Low Dielectric Constant Media Research Articles

Conductivity of tetra-alkylammonium salts in polyaromatic solvents

It is shown that the conductivity of tetra-alkylammonium salts in low dielectric constant media is not greatly affected by the length of the carbon chain of the cation. The effect upon the conductivity of varying the size of anions and cations has been analysed in several pure and mixed solvents using a modified Fuoss–Kraus theory to take into account the activity coefficient of the undissociated electrolyte. The interionic distance parameter of the ion pairs is calculated and shown to be fairly constant, indicating interpenetration of the ions. Also, following on from the preceding paper, the effect upon the conductivity of the local environment around the solute is found to be negligible. The bulk dielectric constant of the solvent is shown to be the major factor affecting the conductivity of salts.

Phospholipids and bile acids as diffusional carriers of Na+ across nonpolar media.

Phospholipids and bile acids, by virtue of their amphiphilic properties, can interact in nonpolar media forming "inverted" structures (micelles) which presumably have an hydrophilic core and might act as diffusional carriers (ionophores) of electrolytes across low dielectric constant media or lipid membranes. The Na+ ionophoretic capability of various purified phospholipids and the modulating effects of bile acids and phosphatidylcholine was examined by: (a) measurement of 22Na+ partition into the organic phase (chloroform) of a two-phase system and (b) direct measurement of the translocation of 22Na+ across a bulk chloroform phase separating two aqueous phases in a Pressman cell. All phospholipids tested, except for phosphatidylcholine, showed ionophoretic capability for Na+ at micromolar concentrations. Cardiolipin and phosphatidylserine were the most efficient Na+ carriers, comparable with monensin, an established Na+ ionophore. In contrast, cholic acid as well as other bile acids demonstrated only marginal or no Na+ ionophoretic capability. However, hydroxylated bile acids (particularly cholic acid), sodium dodecyl sulfate and Triton X-100, which can induce and stabilize inverted structures in lipid membranes, were able to increase 5- to 8-fold the phospholipid-mediated Na+ transport. Interaction of cardiolipin with Na+ in the chloroform phase followed a rectangular hyperbolic function with an apparent Kd within the physiological Na+ concentration range (16.9 +/- 5.1 mM). Addition of cholic acid to the cardiolipin-containing organic phase resulted in a 10-fold increase of maximal Na+ uptake and no change in apparent Kd. The effect of cholic acid on both cardiolipin-mediated Na+ partition and Na+ translocation across the chloroform phase showed a marked dependence on pH, being greater at pH 7.4.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of trace water on non-aqueous silica dispersions

Spherical monodisperse silica particles, of 401 nm diameter, were prepared and sterically stabilised using a non-ionic surfactant. The particles were dispersed in a low dielectric constant organic medium. The effect of trace amounts of water added to the system was investigated by studying the electrophoretic mobility of the particles, the consolidation of the sedimented bed and the rheology of the dispersion. The changes in these three measurements was attributed to the change in surface charge of the silica particles due to the presence of the added water. The theoretical justification for the variable rheology, as exemplified by the high frequency limit of the storage modulus, is qualitatively discussed.

The dispersibility and stability of carbon black in media of low dielectric constant. 2. Sedimentation volume of concentrated dispersions, adsorption and surface calorimetry studies

Sedimentation volumes of coarse flocculated particles of carbon black dispersed with a commercial polyisobutene succinamide dispersing agent in hydrocarbon were used to evaluate interparticle interactions of concentrated dispersions. The sedimentation volume results are reviewed in conjunction with the earlier reported viscosity, stability and zeta-potential data [1] and suggest that a combination of steric and electrostatic interparticle repulsion has an important influence on the large changes in sedimentation volume which occur in the system. A maximum sedimentation volume occurred at a low dispersant level (< 0.25 wt% of the carbon black) after prolonged agitation, and this value was greater than twice the value obtained without dispersant. This could have important practical implications concerning the stability of some concentrated coarse dispersions. Adsorption isotherms show two distinct modes of adsorption, initially a strong adsorption step up to about 3.5—4 wt% dispersant to carbon black extending into a higher adsorption region. The strong adsorption step was explained by the adsorption of basic dispersant on the acidic sites of the carbon black surface and was shown, by flow microcalorimetry, to have an enthalpy of −7.5 kcal/mol decreasing to about −4.7 kcal/mol with increase in surface coverage. The second adsorption step increased with temperature and pore diffusion was suggested as a possible mechanism.

The dispersibility and stability of carbon black in media of low dielectric constant. 1. Electrostatic and steric contributions to colloidal stability

The dispersibility of carbon black in dodecane at various concentrations of a commercial polyisobutene succinamide clearly demonstrates the two mechanisms by which dispersants minimize attractive forces between colliding particles. At dispersant levels of about 1 wt% of the carbon black, steric protection is evidenced by a million-fold decrease in particle-to-particle electrical conductance and twenty-fold decrease in viscosity, but the rates of flocculation are unchanged from those found with no dispersant for these 50 A films are too thin to effectively stabilize the particles as predicted by London—Hamaker theory. At dispersant levels of about 4 wt% of the carbon black, negative zeta potentials climb well above 120 m V and complete deflocculation results, with stability ratios in excess of 5 × 10 4 as is predictable from DLVO theory.

Charge carrier escape rate from electrode–liquid interface

Carrier photoinjection after excitation of low dielectric constant medium has been described in terms of forced diffusion of ions away from image forces at the electrode. The rate of this detachment process is expected to have a characteristic dependence on the strength of applied electric field at the electrode. We describe an extrinsic photoconductivity experiment using a thin layer cell where space charge modification by dark current of the local field due to injection or blocking effects can be made negligible. At high applied fields we find quantitative agreement of photocharge yield with the predicted characteristic behavior. This agreement strongly supports the correctness of the ion detachment model in such systems.

Dissociation behaviour of some mixtures of three component condensation polymers in non‐aqueous media

AbstractTwo three component condensation polymers have been prepared by reaction with formaldehyde from the following groups of monomeric units: (I) p‐chlorophenol, p‐cresol and p‐aminophenol; (II) p‐toluidine, p‐bromoaniline and p‐aminobenzoic acid. The relevant available data regarding the composition and degree of polymerization (DP) of the two copolymers have been used to characterize the samples. The two copolymers have been mixed in various stoichiometric proportions, and the amounts of acidic/basic functional groups expected to be present in a given weight of the mixture, have been calculated. Electrometric titration techniques in non‐aqueous solvents have been used to determine the amount of acidic/basic functional groups present in the copolymer mixtures. An excellent correlation could be obtained between the observed and calculated values. The nature of the titration curves have been interpreted in terms of intramolecular hydrogen bonding, homoconjugation and ion‐association in a medium of low dielectric constant.

Interpolymer complex between poly(ethylene oxide) and poly(acrylic acid): Viscometric studies in THF‐water mixtures

AbstractSystematic studies were performed on interpolymer complex formation between Poly(acrylic acid) (PAA) and poly(ethylene oxide) (PEO) in THF‐water mixtures of different compositions. Viscosity behaviour during complex formation in mixed solvents was found to be entirely different from that observed by other workers in aqueous and in pure organic solvents. The result are interpreted in terms of, (a) preferential solvation of the polymer, (b) Probable change in conformation of the polyelectrolyte moleculer. (c) association of complex molecules in a medium of low dielectric constant, and (d) expected disordering of bound water molecules around PEO by THF. Irrespective of solvent composition, interpolymer complex of PAA and PEO was always found to have 1:1 unit mole ratio.

Small ionic clusters of lithium perchlorate in low dielectric constant media from conductivity data at 293 K

Small ionic clusters of lithium perchlorate in low dielectric constant media from conductivity data at 293 K

Effect of Hydrogen Bonding on the Dissociation of Some Mixtures of Phenolic Oligomers in Nonaqueous Media

Abstract Some structurally and molecularly uniform phenolic oligomers with additional functional groups have been prepared by known methods of stepwise synthesis, and their dissociation behavior in nonaqueous solvent has been studied by electrometric titration techniques. Hyperacidity and stepwise neutralization of some of the functional groups in the oligomer molecules have been interpreted in terms of intramolecular hydrogen bonding, homoconjugation, and ion association in a medium of low dielectric constant.

Mechanism of high conductivity in a medium of low dielectric constant

Mechanism of high conductivity in a medium of low dielectric constant

The influence of hydrogen on the deformation and fracture of the near surface region of solids: proposed origin of the Rebinder-Westwood effect

Results are presented which show the embrittling effect of hydrogen-bearing environments on the near surface region of solids. This effect was indicated by shifts to higher amplitude of the acoustic emission amplitude distributions obtained during low-speed drilling, by the drilling rate, and by scanning electron microscopy. The extent of embrittlement in liquid environments was found to depend on the availability of the hydrogen, which depends on its bonding in the liquid (covalent, partially ionized, ion paired in media of low dielectric constant, etc). The time dependence of this effect is consistent with the permeation of hydrogen in the near surface region. It is proposed that the hydrogen effect on the deformation and fracture of solids is a universal phenomenon affecting the near surface region of metals, ceramics, glasses, semiconductors, ionic crystals, minerals, and rocks (organic solids may be exceptions) and that this embrittlement by hydrogen is one of the origins of the Rebinder-Westwood chemomechanical effect.

Ionic association of lithium perchlorate in low dielectric constant media from very dilute solutions to saturation at 293 and 198 K

Ionic association of lithium perchlorate in low dielectric constant media from very dilute solutions to saturation at 293 and 198 K

Reactivities of the sulphydryl groups of dog hemoglobin

Dog hemoglobin has four sulphydryl groups at positions α 111 (G18) and β 93 (F9), all of which are titratable with mercurials. Only two of these, however, react with non-mercurial sulphydryl reagents. Kinetic results indicate that the reacting site might be the β 93 (F9). An examination of the environment of the α 111 (G18) shows that this sulphydryl must be unreactive towards non-mercurials because of the presence near it of several interacting groups. These are the carboxyl group of Glu 27α, which is only 4.5 Ă away; the carbonyl of Val 107α; and the hydroxyl of Tyr 24α. There is also a strong interaction with the carboxyl of Glu 116α which, though 12 Å away, is separated from the α 111 (G18) not by water but by protein, a low dielectric constant medium. All these interactions would considerably raise the p K of the Cys 111α thiol. Therefore reaction with non-mercurial sulphydryl reagents via nucleophilic attack by the thiol anion becomes impossible. The effect of inositol hexaphosphate on the kinetics of the sulphydryl group reaction was investigated. Inositol hexaphosphate slows down the reaction by a factor of three for a 10 M excess of inositol hexaphosphate per hemoglobin tetramer and makes about 25% of the sulphydryl contents of the β 93 and α 111 sites unavailable for reaction by any sulphydryl reagent.

Dielectric and Mechanical Relaxations in a Nafion Precursor

The dielectric and mechanical properties of a Nafion precursor have been determined from -196 to +80 °C. The material is a partly crystalline perfluorinated polymer containing a SO2F group at the end of each per. fluorinated ether side chain. Four relaxations are observed. labeled 1, fr, IS, and a in order of increasing temperature. The two relaxations can be partially resolved only at very low frequencies (ca. 0.1 Hz). The 7 relaxation is assigned to motion of the SO2F group, fl' to backbone (-(CF 2)-) motions, d to side chain motions (-(CF(CF3)0CF 2)5-), and a to the glass transition. The effect of ionic forces on the properties of polymers has received considerable attention in recent years. 28 Despite this effort, however, a number of factors have still not been elucidated completely, either because of the inherent difficulty of the problem (such as clustering of the ionic groups in media of low dielectric constant) or because of the difficulty of ob- taining an ionic polymer of varying ion contents which has a structurally exact nonionic analogue. The latter is needed in order to be able to separate clearly the effects of ionic inter- actions alone from those due to other factors such as molecular weight, sequence distribution, etc. In the case of copolymers containing acidic groups, the ion content can be varied by utilizing different degrees of neutralization of the carboxylic acid groups 26-41 and by esterification. 7 However, the unique properties of the proton in general, and its participation in hydrogen bonding in particular, confer special properties onto the acidic analogues of these ionomers which may invalidate any direct comparison with the salts. This paper concerns itself with an investigation of a non- ionic material which is the chemical precursor of the family of ionic polymers known as Nafions, developed by Du Pont for use primarily as electrolyte separators. It consists of a tetrafluoroethylene backbone, with a perfluoronated ether side chain which is terminated by an SO2F group (I)

An ESR study of the effect of the medium on the kinetics of the destruction of tert-butyl peroxide radicals

1. Study has been made of the destruction of tert-butyl peroxide radicals in water, methanol, acetic acid, and their binary mixtures. 2. The effect of the medium on the rates of the radical reactions studied here is largely the result of nonspecific radical solvation. 3. Reaction between tert-butyl peroxide radicals can proceed along parallel paths which differ in the conformation of the intermediate state. The effective constant for RO2 destruction is the sum of two constants, one predominating in media of high dielectric constant and the other predominating in media of low dielectric constant.

Double layer interaction of two charged colloidal spherical particles of a concentrated dispersion in a medium of low dielectric constant. Part 4.—Conducting particles in contact

A concentrated suspension of identical charged spherical colloidal particles in a hydrocarbon medium is considered. The concentration of counter-ions in the hydrocarbon, which are of one species, is assumed to be so small that their mean volume density is virtually uniform. The effect of surrounding particles on any two neighbouring particles is accounted for by enclosing these two particles by a symmetrical surface S0 on which the normal derivative of the potential vanishes everywhere. The volume enclosed by S0 equals twice the mean volume per particle. The potential in the hydrocarbon medium satisfies Poisson's equation, an exact solution of which is obtained in terms of tangent-sphere coordinates at particle contact, assuming that the particle surfaces are equipotentials. The electric double layer force between two particles in contact is calculated by using the Maxwell electrostatic stress tensor. It is suggested that, in hydrocarbon media, electric double layer forces are not significant in determining colloid stability.

The double-layer interaction of two charged colloidal spherical particles of a concentrated dispersion in a medium of low dielectric constant: III. Approximation of perfectly conducting particles

We investigate the electric double-layer force between two neighboring, charged identical, spherical colloidal particles O 1 and O 2 of a concentrated dispersion in a hydrocarbon medium. Only one ionic species, constituting the counterion, is present in the hydrocarbon, and this is at such a low concentration that its mean volume density is virtually uniform. To account for the surrounding particles of the dispersion, it is imagined that O 1 and O 2 are enclosed by a symmetrical surface S 0 such that the net charge contained by S 0 is zero. The volume contained by S 0 equals twice the volume per particle, and S 0 can be chosen so that the normal derivative of the potential on S 0 is zero. The potential distribution in the hydrocarbon medium is governed by Poisson's equation and a solution of this equation is obtained as an infinite series expressed in terms of bispherical coordinates. For simplicity, the surfaces of the two particles are assumed to be equipotentials with fixed total surface charge. A general expression for the double layer force is given as an integral involving the Maxwell electrostatic stress and the osmotic pressure. First and second approximations to this force show that at the mean separation between neighboring particles, the double-layer force is attractive, and it is concluded that double-layer effects alone will not stabilize a highly concentrated suspension in a hydrocarbon medium.

ChemInform Abstract: STRUCTURE OF THE IONIC SPECIES IN ORGANOSODIUM COMPOUNDS DISSOLVED IN PI‐ELECTRON DONOR, LOW DIELECTRIC CONSTANT MEDIA

Chemischer InformationsdienstVolume 6, Issue 32 Physical Organic Chemistry ChemInform Abstract: STRUCTURE OF THE IONIC SPECIES IN ORGANOSODIUM COMPOUNDS DISSOLVED IN PI-ELECTRON DONOR, LOW DIELECTRIC CONSTANT MEDIA J. M. ALVARINO, J. M. ALVARINOSearch for more papers by this author J. M. ALVARINO, J. M. ALVARINOSearch for more papers by this author First published: August 12, 1975 https://doi.org/10.1002/chin.197532094AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume6, Issue32August 12, 1975 RelatedInformation

Carrier mediated ion transport through artificial liquid membranes in relation to thermodynamic and structural properties of membrane macromolecules

A study has been made of the carrier mechanism of the migration of cations through a non-aqueous liquid membrane. The liquid membrane is a layer of a solution of an amphipatic polyacid—the alternate copolymer of maleic acid and hexadecyl vinyl ether—in N-octanol. The membrane separates two aqueous solutions containing a mixture of electrolytes NaCl and CaCl 2 at varying pH. A description of the thermodynamic and structural properties of the polymer in N-octanol is given. Flux measurements of cations across the membrane are reported for symmetrical situations (unidirectional fluxes) and in the case of asymmetry when the acid and salt concentrations in the aqueous phase were different. In the latter case, incongruent fluxes of sodium ions are found and the mechanism of countertransport is analyzed quantitatively on the basis of the thermodynamic data relating to the affinities of the polymeric acid sites towards alkali and alkaline-earth metal ions in the low dielectric constant medium.