Absence Of Electrolyte Research Articles

A Generalized Model for Describing Particle Formation in the Synthesis of Monodisperse Oxide Particles Based on the Hydrolysis and Condensation of Tetraethyl Orthosilicate

A generalized model considering reaction and diffusion processes as rate determining steps is proposed for the formation of particles from hydrolysis and condensation of tetraethyl orthosilicate (TEOS). Reaction rate constant is assumed to be proportional to contact-surface area of two particles. Diffusion rate constant is given by Fuchs' stability theory with interparticle potential containing van der Waals attraction and electrostatic repulsion. To examine the validity of the model, ammonia-catalyzed reactions of TEOS were carried out in an ethanol–water solution at a water concentration of 11 mol/dm3, an ammonia concentration of 1.0 mol/dm3, and TEOS concentrations of 0.2 and 0.4 mol/dm3 in the presence and in the absence of electrolytes. The experiments included competitive particle growth and seeded and nonseeded reactions. The model quantitatively expressed the results of the competitive growth experiments in which particles with different sizes grew at the same rate. The model gave the expected trend for the effect of ionic strength on particle sizes in the nonseeded reaction and the suppression of secondary particles in the seeded reaction by the addition of an electrolyte KCl. Good estimation was also obtained for transient particle size distributions in the nonseeded reaction and the seeded reaction in which secondary particles were generated.

Electrochemical cell system for voltammetry of high purity solvents

A two-compartment cell system was designed to carry out high purity electrochemical experiments. Features of this cell include a monolithic quartz body, quartz isolation frit, pretreated platinum electrode, hydrogen reference electrode, snap-on cell tops, purified “type I” water, high purity supply gases, fluoropolymer tubing, and gas-tight cell integrity. An advantage of this design is the allowance for internal pre-electrolysis of the test solution. The system was quality tested by obtaining cyclic voltammograms of 0.5 molar sulfuric acid solution. To demonstrate its utility for high purity work, novel cyclic voltammograms of type I water were obtained with a platinum microelectrode in the absence of electrolyte. The water voltammograms exhibited three electroactive features: reduction potential limit near E=−0.2 V versus r.h.e. (H2), oxidation potential limit near E=+1.6 V (O2), and one surface reduction peak at E=+0.4 V. Thus, the voltammetric “potential window” for water was determined to be 1.8 V.

Characterization of Interaction between Butylbenzene Sulfonates and Cetyl Pyridinium Chloride in a Mixed Aggregate System

Surface active short chain alkyl benzene sulfonates, which are known as hydrotropes, interact electrostatically as well as hydrophobically with cationic surfactants. The mixtures of butyl benzene sulfonate (BBS-) with cetyl pyridinium chloride (CPyCl), as shown by surface tensiometry, rheological techniques, and IR and NMR spectroscopy form rodlike micelles or vesicles. These microstructures give rise to highly viscous solutions even at very low concentrations in the millimolar region. The CPy+/BBS- complexes also show similar behavior in the absence of electrolytes. The steric hindrance due to the butyl group to the interaction with CPyCl is at a maximum with tert-butyl benzene sulfonate (TBBS-) as compared to n-butyl benzene sulfonate (NBBS-) and iso-butyl benzene sulfonate (IBBS-). The molecular interactions between surfactant/hydrotrope pairs are simulated using the MM2 force field in the presence and absence of water. The presence of water reduces the electrostatic interaction by solvation and reinfo...

Competitive homolytic and heterolytic dediazoniation mechanisms: Rate constants and product distribution of methoxy-, hydroxy-, and hydro-dediazoniation of 3- and 4-methylbenzenediazonium salts in acidic MeOH/H2O mixtures

The rates and product distribution for methoxy-, hydroxy- and hydro-dediazoniation and the rate constants for disappearance of 3- and 4-methylbenzenediazonium tetrafluoroborate in acidic MeOH/H2O mixtures, in the presence and absence of electrolytes like HCl, NaCl, and CuCl2, are reported. Data were obtained by using a combination of VIS-UV and HPLC techniques. The kinetics and product distributions are completely consistent with competitive homolytic and heterolytic mechanisms, the heterolytic one being predominant at any solvent composition. Heterolytic data are in agreement with the predictions of a DN + AN mechanism; that is, rate determining formation of an aryl cation that reacts immediately with available nucleophiles. Selectivity values, determined from product yields, are low and independent of solvent composition. Product formation is discussed in terms of a preassociation step between aryl cations and the nucleophile, which does not account for much of the trapping, and a nucleophilic attack on a “free” arenediazonium cation. Activation parameters were also determined at 99.5% MeOH: enthalpies of activation are high and entropies of activation are positive, and they are similar to those reported for pure water. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 210–220, 2000

Characterization of Interaction between Butyl Benzene Sulfonates and Cetyl Trimethylammonium Bromide in Mixed Aggregate Systems

Surface-active short-chain alkyl benzene sulfonates which are known as hydrotropes interact electrostatically as well as hydrophobically with cationic surfactants in the same manner as salicylate. The interaction in mixed aggregates of the three isomers of butyl benzene sulfonate (BBS-) and cetyl trimethylammonium bromide (CTAB) has been studied by surface tensiometry and rheological techniques. These mixed aggregates form rodlike micelles, giving rise to highly viscous solutions even at low concentrations. To study the interactions in the absence of electrolytes, CTA/BBS complexes were also obtained separately and characterized by similar techniques. The steric effect due to the structure of the butyl group in butyl benzene sulfonates on the interaction with CTAB has been emphasized during these investigations. The interactions are also characterized by infrared and ultraviolet absorption and nuclear magnetic resonance spectroscopy. Molecular modeling was carried out using an MM2 force field for molecula...

Stability and collapse of monolayers of stearic acid and the effect of electrolytes in the subphase

The stability of monolayers at the liquid–gas interface was studied using stearic acid as a model surfactant. The influence of pH in the presence of different electrolytes in the subphase was investigated through experiments carried out using a Langmuir KSV-5000 film balance. These studies are particularly important with respect to the formation and homogeneity of the deposition of monolayers over solid substrates. The results are also useful in the control of surfactant adsorption on bubble surfaces as well as in the rate of film rupture and froth stability in the flotation process. Experiments were conducted for the area loss versus time for the monolayers of stearic acid spread over different electrolyte solutions (Ca 2+ and Mg 2+) as subphases as a function of pH. The stability of the monolayers increased significantly at high pH values due to ionization of the surfactant and the degree of stability was slightly different for the two electrolytes. The main cause of the instability of the stearic acid monolayer at low pH (5.7) both in the presence and absence of electrolytes is a collapse process which involves formation of three-dimensional nuclei on the monolayer surface. Some mathematical models have been proposed to predict the surface area changes as a function of time. The experimental results obtained in the present work were evaluated and discussed based on the Vollhardt model of collapse through nucleation and growth.

Thermal Properties of Lithium‐Ion Battery and Components

Experimental thermal property data of the Sony US‐18650 lithium‐ion battery and components are presented, as well as thermal property measuring techniques. The properties in question are specific heat capacity , thermal diffusivity (α), and thermal conductivity (k), in the presence and absence of electrolyte [1 M in ethylene carbonate‐dimethyl carbonate EC:DMC, 1:1 wt %)]: The heat capacity of the battery, , is at an open‐circuit voltage (OCV) of 2.75 V and at 3.75 V. The thermal conductivity, k, was calculated from where α was measured by a xenon‐flash technique. In the absence of electrolyte, k increases with OCV, for both the negative electrode (NE) and the positive electrode (PE). For the NE, the increase is 26% as the OCV increases from 2.75 to 3.75 V, whereas for the PE the increase is only 5 to 6%. The dependence of both and k on OCV is explained qualitatively by considering the effect of lithiation and delithiation on the electron carrier density, which leads to n‐type semiconduction in the graphitic NE material, but a change from semiconducting to metallic character in PE material. The overall effect is an increase of and k with OCV. For k this dependence is eliminated by electrolyte addition, which, however, greatly increases the effective k of the layered battery components by lowering the thermal contact resistance. For both NE and PE, the in‐plane k value (measured along layers) is nearly one order of magnitude higher than the cross‐plane k. This is ascribed mostly to the high thermal conductivity of the current collectors and to a lesser extent to the orientation of particles in the layers of electrodes. © 1999 The Electrochemical Society. All rights reserved.

Stability of oil-in-water emulsions stabilised by silica particles

We describe the preparation and properties of oil-in-water emulsions stabilised by colloidal silica particles alone. The charge on the particles and their extent of flocculation, assessed via turbidity measurements, can be modified by pH control and addition of simple electrolytes. The stability of emulsions to both creaming and coalescence is low in the absence of electrolyte, and the effects of adding salt are dependent on the type of salt. In systems containing NaCl, emulsions are less stable once the particles are flocculated. In the presence of either LaCl3 or tetraethylammonium bromide (TEAB), emulsion stability increases dramatically for conditions where the silica particles are weakly flocculated; extensive flocculation of the particles however leads to destabilisation of the emulsions. For TEAB, relatively large emulsions of diameter around 40 µm remain very stable for up to 3 months at salt concentrations corresponding to the onset of coagulation of the colloid. Such emulsions are themselves strongly flocculated.

Hydroxy- and chloro- dediazoniation of 2- and 3- methylbenzenediazonium tetrafluoroborate in aqueous solution

We have measured the rates and product yields of dediazoniation of 2- and 3-methylbenzenediazonium tetrafluoroborate in the presence and absence of electrolytes like HCl, NaCl, and CuCl2 using a recently reported methodology that allows simultaneous determination of product concentrations and rates of product formation and, indirectly, loss of starting material. Activation parameters were also obtained: enthalpies of activation are high, and entropies of activation are positive. All results are consistent with a heterolytic mechanism involving the fragmentation of the arenediazonium ion into a very reactive phenyl cation. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 73–82, 1999

Hydroxy‐ and chloro‐ dediazoniation of 2‐ and 3‐ methylbenzenediazonium tetrafluoroborate in aqueous solution

We have measured the rates and product yields of dediazoniation of 2- and 3-methylbenzenediazonium tetrafluoroborate in the presence and absence of electrolytes like HCl, NaCl, and CuCl2 using a recently reported methodology that allows simultaneous determination of product concentrations and rates of product formation and, indirectly, loss of starting material. Activation parameters were also obtained: enthalpies of activation are high, and entropies of activation are positive. All results are consistent with a heterolytic mechanism involving the fragmentation of the arenediazonium ion into a very reactive phenyl cation. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 73–82, 1999

Possible evidence for the existence of a hairy layer at the surface of polymer latex particles

In this work, an attempt is made to verify the existence of a hairy layer at the surface of polymer latex particles, and determine its thickness under different conditions. Two systems have been studied. In one system, sodium dodecyl sulphate (SDS) and sodium dodecanoate (laurate-SL) were used, separately, as emulsifiers in ab initio (unseeded) emulsion polymerization of styrene carried out at different ionic strengths. At low levels of electrolyte (NaCl in the range 0·00– 0·10M), the hydrodynamic radius (dH) was found to decrease gradually, reaching a minimum value at 0·10M, about 7–9nm smaller than the original value in the absence of electrolyte. At electrolyte levels higher than 0·10M, dH increased monotonically. In the first observation, the results are interpreted in terms of a hairy layer model, which suggests that the thickness of this layer is reduced by the presence of an electrolyte because of charge shielding, while the increased dH at high ionic strength is interpreted in terms of coalescence between latex particles. The extent of the effect depends mainly on the concentration of emulsifier. In the second system, the effect on a seeded emulsion polymerization of styrene was investigated. In this system, a seed latex containing about 10% solids was prepared with SDS as emulsifier. The monomer was then further polymerized at different ionic strengths with no more added emulsifier. The effect on dH was very similar to that of the first system. However, in a previous investigation on this system (Polym. Int., 40 (1996) 307) the rate of seeded polymerization was not affected in the electrolyte range 0·0–0·1M, while it was found to increase with increasing electrolyte level in the range 0·10–0·20M. Post-addition of electrolyte (0·0–0·1M) to the seed latex results in a 4–6nm size contraction due to an increase in the hydrophobicity of the surface, leading to a backward extension away from the aqueous phase. © 1998 Society of Chemical Industry

Effects of Electrolytes on Solubilized States of Water by Aerosol OT Reversed Micelles

Aqueous NaCl, NaNO3, and MgCl2 solubilized by Aerosol OT reversed micelles in isooctane media were determined as a function of surfactant concentration. Three solubilization regions I, II and III were apparent based on chemical shifts of water at given AOT concentrations. The states of water in these regions were examined based on change in near infrared spectra with Rw (= [H2O] / [AOT]), and were found the same in the absence of electrolytes. Water in reversed micelles was bounded, interacted with polar groups of the surfactant, and in swollen micelles, was metabounded and interacted with hydrated polar groups by hydrogen bonds. Water in W/O microemulsions was bulk-like. Based on minimal solubilized water required for swollen micelle and W/O microemulsion formation, bounded and metabounded water in reversed and swollen micelles respectively were shown not affected by these electolytes, whereas bulk-like water in W/O microemulsions was so. Electrolytes effect intensity followed the order of Cl->NO3- for sodium salts and Na+>Mg2+ for chloride salts.

The dyeing of conventional and microfibre nylon 6,6 with reactive dyes. Part 2. α-bromoacrylamido dyes

Conventional decitex and microfibre nylon 6,6 fabrics were dyed using three commercial α-bromoacrylamido reactive dyes at pH 4 in the absence of electrolyte and proprietary levelling agent. Only one of the three dyes displayed good build-up on both conventional decitex and microfibre nylon 6,6 fabrics; generally, dye build-up was greater on conventional decitex fabric. It was observed that a large proportion of adsorbed dye was unfixed and removed by wash-off. The fastness of washed-off dyeings to the ISO C6 C2 wash testm, at each of seven depths of shade (0.1%, 0.5%, 1%, 2%, 3%, 4% and 5% omf), was very good although, in the majority of cases, this was expected in view of the very low colour strengths of the dyeings. Treatment of the dyeings before wash-off with a commercial syntan generally reduced the amount of dye removed during wash-off but altered the colour of the dyeings. Generally, syntan treatment did not improve the wash fastness of the dyeings.

Apparent Anomalies in Surface Excesses Determined from Neutron Reflection and the Gibbs Equation in Anionic Surfactants with Particular Reference to Perfluorooctanoates at the Air/Water Interface

The surface tension and neutron reflectivity of several perfluorooctanoic acid salts with monovalent metal cations have been investigated over a wide range of surfactant, counterion, and co-ion concentrations. Previous interpretations of similar surface tension data have indicated that there is significant dissociation of the counterions from the surfactant layer, leading to a prefactor less than 2 in the Gibbs equation for the surfactant in the absence of electrolyte, which could be interpreted in terms of a depletion layer of surfactant in the region underneath the surfactant ion monolayer. We show that this result is an artifact resulting from the presence of small amounts of divalent cation impurity. Once the divalent ions are removed, we obtain complete consistency between the neutron and surface tension results using a Gibbs prefactor of 2 with no significant subsurface depletion. It is concluded that contamination of anionic surfactants by divalent ions may be the most common cause of inaccurate de...

Adsorption of Polyvinylpyrrolidone onto Polystyrene Latices and the Effect on Colloid Stability

Isotherms have been determined for the adsorption of polyvinylpyrrolidone (PVP) samples of various molecular mass (104 to 2.5 × 106) onto anionic polystyrene (PS) latices from both water and 0.5 M NaCl. The adsorption capacity, Γads, was found to be about 0.7 mg m-2 from water and was independent of the PVP molecular mass. These results were consistent with gel permeation chromatography experiments which indicated that there was no preferential adsorption of high or low molecular mass material. In the presence of 0.5 M NaCl, however, the amount adsorbed was between two and four times greater than that in water, depending on the molecular mass, and high molecular mass material was found to adsorb preferentially. The adsorbed layer thicknesses, δ, were also very different for adsorption from the two solvents. In water, thicknesses of 1−3 nm were obtained, indicating that the molecules were lying flat on the surface in the form of trains. In 0.5 M NaCl, the values of δ increased with increasing molecular mass and were between 4 and 29 nm, indicating a more extended configuration with loops and tails protruding away from the surface into solution. In order to explain the different behavior in the two solvents, it was concluded that, in water, interaction with the PS occurred through the PVP hydrophobic methylene/methine groups and the positive dipole of the amide nitrogen of the pyrrolidone ring. The negative dipole associated with the amide oxygen is directed away from the surface into the solution. In 0.5 M NaCl, interaction occurred predominantly through the hydrophobic groups, since the polar interactions would be screened by the electrolyte present. The effect of PVP on the stability of PS was monitored by turbidity measurements. In the absence of electrolyte, stability was achieved due to electrostatic repulsions between the PS particles whereas in 0.5 M NaCl stability was achieved through steric repulsions for the higher molecular mass PVP samples (i.e. >4 × 104).

Electrolyte Effects on the Surface Tension and Micellization of n-Dodecyl β-d-Maltoside Solutions

Sugar-based surfactants such as polyglucosides are a relatively new class of nonionic surfactants portrayed to be suitable for high-salinity applications. To better utilize such surfactants, it is useful to elucidate the mechanisms of their interactions at various interfaces in the presence and absence of electrolytes and the reasons for their salt tolerance. In this work, the effect of various salts on the surface tension and critical micelle concentration of the nonionic surfactant n-dodecyl β-d-maltoside (DM) was studied. Interestingly, while the packing of DM molecules at the air−water interface was not affected by the nature of salt added, cations and anions were found to have markedly different effects on the surface activity and critical micelle concentration (cmc) of the surfactant. For the same cation Na+, the effect of anions decreases in the order F- > Cl- > SO42- > Br- > PO43- > citrate > I- > SCN-. For the same anion Cl-, the effect of cations follows the order K+ > Na+ > Rb+ > Li+ > Ca2+ > A...

Depletion flocculation of polystyrene latices by water-soluble polymers

The stability of polystyrene latices has been studied in the presence of hydroxyethyl cellulose (HEC) sodium carboxymethyl cellulose (SCMC) and sodium polystyrene sulfonate (SPSS) at various ionic strengths. Only HEC was adsorbed onto the particles from water, whereas all three polymers were adsorbed at high ionic strength. Flocculation, monitored by turbidity measurements, was observed in the absence of electrolyte at critical polymer concentrations (C*) at 0.4%, 0.02% and 0.3% for HEC, SCMC and SPSS, respectively. The flocculation was reversible to dilution and weak shear forces and was attributed to polymer depletion. The results correlated well with predictions from potential-energy calculations incorporating van der Waals, electrostatic, steric and depletion terms. The potential-energy diagrams indicated that concentrations of ca. 0.3%, 0.006% and 0.45% HEC, SCMC and SPSS were required to give a sufficiently deep secondary minimum (ca.–5KBT) for aggregation to occur. C* values obtained experimentally for HEC decreased as the ionic strength of the system increased. This was expected since the only effect of the electrolyte was to compress the particle electrical double layer. In the case of the two polyelectrolytes increasing the ionic strength had a number of effects. As well as reducing the electrostatic potential VE, the depletion potential VD was also reduced, since the depletionlayer thickness and the osmotic pressure of the bulk polymer solution decreased while the steric potential Vs became significant owing to polymer adsorption. The state of aggregation was controlled by the subtle interplay of these forces.

A further microelectrode study of the influence of electrolyte concentration on the kinetics of redox couples

Steady state and fast scan voltammetry at Pt microdisc electrodes were used to investigate the Ru(NH 3) 6 3+/Ru(NH 3) 6 2+ and IrCl 6 2−/IrCl 6 3− couples in 1 mol dm −3 chloride media as well as solutions without added electrolyte. The data were used to estimate thermodynamic and kinetic parameters for these couples and the results are compared with those for the Fe(CN) 6 4−/ Fe(CN 6 3− couple. The shifts in the formal potentials with electrolyte concentration are significant and show that the more highly charged species interact more strongly with the counter-ion of the electrolyte. In the absence of electrolyte, the electron transfer reactions appear to be slower. For the Ru(NH 3) 6 3+/ Ru(NH 3) 6 2+ and IrCl 6 2−/IrCl 6 3− couples, the standard rate constant decreases by a factor of 2–5 (possibly a double-layer effect). This ratio supports the conclusion that the decrease of more than 100 reported for the Fe(CN) 6 4−/ Fe(CN) 6 3− couple results from chemical decomposition of Fe(CN) 6 4− and Fe(CN) 6 3− in the absence of excess cations to give an inhibiting film on the electrode surface. The cations stabilize the anions by ion—ion interactions.

Haemodynamics and fluid balance after intravenous infusion of 1.5% glycine in sheep.

With the aim of studying the pathophysiological background of the "TUR syndrome", we gave six conscious ewes an intravenous infusion of 57 ml/kg of 1.5% glycine solution over 40 min. Isotonic saline infusions served as controls. Central haemodynamics were monitored. The plasma concentrations of protein, K, Na and vasopressin, and plasma osmolality were measured repeatedly for up to 4 h. The urinary excretions of Na, K and osmoles were also followed. Both infusions caused an elevation of the mean arterial pressure. With glycine, the pressure increased from 93 +/- 4 to 112 +/- 12 mmHg (12.4 +/- 0.5 to 14.9 +/- 1.6 kPa) (mean +/- s.d.). The pulmonary capillary wedge pressure increased from 7 +/- 3 to 16 +/- 3 mmHg (0.9 +/- 0.4 to 2.1 +/- 0.4 kPa) and remained slightly elevated. The central venous pressure rose from 2 +/- 3 to 11 +/- 3 mmHg (0.3 +/- 0.4 to 1.5 +/- 0.4 kPa) but returned to baseline within 30 min after the infusion. Infusion of glycine resulted in a decrease in the plasma Na concentration from 144 +/- 3 to 114 +/- 4 mmol/l. The plasma osmolality decreased from 290 +/- 2 to 280 +/- 1 mosmol/l, and remained low. There was a median 6-fold increase in plasma vasopressin concentration, while saline did not elicit vasopressin release. Despite the absence of electrolytes in glycine solution, the urinary excretion of sodium amounted to 106 +/- 40 mmol. We conclude that i.v. infusion of 1.5% glycine solution in sheep causes a transient circulatory strain and natriuresis. Moreover, a vasopressin-mediated reduction of maximal water excretion contributes to persisting hypoosmolality.

Lateral conductance parallel to membrane surfaces: Effects of anesthetics and electrolytes at pre-transition

The effects of dilute salts and anesthetics were studied on the impedance dispersion in the dipalmitoylphosphatidylcholine (DPPC) liposomes. Below the pre-transition temperature, the apparent activation energy for conductance in DPPC-H 2O without salts was equivalent to pure water, 18.2 kJ mol −1. This suggests that the mobile ions (H 3O 4 and OH −) interact negligibly with the lipid surface below the pre-transition temperature. At pre-transition temperature, the apparent activation energy of the conductance decreased by the increase in the DPPC concentrations. The effects of various salts (LiCl, NaCl, KCl, KBr, and KI) on the apparent activation energy of the conductance were studied. Changes in anions, but not in cations, affected the activation energy. The order of the effect was Cl − < Br − < I −. Cations appear to be highly immobilized by hydrogen bonding to the phosphate moiety of DPPC. The smaller the ionic radius, the more ions are fixed on the surface at the expense of the free-moving species. The apparent activation energy of the transfer of ions at the vesicle surface was estimated from the temperature-dependence of the dielectric constant, and was 61.0 kJ mol −1 in the absence of electrolytes. In the presence of electrolytes, the order of the activation energy was F − > Cl − > Br − I −. When the ionic radius is smaller, these anions interact with the hydration layer at the vesicle surface and the ionic transfer may become sluggish. In the absence of electrolytes, the apparent activation energy of the dielectric constant decreased by the increases in halothane concentrations. In the presence of electrolytes, however, the addition of halothane increased the apparent activation energy. We propose that the adsorption of halothane on the vesicle surface produces two effects: (1) destruction of the hydration shell, and (2) increase in the binding of electrolytes to the vesicle surface. In the absence of electrolytes, the first effect predominates and the apparent activation energy is decreased. In the presence of electrolytes, the latter effect predominates and the apparent activation energy is increased.