Jan C. T. Kwak

INFLUENCE OF EXCHANGEABLE CATION COMPOSITION ON THE SIZE AND SHAPE OF MONTMORILLONITE PARTICLES IN DILUTE SUSPENSION

Viscosity and light-transmission measurements of dilute suspensions of montmorillonites having different exchangeable cations were used to calculate relative particle sizes as a function of cation composition, where particle size is expressed as the number of clay plates per tactoid relative to the number of plates per tactoid for Li-montmorillonite, after exchange of Li, Na, K, Cs, and Mg by Ca. Tactoid sizes increased in the order Li < Na < K < Mg < Ca, with the number of plates per tactoid relative to Li-montmorillonite varying from 1.5 for Na- to 6.1 for Ca-montmorillonite. The results for tactoid sizes derived from light transmission and those derived from viscosity data are in reasonable agreement with each other and with literature data for similar systems. Upon exchange of Ca-counterions for Li-, Na-, or K-coun-terions, a sharp initial decrease in tactoid size was observed over approximately the first 30% of cation exchange. Upon further exchange, tactoid sizes changed only slightly, but when Ca was exchanged for Cs or Mg, a much more gradual decrease in particle size was observed.РезюмеИсследовались измерения вязкости и трансмиссии света растворенных суспензии монтмориллонитов с разными обменными катионами для вычисления относительных размеров частиц как функции катионного состава. Размер частиц выражается как число глинистых пластинок на тактоид по отношениж к числу пластинок на тактоид для Li-монтмориллонита после обмена Li, Nа, K, Сs, и Мg ионом Са. Размеры тактоидов увеличивались в порядке Li < Na < K < Мg < Са, с числом пластинок на тактоид относительно к Li-монтмориллониту, изменяющимся от 1,5 для Иа- до 6,1 для Са-монтмориллонита. Результаты для размеров тактоидов, полученные из трансмиссии света и из данных по вязкости, находятся в довольно хорошем согласии между собой, а также с лиитературными данными для похожих систем. Во время обмена Са-противоионов на Li-, Na-, или K-противоионы, наблюдалось сильное начальное уменьшение размеров тактоидов, приблизительно, во время первых 30% катионного обмена. Во время следующего обмена размеры тактоидов изменялись незначительно, но наблюдалось более постепенное уменьшение в размерах частиц когда ион Са обменялся на Сз или Мg. [Е.С.]ResümeeEs wurden Viskositäts- und Lichtdurchlässigkeitsmessungen an verdünnten Suspensionen von Montmorilloniten mit unterschiedlichen austauschbaren Kationen verwendet, um die relativen Teilchengrößen als die Funktion der Kationenzusammensetzung zu berechnen. Dabei wird die Teilchengröße als die Zahl der Tonblättchen pro Taktoid im Verhältnis zur Blättchenzahl pro Taktoid für Li-Montmorillonit nach dem Austausch von Li, Na, K, Cs, und Mg durch Ca ausgedrückt. Die Taktoidgrößen nahmen in der Reihenfolge Li < Na < K < Mg < Ca zu, wobei die Blättchenzahl pro Taktoid im Verhältnis zu Li-mont-morillonit von 1,5 für Na-Montmorillonit bis 6,1 für Ca-Montmorillonit variierte. Die Ergebnisse für die Taktoidgrößen aus den Lichtdurchlässigkeitsmessungen stimmen sowohl mit denen aus den Viskositätsmessungen als auch mit Ergebnissen aus der Literatur für ähnliche Systeme recht gut überein. Nach dem Austausch von Ca-Gegenkationen für Li-, Na- oder K-Gegenkationen wurde eine schnelle anfängliche Abnahme der Taktoidgröße beobachtet, die etwa die ersten 30% des Kationenaustausches betraf. Nach weiterem Austausch veränderte sich die Taktoidgröße nur wenig. Wenn aber Ca für Cs oder Mg ausgetauscht wurde, war eine kontinuierlichere Abnahme der Teilchengröße zu beobachten. [U.W.]RésuméDes mesures de viscosité et de transmission lumineuse de suspensions diluées de montmorillo-nites ayant différents cations échangeables ont été utilisées pour calculer les tailles de particules relatives en fonction de composition de cations, où la taille de particule est exprimée comme le nombre de plaques d’argile par tactoide relativement au nombre de plaques par tactoide pour la montmorillonite-Li, après échange de Li, Na, K, Cs, et Mg par Ca. Les tailles tactoides ont augmenté dans l’ordre: Li < Na < K < Mg < Ca, avec le nombre de plaques par tactoide relatif à la montmorillonite-Li variant de 1,5 pour la montmorillonite-Na, et 6,1 pour la montmorillonite-Ca. Les résultats pour les tailles tactoides dérivés de la transmission lumineuse et ceux dérivés de données de viscosité sont en accord raisonnable, et sont aussi en accord raisonnable avec les données de la littérature pour des systèmes semblables. Lors de l’échange de contre-ions Ca pour des contre-ions Li, Na, ou K, une forte diminution initiale de la taille tactoide a été observée pendant approximativement les premiers 30% d’échange de cations. Lors d’échange supplémentaire, les tailles tactoides n’ont changé que modérément, mais lorsque Ca a été échangé pour Cs ou Mg, une diminution de taille de particule beaucoup plus graduée a été observée. [D.J.]

The binding of cationic surfactants by DNA

Isotherms for the binding of dodecyltrimethylammonium (DTA+) and tetradecyltrimethylammonium (TTA+) ions by DNA in aqueous solution at 30 degrees C are reported. The binding isotherms were determined using a potentiometric technique with cationic surfactant-selective electrodes. The DNA concentrations used are 5 X 10(-4) and 10(-3) equiv./kg, surfactant concentrations varying from 3 X 10(-6) M to the critical micelle concentration. The influence of added NaCl (0.01 M) on the binding process is studied. The binding process is shown to be highly cooperative. Applying the binding theory of Schwarz and of Satake and Yang, binding constants and cooperativity parameters can be calculated. The binding constant K is found to be 1.2kT larger for TTA+ than for DTA+ in salt-free solution, and 1.4kT larger for TTA+ than for DTA+ in 0.01 M NaCl. The cooperativity parameter mu is about 1.1kT larger for TTA+ in salt-free solution, and 1.2kT larger in 0.01 M NaCl. It is concluded that the hydrophobic part of the bound surfactant is not completely immersed in the hydrophobic DNA core, but also interacts with other surfactant molecules. This situation is compared to the case of micelle formation.

Adsorption at the alumina–water interface from mixed surfactant solutions

Abstract Adsorption isotherms for sodium dodecyl sulfate (SDS) and octylphenolpoly(oxyethylene) (Triton X100 or TX100) on acidic γ-alumina from single aqueous surfactant solution and from mixed surfactant solutions are reported. Classical depletion adsorption experiments are employed. Analysis methods for both surfactants in the mixtures are independent of the presence of the second surfactant. Strong synergism is observed for the two adsorbing surfactants. In the Henry (low surface density) region of the adsorption isotherm, the two surfactants adsorb independently. TX100, which has very low adsorption densities in the absence of SDS, is strongly co-adsorbed in the hemimicellar region for SDS. Surfactant adsorption isotherms show remarkable inverse curvatures for SDS at low SDS:TX100 ratio, and for TX100 at high SDS:TX100 ratio. This behavior is best explained by a three-dimensional representation of the adsorption isotherms. Above the mixed micellar cmc, SDS adsorption does not reach a plateau, but continues to increase, while TX100 adsorption decreases. This follows the behavior of free surfactant concentrations calculated using regular solution theory.

NMR studies in surfactant and polymer-surfactant systems: Micelle formation of sodium ω-phenyldecanoate and interaction with poly(ethylene oxide)

Abstract The micellization process of sodium ω-phenyldecanoate and the interaction between this surfactant and poly(ethylene oxide) (PEO) in aqueous solution have been studied, using 1 H NMR spectroscopy. The critical micelle concentration (CMC) and the micellar aggregation number of sodium ω-phenyldecanoate are found to be 0.0121 ± 0.0001 m and 26 ± 1, respectively. Upon micellization, large upfield (low frequency) chemical shifts are observed for the aromatic protons and the methylene protons near the terminal phenyl group, while the shifts of protons attached to methylene carbons near the headgroup are very small. These observations imply that the terminal phenyl group is on average located in the micellar interior. In the presence of PEO, two critical concentrations are observed, corresponding to, respectively, the formation of a polymer-surfactant aggregate and the coexistence of the polymer-surfactant aggregate and surfactant micelle. The first critical concentration, X 1 , is at 0.00885 ± 0.00004 m and is independent of the PEO molecular weight and concentration. The second critical concentration, X 2 , is dependent on PEO concentration. The binding ratio, ( X 2 − CMC)/ C PEO , is 0.44 ± 0.01 ω-phenyldecanoate ion per monomer unit of PEO. In the PEO/ω-phenyldecanoate system large 1 H aromatic ring current-induced shifts are observed for the surfactant protons near or on the terminal phenyl group and for the PEO protons. Very small shifts are observed for the surfactant protons near the head group. These observations suggest that the terminal phenyl group and most of the PEO are in close proximity, and on average in the interior of the polymer-surfactant aggregate.

The binding of cationic surfactants by hydrophobic alternating copolymers of maleic acid

Abstract The binding isotherms of dodecylpyridinium (DP + ) cations and dodecyltrimethylammonium (DTA + ) cations with alternating copolymers of maleic acid with ethylene (MAE), ethyl vinyl ether (MAEVE), styrene (MASt) and indene (MAIn) were determined in the presence of NaCl by using a potentiometric technique based on surfactant-ion-selective solid-state membrane electrodes. Surfactant binding by MAE shows only single-step isotherms. In contrast, MAEVE, MASt and MAIn show a two-step binding isotherm. The first binding step (the stronger binding mode) in the isotherms is due to the interaction of the surfactant with a combined polyion site containing a charged and a hydrophobic group. The second binding step (the weaker binding mode) is always in the same free surfactant concentration region as for the isotherms with MAE at corresponding NaCl concentrations, indicating a binding mainly through electrostatic interaction. The standard free energies of the binding were calculated for MAEVE, MASt and MAIn from the isotherms obtained and compared with the standard free energy for MAE to examine the thermodynamic contribution of the hydrophobic side chains to the binding process.

A study of the temperature dependence of the binding of a cationic surfactant to an anionic polyelectrolyte

Abstract The binding of the cationic surfactant dodecyltrimethylammonium bromide (DTABr) to the anionic polyelectrolyte dextran sulfate is studied by means of a solid-state-surfactant selective electrode in the temperature range 278–323 K. In all systems, the polymer equivalent concentration is 5 × 10 −4 m , the added NaCl concentration is kept constant at 0.01 m . The binding of DTA + to dextran sulfate has been shown to be a highly cooperative process. The temperature dependence of the overall binding constant is found to be small but significant, exhibiting a maximum value between 298 and 303 K. Δ G 0 of the binding process is relatively constant, varying monotonously from −22.6 kJ mol −1 at 278 K to −26.6 kJ mol −1 at 323 K. The standard entropy of binding decreases with increasing temperature, and the enthalpy of binding is endothermic at low temperature and exothermic at higher temperatures. All these observations show a close resemblance to the case of micellar aggregation of surfactants. In particular, the thermodynamic parameters for surfactant—polyion binding at low concentration reported here will be compared with the case of micelle formation of corresponding C 12 surfactants.

Interactions in clay suspensions: The distribution of ions in suspension and the influence of tactoid formation

Abstract Mean ionic activity and anion exclusion data based on membrane equilibria are reported for a series of alkali- and alkaline earth-forms of montmorillonite. Mean ionic activity coefficients can be described rather well by a simple additivity principle, from which counterion activity coefficients are estimated. These latter varied in a regular fashion from 0.1 for Li-form suspensions to as low as 0.01 for the Ca-form. The trend of low counterion activity coefficients for the more strongly preferred ions is reflected as well in the calculated anion exclusion volumes. The results are discussed in terms of the formation of clay tactoids which can be observed in such suspensions. It is demonstrated that tactoid formation model can describe the ionic distributions in suspension for the cases where diffuse double layer theory for single clay plates is inappropriate.

Rheology and binding studies in aqueous systems of hydrophobically modified acrylamide and acrylic acid copolymers and surfactants

Abstract Viscosity data are reported for aqueous solutions of a series of acrylamide-based co- and terpolymers with added surfactants. Polymer composition is systematically varied through ionic content (acrylic acid monomer content and solution pH) and hydrophobicity (alkylacrylamide content and alkyl chainlength). Surfactants used were sodium dodecylsulfate (SDS), diethylhexyl sulfosuccinate (AOT), dodecyltrimethyl ammoniumbromide (DTAB) and nonionic surfactants. For the anionic surfactant SDS, a surfactant selective electrode was used to obtain binding isotherms of SDS with the polymers. The experiments show that in the presence of anionic surfactants, the solutions exhibit a dramatic increase in solution viscosity at concentrations around the surfactant CMC, attributed to interpolymer cross-linking through the formation of mixed micelles involving the hydrophobes from different polymer chains and the surfactant molecules. The viscosity enhancement is found to increase with increasing hydrophobicity of the hydrophobe and decreases with increasing AA incorporation in the polymer. The ionic fraction of the polymer chain (AA) also plays an important role in unfolding the polymer chain through electrostatic repulsion contributing to the viscosity increases at high solution pH. Both rheology and EMF-derived binding isotherms suggest that the viscosity maximum occurs at a low ratio of bound surfactant and hydrophobe monomers of approximately two surfactant molecules per hydrophobe.

The application of surfactant-selective electrodes to the study of surfactant adsorption in collodial suspension

Abstract Surfactant-selective electrodes in which the active agent is a plasticized poly(vinylchloride) membrane containing a dissolved complex of dodecyltrimethylamonium and dodecylsulfate ions have been applied to the study of surfactant adsorption from dilute aqueous solution by colloidal or suspended particles. As examples of the utility of the surfactant selective electrode in such studies, isotherms for the adsorption of dodecyltrimethylammonium (DTA + ) ions on homoionic bentonite clay in the Na + , Ca 2+ and Mg 2+ form in dilute aqueous suspension with and without added electrolyte, and on coal fines from a wash plant fines circuit are reported. In addition, binding curves for the interaction between DTA + and the anionic polyelectrolyte dextransulfate, again in very dilute aqueous solutions, are reported.

The binding of cationic surfactants by hydrophobic alternating copolymers of maleic acid — charge density dependence

Abstract The charge density dependence of the binding of a cationic surfactant, dodecylpyridinium chloride (DPCl), by an alternating copolymer of maleic acid with styrene (MASt), and by an alternating copolymer of maleic acid with ethylene (MAE) is reported. Binding isotherms are determined in the presence of a fixed concentration of NaCl, using a potentiometric technique based on surfactant ion selective, solid state membrane electrodes. In the case of MASt, the binding of DP+ ions is considerably enhanced by a decrease in the charge density (degree of neutralization) of the polyion. This effect is attributed to the contribution of the hydrophobic side groups in the polymer to the binding process. In the case of MAE, which is a less hydrophobic polymer, the influence of the charge density on surfactant binding is much less. For MASt-DP+ a nearly linear relationship between the Gibbs energy of binding and the inverse of the charge density is observed, indicating a contribution per phenyl group to the Gibbs energy of binding of −1.6RT, in good agreement with the reported value estimated from other observations in an earlier publication.