found to depend on pH, ligand, and metal cyanide concentration. The values are a maximum at pH 7.4. At pH >7.4 the reverse reaction, generating octacyanomolybdate complex from the heptacyano species, is faster. At low pH, the ligand is protonated and less reactive; hence, the rate of reaction and quantum yield values decrease. The ionic strength does not affect the reaction rate, implying an associative mechanism for the photochemical reaction with dien, supported by the rate law. The observed rate law is: © 1999 John Wiley & Sons, Inc. J Chem Kinet 31: 89–93, 1999     

Adding magnetic ionic liquid monomers to the emulsion polymerization tool‐box: Towards polymer latexes and coatings with new properties

Magnetic ionic liquid monomers were synthesized and then polymerized to get magnetic polymer latexes and films. First, a series of 1‐vinyl‐3‐dodecyl‐imidazolium monomers having metal halides counter‐anions such as FeCl₃Br^?, CoCl₂Br^?, and MnCl₂Br^? were synthesized. These ionic liquid monomers were first homopolymerized to lead to magnetic poly(ionic liquids) and characterized. Secondly, magnetic latexes were synthesized by using the magnetic ionic liquids as surfmers (surfactant + monomer) in the emulsion polymerization of methyl methacrylate/n‐butyl acrylate. It was found that the powders obtained by freeze‐drying the latexes presented a paramagnetic behavior with weak antiferromagnetic interactions between the adjacent metal ions. Although the ratio of magnetic ionic liquid/monomer was only 2% these poly(methyl methacrylate‐co‐butyl acrylate) powders and latexes responded to a magnetic field due to the surfmer paramagnetic nature. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1145–1152     

Stability constants and spectroscopic properties of thorium(IV)-arsenazo III complexes in perchloric acid

The complexation of thorium with arsenazo III in perchloric acid was quantitatively investigated with ultraviolet–visible (UV–Vis) absorption spectroscopy. The UV–Vis absorption of both 1:1 and 1:2 (thorium to arsenazo III) complexes in perchloric acid were found to be highly enhanced than the previously reported absorption of the complexes in hydrochloric acid. The stability constants of thorium-arsenazo III complexes were determined via computational analysis, and the SIT (specific ion interaction theory) was employed to evaluate the dependence on ionic strength. This work contributes to a better understanding of the speciation and spectroscopic properties of thorium-arsenazo III complexes at high ionic strength.

     

Kinetic, mechanistic and spectral investigation of ruthenium (III)-catalysed oxidation of atenolol by alkaline permanganate (stopped-flow technique)

Kinetics of ruthenium (III) catalyzed oxidation of atenolol by permanganate in alkaline medium at constant ionic strength of 0.30 mol dm³ has been studied spectrophotometrically using a rapid kinetic accessory. Reaction between permanganate and atenolol in alkaline medium exhibits 1 : 8 stoichiometry (atenolol : KMnO₄). The reaction shows first-order dependence on [permanganate] and [ruthenium (III)] and apparently less than unit order on both atenolol and alkali concentrations. Reaction rate decreases with increase in ionic strength and increases with decreasing dielectric constant of the medium. Initial addition of reaction products does not affect the rate significantly. A mechanism involving the formation of a complex between catalyst and substrate has been proposed. The active species of ruthenium (III) is understood as [Ru(H₂O)₅OH]₂₊. The reaction constants involved in the different steps of mechanism are calculated. Activation parameters with respect to the slow step of the mechanism are computed and discussed and thermodynamic quantities are also calculated.     

Alkaline degradation of the organophosphorus pesticide fenitrothion as mediated by cationic C12, C14, C16, and C18 surfactants

The effect of varying surfactant chain length (C12, C14, C16, C18) on the alkaline hydrolysis of the organophosphorus pesticide fenitrothion was determined for the following series of inert counterion cationic surfactants: dodecyltrimethylammonium bromide (DTABr), tetradecyltrimethylammonium bromide (TTABr), hexadecyltrimethylammonium bromide (CTABr), and octadecyltrimethylammonium bromide (OTABr). Plots of kobs versus [surfactant] at constant [KOH] showed saturation behavior at low total [Br-], and (constrained) S-shaped curvature was observed at high total [Br-]. kobs values increased with increasing surfactant chain length but decreased with added KBr. For systems exhibiting saturation behavior, further analysis of the results using the PPIE treatment as modified to account for HO-/Br- exchange allowed the evaluation of substrate binding constants, KS, and micellar rate constants, k2m. The binding constants increased with chain length (hydrophobicity), but ionic strength had no effect on KS. Meanwhile, because of the increased KS values as the surfactant chain length increased, the rate enhancements observed for fenitrothion degradation correspondingly increased. However, rate enhancements decreased with ionic strength because reactive counterions could not compete against the bromide anion for micellar binding sites. Low k2m/k2w ratios revealed that the observed rate enhancements were due to the so-called concentration effect rather than true catalysis. Finally, where the PPIE model failed (displaying S-shaped curvature), our results support the intervention of sphere-to-rod transitions that are favored at high ionic strength (>0.01 M Br-) and lower temperatures as the cause of the S-shaped curvature.     

Dioxouranium(VI)--carboxylate complexes. Interaction with dicarboxylic acids in aqueous solution: speciation and structure

In this paper we report the results of an investigation performed by potentiometric (H+-glass electrode) and visible spectrophotometric measurements on the interaction of UO2(2+) ion towards some carboxylic ligands (acetate, malonate, succinate, azelate). The measurements were carried out at T= 25 degrees C in different ionic media (KNO3 and NaCl) at different ionic strengths (0.1 < or = I/mol L(-1) < or = 1.0, NaCl; I/mol L(-1) = 0.1, KNO3). The dependence on ionic strength of formation constants was taken into account by using both a simple Debye-Hückel type equation and the SIT (Specific ion Interaction Theory) approach. Different speciation models (depending on concentration of reagents, ionic strength, pH-range) both for different carboxylates and different ionic media have been obtained. Linear combinations between formation constants, stoichiometric coefficients and length of alkyl chain of dicarboxylates have been observed and predicted formation constants at I= 0 mol L(-1) are reported for the interaction of UO2(2+) with HOOC-(CH2)n-COOH with 1 < or = n < or = 7. Finally, a visible absorption spectrum for each complex reaching a significant percentage of formation in solution (KNO3 medium) has been calculated to characterise the compounds found by pH-metric refinement.     

Developments in ion chromatography using monolithic columns

The focus of this review is on current status and on-going developments in ion chromatography (IC) using monolithic phases. The use and potential of both silica and polymeric monoliths in IC is discussed, with silica monoliths achieving efficiencies upwards of 10(5) plates/m for inorganic ions in a few minutes or less. Ion exchange capacity can be introduced onto the monolithic columns through the addition of ion interaction reagents to the eluent, coating of the monolith with ionic surfactants or polyelectrolyte latexes, and covalent bonding. The majority of the studies to date have used surfactant-coated columns, but the stability of surfactant coatings limits this approach. Applications of monolithic IC columns to the separation of inorganic anions and cations are tabulated. Finally, a discussion on the recent commercialization of monolithic IC columns and the use of monolithic phases for IC peripherals such as preconcentrator columns, microextractors and suppressors is presented.     

Kinetic and mechanistic studies on the oxidation of Norfloxacin by Chloramine‐B and N‐Chlorobenzotriazole in acidic medium

The kinetics of oxidation of Norfloxacin [1‐ethyl‐6‐fluoro‐1,4‐dihydro‐4‐oxo‐7‐(l‐piperazinyl)‐3‐quinoline carboxylic acid] by chloramine‐B and N‐chlorobenzotriazole has been studied in aqueous acetic acid medium (25% v/v) in the presence of perchloric acid at 323 K. For both the oxidants, the reaction follows a first‐order dependence on [oxidant], a fractional‐order on [Norfloxacin], and an inverse‐fractional order on [H⁺]. Dependence of reaction rate on ionic strength, reaction product, dielectric constant, solvent isotope, and temperature is studied. Kinetic parameters are evaluated. The reaction products are identified. The proposed reaction mechanism and the derived rate equation are consistent with the observed kinetic data. Formation and decomposition constants for substrate–oxidant complexes are evaluated. ©1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 153–158, 1999