Electrocapillary Method Research Articles

Electrospinning as Promising Technology for Expanding the Assortment of Fibre-Reinforced Porous Composite Materials and Coatings

Scientific approaches and technological solutions for obtaining fibre-reinforced porous composite materials using the electrospinning method are proposed. A comparative analysis of the methods of electrospinning (electrocapillary and NanospiderTM method) is proposed along with a formulation and technological parameters for electrospinning various polymer systems, including solutions of polyamide, polyvinyl alcohol, polyethylene oxide, and interpolymer complexes. Promising opportunities for application of nonwoven fabrics and fibre-reinforced porous composites in medicine, sanitary hygiene, and for the production of clothing, footwear and packaging materials are shown.

Preparation of single bilayer liposomes by an electrocapillary emulsification method.

The single bilayer liposomes have been prepared by an electrocapillary emulsification technique based on interfacial fluctuation in the absence of surfactant. Electron microscopy showed the liposome to be a unilamellar vesicle with a size generally in the range 60-120 nm.

Coadsorption of 3-methylisoquinoline molecules and perchlorate ions at the mercury—aqueous solution interface

The coadsorption of 3-methyl-isoquinoline (3-MeisoQ) and perchlorate ions has been examined at the mercury—aqueous solution interface by various electrocapillary methods. As a function of the surfactant and anion concentrations, three distinct superficial films have been characterized. At very negative potentials, the perchlorate ions are excluded from the condensed film formed by vertically oriented 3-MeisoQ molecules. At less negative potentials, a transition delimits a region of existence of a mixed film where the superficial organization differs only from that prevailing more negatively by the presence of the adsorbed perchlorate. The third film is present mainly in dilute solutions of 3-MeisoQ or perchlorate.

Interfacial Dehydration by Anesthetics: An Electrocapillary Study of Surface Charge Density of Adsorbed Monolayer

We have proposed that anesthetics destruct the hydration shell of macromolecules irrespective of lipid membranes or proteins. These macromolecular structures are supported by the hydrogen-bonded matrix of water molecules. A loss of this support destabilizes the membranes and proteins. The disordered structures are suboptimal for the assigned biological functions, and anesthesia may ensue. We postulated that the dehydration is prompted mainly by the decrease in the interactions of the surface charges with the water dipole. To prove or disprove the above hypothesis, this study measured the effect of volatile anesthetics (chloroform, halothane, and enflurane) on the surface charge density in adsorbed monolayers by an electrocapillary method. The oil phase was methylisobutylketone (MIBK) with cetyltrimethylammonium chloride (CTAC). The aqueous phase was 0.1 M NaCl. The anesthetics decreased the surface charge density, and the effect paralleled the clinical anesthetic potency. At concentrations that induce surgical stage anesthesia in 50% of the population, these anesthetics reduced the surface charge density by 5%.

An electrocapillarity technique to study interfaces between non-polar and polar fluids

Electrocapillary methods for excitation of capillary-gravitational waves at liquid surfaces have been modified for application to liquid-liquid interfaces. The necessary experimental modifications are described. Typical results are presented for a water-hexadecane interface. The observed propagation of the generated waves accords with theoretical expectation.

Polarographic behaviour of petroleum components in aqueous solutions: Application of electrocapillary measurements and convective adsorption accumulation

Electrocapillary investigations by the drop time method revealed a rather strong surface activity of aqueous petroleum solutions and some petroleum fractions in solutions of base electrolytes at the dropping mercury electrode, depending on the quality of the surfactant. The highest surface activity and sensitivity of analytical determination was found between -0.4 and -0.6 V (S.C.E.). The detection limit of the electrocapillary method was 10-20 μg/l for Diesel oil and up to 5 times higher for petroleum samples. The sensitivity of the measurements at lowest concentrations was increased by convective adsorption accumulation at the surface of the growing drop.

Application of the electrocapillary method for the solubility determination of an organic substance in aqueous electrolyte solutions

Application of the electrocapillary method for the solubility determination of an organic substance in aqueous electrolyte solutions

On the behaviour of molecules of the quinoline group at the water—mercury interface Part II. Electrocapillary study of isoquinoline in solutions containing only an “inert” electrolyte

Isoquinoline has been examined in a 0.5 M Na2SO4 aqueous solution, by using various electrocapillary methods. In the range of small potentials, and rather surprisingly, isoQ and Q present a very similar behaviour, despite the considerable difference in their dipole orientation with respect to the median carbons. Esin-Markov plots and capacity—potential—concentration maps indicate that there is gradual desorption towards negative potentials. Three distinct states (dilute flat molecules, a mixture of flat and erect molecules, and a monolayer with a variable extent of local clusters) have been characterized and their domain of prevalence demarcated. At more negative potentials, a sudden reorientation is observed, which reflects the lack of miscibility between two superficial states internally stabilized by their own set of lateral interactions. The effects of the surfactant concentration, the electrolyte concentration and the temperature on the position of the transition potential are interpreted on the basis of the relative position of two γ=f(E) curves, whose vertical shifts are controlled by the Gibbs isotherm equation, with two distinct discrete values for the superficial excesses corresponding to the two antagonizing monolayers. The most compact of these monolayers is stable in the region with stretches between the phase transition potential and the electrolyte potential, both very sharply defined. Its structure has been determined on the basis of a number of converging facts, such as the limiting value of τ, the values of the capacity and the position of the pzc, extrapolated from the σM=f(E) plots.

On the behaviour of molecules of the quinoline group at the water—Mercury interface: Part II. Electrocapillary study of isoquinoline in solutions containing only an “inert” electrolyte

Isoquinoline has been examined in a 0.5 M Na 2SO 4 aqueous solution, by using various electrocapillary methods. In the range of small potentials, and rather surprisingly, isoQ and Q present a very similar behaviour, despite the considerable difference in their dipole orientation with respect to the median carbons. Esin-Markov plots and capacity—potential—concentration maps indicate that there is gradual desorption towards negative potentials. Three distinct states (dilute flat molecules, a mixture of flat and erect molecules, and a monolayer with a variable extent of local clusters) have been characterized and their domain of prevalence demarcated. At more negative potentials, a sudden reorientation is observed, which reflects the lack of miscibility between two superficial states internally stabilized by their own set of lateral interactions. The effects of the surfactant concentration, the electrolyte concentration and the temperature on the position of the transition potential are interpreted on the basis of the relative position of two γ=f( E) curves, whose vertical shifts are controlled by the Gibbs isotherm equation, with two distinct discrete values for the superficial excesses corresponding to the two antagonizing monolayers. The most compact of these monolayers is stable in the region with stretches between the phase transition potential and the electrolyte potential, both very sharply defined. Its structure has been determined on the basis of a number of converging facts, such as the limiting value of τ, the values of the capacity and the position of the pzc, extrapolated from the σ M=f( E) plots.

Adsorption of phloroglucinol at the mercury/aqueous solution interface

The adsorption of phloroglucinol on mercury electrodes has been studied from 0.5 M NaClO 4 aqueous solution by means of capacitance and electrocapillary methods. Capacitance curves show a condensation type behaviour. Congruence Tests indicate simultaneous congruence at negative surface charges. Frumkin isotherm is obeyed both at constant charge and contant potential. The interaction parameter obtained through Frumkin fit corresponds to a repulsive interaction. A new isotherm based on Free Volume Theory was tried. A model for the structure of the double layer in presence of phloroglucinol has been advanced, based on these results and the available crystallographic data of phloroglucinol and its dihydrate.

ChemInform Abstract: COMPARISON OF DROP‐TIME AND ELECTROCAPILLARY METHODS FOR STUDY OF ADSORPTION OF A NEUTRAL MOLECULE AT THE MERCURY ELECTRODE

Abstract The question of the reliability of the electrocapillary technique for measurement of relative changes of surface tension is investigated for the case of aqueous. 0·03N NaClO 4 and for solutions containing the rigid symmetrical molecule pyrazine. Surface tension and adsorption measurements have been made by drop-time and electrocapillary techniques. Only very small differences of surface tension changes, due to adsorption of pyrazine at various electrode charges, can be detected between the two methods. The surface excess/chemical potential relations derived from the results of the two methods are almost identical. It is concluded that systematic errors in the study of electrochemical adsorption by the electrocapillary method do not normally arise.

Simultaneous specific adsorption of two ionic species: Guanidinium chloride at the mercury-water interface

Mixed specific adsorption on mercury of guanidinium ion and chloride ion from aqueous solutions at 25°C was studied by capacity and electrocapillary methods. Thermodynamic analysis and use of a simple model of the inner layer suggests that the guanidinium ion is adsorbed in the region of the outer Helmholtz plane. This adsorption appears to differ in character from previously studied specific adsorption. It is possibly caused by interaction of the ion with interfacial water.

Simultaneous specific adsorption of two ionic species: Guanidinium chlrodie at the mercury-water interface

Mixed specific adsorption on mercury of guanidinium ion and chloride ion from aqueous solutions at 25°C was studied by capacity and electrocapillary methods. Thermodynamic analysis and use of a simple model of the inner layer suggests that the guanidinium ion is adsorbed in the region of the outer Helmholtz plane. This adsorption appears to differ in character from previously studied specific adsorption. It is possibly caused by interaction of the ion with interfacial water.

Comparison of drop-time and electrocapillary methods for study of adsorption of a neutral molecule at the mercury electrode

The question of the reliability of the electrocapillary technique for measurement of relative changes of surface tension is investigated for the case of aqueous. 0·03N NaClO 4 and for solutions containing the rigid symmetrical molecule pyrazine. Surface tension and adsorption measurements have been made by drop-time and electrocapillary techniques. Only very small differences of surface tension changes, due to adsorption of pyrazine at various electrode charges, can be detected between the two methods. The surface excess/chemical potential relations derived from the results of the two methods are almost identical. It is concluded that systematic errors in the study of electrochemical adsorption by the electrocapillary method do not normally arise.

Analysis of experimental problems associated with dilute solutions in double-layer studies

A careful study of aqueous sodium fluoride solutions was carried out by the electrocapillary method. Detailed attention was given to the adsorption behaviour in dilute solutions and the results are compared with published work. Causes of discrepancies in interfacial tensions obtained directly and indirectly are examined, and found to be significantly reduced by application of appropriate experimental procedures. Localized hydrolysis and complexation effects of mercurous ions are proposed as sources of inconsistent double-layer results by different experimental approaches.

Molecular interpretation of adsorption of furan derivatives and cyclopentanone on the mercury electrode at constant charge

The adsorption of six cyclic organic compounds has been studied at the mercury electrode by means of the electrocapillary method. Results are analysed in terms of isotherms at constant electrode charge. The data can be explained by a molecular representation of the species in the double layer. Comparison was made between saturated and unsaturated 5-membered ring compounds. The effects of chloride and, in particular, sulphate base electrolytes were examined in detail. Standard free energies of adsorption are calculated at the respective charges of maximum adsorption. Comparison of the experimental findings with contemporary theories of the double layer shows unequivocally that the Bockris-Devanathan-Müller model is a superior theory for the understanding of the adsorption of neutral organic molecules.

Adsorption of chloride ions at the mercury/solution interface in LiCl—methanol and HCl—ethanol systems—I

The specific adsorption of Cl − ions on mercury from methanol—lithium-chloride and ethanol—hydrogen-chloride systems has been investigated at 25°C using the capacitance bridge method with a dropping mercury electrode and the electrocapillary method. The results are described quantitatively in terms of the Parsons thermodynamic analysis.

Adsorption of cresols at the mercury-solution interface

The adsorption of cresols at the mercury-solution interface from NaF and from NaOH solutions has been studied by electrocapillary and capacitance methods. An interpretation of results has been attempted with special reference to o-cresol adsorption. The curves obtained in NaF solutions are similar to those obtained for phenol adsorption from neutral media. In NaOH solutions the capacitance minima are well above the capacitance of the supporting electrolyte except when the concentration of cresol is nearly as large as that of the base electrolyte. Adsorption isotherms, pressure-area isotherms, and adsorption potential vs. surface excess curves have been calculated at the p.z.c. These results correspond to a model of four capacitors for the adsorption of o-cresol from NaF solutions, the dielectrics being monolayers of oriented water molecules, flat-as well as vertical-oriented cresol molecules, and a polylayer of flat-oriented cresol molecules. From NaOH solution, however, the adsorption of o-cresol leads only to an incomplete monolayer and an S-shaped adsorption potential curve; the reason is that the adsorbate in this case is the cresoxide ion which exerts a lateral repulsion and undergoes a sharp reorientation. The general model suggested for the adsorption of cresol from neutral or alkaline media consists of six capacitors, the dielectrics constituting monolayers of oriented water molecules, flat- and vertical-oriented cresol molecules, flat- and vertical-oriented cresoxide ions and a polylayer of flat-oriented cresol molecules.

Effect of the nature of the supporting electrolyte on the thermodynamic analysis of the adsorption of organic substances on mercury. Adsorption of ethylene glycol from 0.1 M aqueous solutions of halides

Summary The adsorption of ethylene glycol has been studied from 0.1 M aqueous solutions of NaF, KCl, KBr, and KI using the method of the capillary electrometer. Drop time measurements have also been carried out in the case of NaF solutions. The results are considered from the point of view of possible effects of the presence of specifically adsorbed ions on the thermodynamic analysis carried out both on the surface pressure curves and directly on surface excess data. Particular aspects of the congruence of the adsorption isotherm, and of the model of the adsorption layer are discussed in detail. The extension of the error, which is introduced by an intrinsic failure of the electrocapillary method at anodic charges due to change in the contact angle of mercury, is analysed.

The Adsorption of 2,2′-Bipyridine and Its Ferrous Complex on the the Dropping Mercury Electrode

Abstract The adsorption of 2,2′-bipyridine and its ferrous complex [Fe(bip)3]2+ onto the electrode has been studied both by the electrocapillary method and the impedancebridge method. Electrocapillary curves were obtained by the drop-time method. A peculiar shape was observed in the electrocapillary curve of [Fe(bip)3]2+, which was corrected for in the further thermodynamic treatment by taking into account the data obtained with an impedance bridge. It was found that 2,2′-bipyridine is adsorbed flat in the more positive region. At more negative potentials, the adsorption is also flat at low concentrations of 2,2′-bipyridine, but becomes perpendicular beyond 2×10−3 m. The [Fe-(bip)3]2+ adsorption can be accounted for by a Langmuir isotherm. However, the isotherm for 2,2′-bipyridine adsorption varies with the potential, which can be explained in terms of the change in the adsorption structure.