A study of the gold/aqueous electrolyte interphase by modulated reflection spectroscopy

The admittance and differential reflectivity of an electrode of polycrystalline gold in contact with aqueous 0.02 M NaF, KClO₄, 0.01 M Na₂SO₄ and KCl have been measured in the range of potential where the electrode is ideally polarized (?0.7 V to 0.8 V NHE). In NaF and KClO₄ evidence was obtained for the compression of the adsorbed layer of water. The increase of the number of water molecules, with respect to the number in the least original state (at?4μC cm^?2), is 3% at +8 μC cm^?2 and at?17 μC cm^?2. At the potential of zero charge the water dipoles are oriented preferentially with the oxygen towards the metal. In KCl the optical measurements confirm the existence of two types of Au?Cl^? interaction and the covalent character of the bond at the most positive charges.     

On the adsorption of cetyldimethylbenzylammonium chloride at the mercury/electrolyte solution interface

The adsorption of cetyldimethylbenzylammonium chloride (CDBACl) on the hanging mercury electrode is studied in various supporting electrolytes at various temperatures from 1 to 50 degrees C. A condensed film with low capacitance is formed at negative potentials at transition temperatures below approximately 40 degrees C. The decrease of the temperature favors the film formation, and increases the width of the capacitance pit, while its value remains practically constant. Hysteresis phenomena are also observed during different scan directions. Capacitance-time curves at the potentials where the film is formed show in some cases a nucleation and growth mechanism with induction time and studied by the Avrami formulation. At high temperatures an increase of the capacitance with time is observed depending on the CDBACl concentration and slightly on the electrolyte used, and is attributed to the formation of hemimicelles. At high negative potentials a second narrow region with lower capacitance values is observed. This is easily observed at very high temperatures, while it is absent at lower temperatures. It depends upon the concentration of CDBACl and the electrolyte used. The results are different from those obtained for the adsorption of cetyltrimethylammonium bromide on mercury, indicating the importance of interaction between the hydrophobic chains.     

A new radiotracer method of adsorption studies at metal oxide/aqueous electrolyte interface

Adsorption of inorganic ions at the titania/electrolyte solution interfaces has been studies using a radioisotopic technique. Adsorption evaluated from uptake of radioactivity from the solution is compared with that obtained from sediment radioactivity.     

The adsorption and condensed film formation of cetyltrimethylammonium bromide at the mercury/electrolyte interface

The adsorption of cetyltrimethyammonium bromide (CTAB) on a hanging mercury electrode is studied in various electrolyte systems and temperatures. A condensed film is formed at negative potentials and at room temperature only in the presence of KBr. The decrease of the temperature favors the formation of the condensed film. Hysterisis phenomena are observed during the potential scans at both directions. Capacity time curves at the potentials where the film is formed show a nucleation and growth mechanism, with induction time depending on potential, which has been investigated using Avrami formulation and has been explained as a progressive one-dimensional nucleation with constant growth rate. The nucleation rate increases while moving toward more negative potentials. A linear decrease of the capacitance with time was observed in some cases independent of the measuring potential in a relative large potential range. The different types of micelles can affect the adsorption of CTAB on mercury. An unusual capacitance transient observed at a very narrow negative potential range is attributed to the formation of hemicylinders. The condensed film in the presence of the other electrolytes is observed only at high concentrations (1 M) and very low temperatures (5 degrees C).     

A Monte Carlo study of proton adsorption at the heterogeneous oxide/electrolyte interface

Adsorption of protons on a heterogeneous solid surface is modeled using the Monte Carlo (MC) simulation method. The surface of an oxide is assumed to consist of adsorption sites with pK assigned according to a quasi-Gaussian distribution. The influence of the electrostatic interactions combined with the energetic heterogeneity of the surface is examined, and the MC results are compared with the predictions of the mean field theory (MFT). It is demonstrated that the heterogeneity affects strongly the shape of the isotherms while it does not change the location of the common intersection point of the isotherms. On the other hand, introduction of repulsive interactions into the system is found to shift the CIP toward lower values of pH. It is also shown that the MFT, in general, describes correctly the behavior of the system. On the contrary the condensation approximation, used to derive relatively simple expressions for the adsorption isotherms, introduces serious errors unless the surface is strongly heterogeneous. Some practical remarks how to eliminate the errors associated both with the MC simulations and with the theory are also presented.     

Effect of the deaeration on the adsorption of some cationic surfactants at the mercury/electrolyte solution interface

The effect of the deaeration on the adsorption of three cationic surfactants cetyldimethylbenzylammonium chloride (CDBACl), cetyltrimethylammonium bromide (CTAB) and octadecyltrimethylammonium bromide (OTAB) at the mercury/electrolyte solution interface is studied. The deaeration is studied using either nitrogen or helium and the effect of deaeration process and time is also studied. In all cases an effect of the deaeration time is found which is mainly observed at potentials where a condensed film is formed. Capacity-time curves at the potentials where the film is formed show a nucleation and growth mechanism with induction time that depends on the deaeration time. The deaeration slows down the kinetics of the film formation but does not change the equilibrium capacitance value of the film. The decrease of the dissolved gas from the water that perturbs its structure is perhaps the main reason for the behaviour observed during the adsorption of these surfactants.     

Adsorption of procaine at the mercury/electrolyte solution interface

The adsorption of the local anaesthetic procaine hydrochloride at the mercury/electrolyte interface solution is followed using capacitance measurements. The adsorption is studied at various procaine concentrations, in potassium chloride, potassium bromide or potassium fluoride used as supporting electrolytes, and at various pH values and temperatures. Procaine has basic properties with two acidity constants K. The results indicate the way the procaine molecules orientate at the interface. In all cases studied no hemimicelles or condensed film are observed.     

Ellipsometric study of surfactant adsorption at the aqueous solution/air interface

Summary Ellipsometry has been applied to study the adsorption of sodium dodecylsulfate (NaDS) at the air/solution interface of the surfactant in water and aqueous sodium chloride. Results are expressed by the ellipticitye and the anglea which the major axis of the ellipse forms with the plane of incidence of the light. The ellipticity is found to change its sign at low NaDS concentrations and to pass a maximum somewhat below the cmc. Below the maximum the increment in ellipticity Aee is a linear function of the surface excess concentration dodecylsulfate. The slope e/gd this linear relation is found to decrease when inert electrolyte (NaCl) is added. The azimuth anglea increases slightly with NaDS concentration near and above the cmc. The results are discussed in terms of the Drude theory.

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Zusammenfassung Die Adsorption von Natrium Dodecylsulfat (NaDS) an der Oberfläche wäßßriger Lösungen wurde mit Hilfe eines Ellipsometers untersucht. Die Meßergebnisse werden durch die Elliptizität e und den Winkel a zwischen der Hauptachse der Ellipse und der Einfallsebene des Lichtstrahls ausgedrü ckt. Die Elliptizität wechselt ihr Vorzeichen im Bereich geringer Konzentrationen von NaDS und läuft durch ein Maximum etwas unterhalb der cmc des Tensids. Unterhalb des Maximums wird eine lineare Beziehung zwischen dem Inkrement der Elliptizität e und der Oberflächen-Überschußkonzentration von Dodecylsulfat gefunden. Durch Zugabe eines inerten Elektrolyten (NaC1) wird die Steigung e/ stark verringert. Der Azimuth-Winkel a nimmt im Bereich der cmc des Tensids schwach zu. Die Ergebnisse werden im Rahmen der Drude-Theorie diskutiert.

     

Polystyrene latex adsorption at the gold/electrolyte interface

Irreversible deposition of polystyrene latex particles (average diameter, 1.5 microm) on various solid/electrolyte interfaces was studied experimentally by using the direct microscope observation method. The substrate surfaces included bare mica (reference interface), gold covered mica (layer thickness of 50 nm), and solid gold plate. The morphology and thickness of the gold layer on mica was determined by atomic force microscopy. Well-defined transport conditions of particles were created by using the new impinging-jet cell. A characteristic feature of the cell was that the suspension stream was directed obliquely to the interface. This unique characteristic was advantageous allowing one for direct, in situ, observation of particle deposition at metals and other nontransparent interfaces. Experiments performed for various flow intensities indicated that the initial deposition kinetics at all interfaces was identical within the error bounds, in accordance with the model based on the convective-diffusion theory. It was concluded that the limiting flux was governed by the bulk transport rather than by the specific surface interactions.     

Effect of deaeration on the adsorption of a mixture of cetyltrimethylammonium bromide and cetyldimethylbenzylammonium chloride at the mercury/electrolyte solution interface

The effect of deaeration on the adsorption of a mixture of cetyltrimethylammonium bromide and cetyldimethylbenzylammonium chloride at the mercury/electrolyte interface solution is studied using capacitance measurements focusing mainly at very low temperatures. Isochronous capacitance vs potential curves reconstructed from capacitance time curves show that the deaeration depends on the type of inert gas used as well as the deaeration process. The deaeration changes mainly the kinetics of the change of the capacitance with time. In cases where a condensed film is formed, the equilibrium capacitance value does not change with deaeration, indicating that the organization of the surfactants at the interface is not connected with the deaeration. The effect is attributed to the removal of dissolved gases from water.     

New insight of stabilizing electrode/electrolyte interphase:Regulating the specific adsorption of the inner Helmholtz plane

Rechargeable lithium metal batteries own the highest energy density among all electrochemical energy storage devices.Lithium metal anode in those cell system acts as paramount role in promoting high energy density[1].However,lithium anode tends to form dendrite morphology and exhibits huge volume expansion and high reactivity,which induces ultra-low columbic efficiency and out of tolerance cycle performance and even safety hazards[2,3].The lithium dendrite growth behavior is mainly decided by the high surface energy and diffusion barriers for Li ions in lithium batteries which is ascribed to thermodynamics factors and uneven electronic field distribution[1,4,5].During the repeated plating/stripping process,the structure and components of solid–liquid interphase are significantly determined by the deposition thermodynamics and kinetics.In the recent years,advances in characterization technology and the development of high-performance computing method have driven the rapid exploration of the fundamental theory of solid–liquid interphase in lithium batteries.     

On the time dependence of the formation of a condensed film in the adsorption of adenosine at the interface mercury/electrolyte

The formation of a condensed film in the adsorption of adenosine at the interface mercury/electrolyte was investigated by means of the differential capacity-time dependence combined with the potential-step method. A mathematical function is given which approximates the experimentally found time dependence of the film formation. This function can theoretically be derived with the assumption that the mechanism of the formation of the condensed film is similar to that of two-dimensional nucleation in the case of metal deposition. A possible molecular mechanism of film formation is discussed.     

On the adsorption and condensed film formation of dodecyl-, tetradecyl-, hexadecyl-, and octadecyltrimethylammonium bromides at the mercury/electrolyte interface

The adsorption and condensed film formation of dodecyl (DTAB)-, tetradecyl (TTAB)-, hexadecyl (CTAB)-, and octadecyl (OTAB)-trimethylammonium bromides on the hanging mercury electrode is studied in KBr as supporting electrolyte, at various temperatures from 5 to 45 degrees C. A condensed film is formed at negative potentials and at room temperature only in the presence of CTAB. The decrease of the temperature favors the formation of the condensed film. A transition temperature is observed for the film formation. Capacity-time curves at the potentials where the film is formed show a nucleation and growth mechanism, with induction time depending not only on the final potential but also on the initial potential range, although it is in the desorption region. In this temperature range no film is observed for DTAB and TTAB. However, the film is observed for OTAB, but only at higher temperatures, and is more easily formed with increasing temperature. The film is formed in a certain potential region and the nucleation rate increases while moving toward more negative potentials. Hysteresis phenomena are observed during changes of scan direction. The capacity vs time curves for OTAB, where condensed film is formed, are treated using an Avrami plot formulation and have been explained as progressive one-dimensional nucleation with a decrease of the nucleation rate during the overall film formation. The results show a marked effect of the chain length of the alkyl chain on the film formation.     

Temperature dependence of adsorption parameters of n-butanol and n-valeric acid at their adsorption on mercury electrode from aqueous solutions

Adsorption parameters that enter into the Frumkin isotherm and the model of two parallel capacitors are calculated based on the data of the regression analysis of differential capacitance curves of a mercury electrode in solutions of n-butanol and n-valeric acid at 25, 50, and 75°C. The analysis of the temperature dependences of these parameters allowed free energies, entropies, and enthalpies of adsorption to be found. It is shown that the hydrophobic effect, which is associated with the increase in the enthalpy of liquid water when adsorbate molecules leave it, makes a substantial contribution into the adsorption free energy of studied compounds.     

The interphase between mercury and acetone+ nitromethane mixtures with KPF6 as a supporting electrolyte

Differential capacity and interfacial tension measurements were carried out on mercury for acetone+nitromethane mixtures with KPF₆ as a supporting electrolyte. On the basis of Gibbs adsorption equation and Guggenheim's model of the surface phase the composition of the surface layer was estimated for different acetone contents and different charges on the mercury electrode. The results obtained indicate that the positive acetone adsorption is marked at negative charges with maximum at σ_m=?0.07 C m^?2, but is practically non-existent at zero and positive charges.     

Competitive adsorption of fibrinogen and dipalmitoylphosphatidylcholine at the air/aqueous interface

The competitive adsorption of fibrinogen (FB) and DPPC at the air/aqueous interface, in phosphate buffer saline at 25 degrees C, was studied with tensiometry, infrared reflection absorption spectroscopy (IRRAS), and ellipsometry. For FB/DPPC mixtures with 750 ppm (0.075 wt%) FB and 1000 ppm (0.10 wt%) DPPC, the tension behavior was found to be similar to that of FB when alone, even with DPPC and FB being at the interface. Thus, FB interferes with adsorption of DPPC and inhibits its surface tension lowering ability. When FB protein is introduced in the solution after a DPPC monolayer has formed, the adsorption of FB is inhibited by the DPPC monolayer. When a DPPC monolayer is spread onto a solution with a preadsorbed FB layer, the DPPC monolayer excludes FB from the surface and controls the tension behavior with little inhibition by FB. When a DPPC dispersion is introduced with the Trurnit method, or sprayed dropwise, onto an aqueous FB/DPPC surfaces, the DPPC layer formed on the surface prevents the adsorption of FB and dominates the surface tension behavior. These results have implications in controlling the inhibition of lung surfactant tension behavior by serum proteins, when they leak at the alveolar lining layer, and in developing surfactant replacement therapies for alveolar respiratory diseases.