Microgravimetric Study Research Articles

Enzymatically Polymerized Organic Conductors on Model Lipid Membranes.

Seamless integration between biological systems and electrical components is essential for enabling a twinned biochemical-electrical recording and therapy approach to understand and combat neurological disorders. Employing bioelectronic systems made up of conjugated polymers, which have an innate ability to transport both electronic and ionic charges, provides the possibility of such integration. In particular, translating enzymatically polymerized conductive wires, recently demonstrated in plants and simple organism systems, into mammalian models, is of particular interest for the development of next-generation devices that can monitor and modulate neural signals. As a first step toward achieving this goal, enzyme-mediated polymerization of two thiophene-based monomers is demonstrated on a synthetic lipid bilayer supported on a Au surface. Microgravimetric studies of conducting films polymerized in situ provide insights into their interactions with a lipid bilayer model that mimics the cell membrane. Moreover, the resulting electrical and viscoelastic properties of these self-organizing conducting polymers suggest their potential as materials to form the basis for novel approaches to in vivo neural therapeutics.

Investigation of Surface Adsorption and Electrode Passivation during Electrochemical Oxidation of Redox-Active Organics

Redox-active organic molecules (ROMs) have gained interest as electroactive materials for redox flow batteries (RFBs). Electrochemical properties of ROMs, i.e., their solubility and redox potential, can be tuned through molecular engineering of the base molecule. Previously, we reported values of the apparent anodic charge transfer coefficient α (values approaching 1) associated with the electrochemical oxidation of a model ROM, 4-hydroxy-TEMPO.1 Also, we have proposed an adsorption-mediated mechanism to explain this unusual value of α, and have presented evidence to support the occurrence of adsorbed intermediates. Here, we extend this investigation to gain further insights using techniques of slow-scan voltammetry and electrode cycling, and apply them to other ROMs. We will discuss results of spectroscopic and micro-gravimetric studies, which provide further insights into the physicochemical properties of the adsorbed surface-passivating films. Ramifications of these to implementation of ROMs in flow batteries will be discussed too.[1] N. A. Shaheen, M. Ijjada, M. B. Vukmirovic, R. Akolkar. J. Electrochem. Soc., 167 (2020) 143505. Acknowledgements: Investigation of the model ROM was supported by Breakthrough Electrolytes for Energy Storage (BEES)—an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award #DE-SC0019409. Work completed at Argonne was supported by the Joint Center for Energy Storage Research (JCESR), a U.S. Department of Energy, Energy Innovation Hub, and by the U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists, Office of Science Graduate Student Research (SCGSR) program. The SCGSR program is administered by the Oak Ridge Institute for Science and Education (ORISE) for the DOE. ORISE is managed by ORAU under contract #DE‐SC0014664. All opinions expressed in this paper are the author’s and do not necessarily reflect the policies and views of DOE, ORAU, or ORISE.

The adsorption of perchlorate, sulfate, selenate and water on Au(111)-textured electrodes from aqueous solutions: Simultaneous voltammetric, optical and microgravimetric studies

The adsorption of perchlorate, ClO4−(aq), sulfate, SO42−(aq) and selenate, SeO42−(aq) on Au(111)-textured single crystals from aqueous acidic solutions was examined as a function of the applied potential, E, by simultaneous voltammetry, normal incidence differential reflectance spectroscopy, ΔR/R, and electrochemical quartz crystal microbalance, EQCM, techniques. In particular, ΔR/R vs E data collected in pure 0.1 M HClO4 or the same electrolyte containing either 1 mM Na2SO4 or 1 mM Na2SeO4 could be quantitatively accounted for by using a simple model introduced in similar studies reported earlier in this laboratory. This model regards the ΔR/R response as arising from a sum of contributions from bare and adsorbate covered areas of the surface, which are, in each case, linear functions of the applied potential. Adsorption isotherms for ClO4−(aq), and SO42−(aq) on Au(111) from the literature allowed fitting of the model to data obtained in 1 mM Na2SO4 in 0.1 M HClO4 solutions. The two oxyanions were found to co-adsorb over a wide potential range, with SO42−(aq) fully displacing ClO4−(aq) for E > 1.25 V vs RHE. Analogous ΔR/R measurements involving 1 mM Na2SeO4 in 0.1 M HClO4 solutions combined with the model allowed calculation of the coverage of the two oxyanions as a function of E. The experimental isotherms enabled calculation of the mass densities for the adsorbed oxyanions, ρth, yielding values virtually identical to those derived from EQCM experiments, ρexp, for data recorded in the range ca. E < 0.73 V vs RHE in all three solutions. At higher potentials, however, ρexp were significantly larger than those predicted by the optical measurements, a behavior consistent with water co-adsorption.

Topographically Predicted Vertical Gravity Gradient Field and Its Applicability in 3D and 4D Microgravimetry: Etna (Italy) Case Study

Some geophysical or geodynamic applications require the use of true vertical gradient of gravity (VGG). This demand may be associated with reductions of or corrections to observed gravity or its spatiotemporal changes. In the absence of in situ measured VGG values, the constant value of the theoretical (normal) free air gradient (FAG) is commonly used. We propose an alternative to this practice which may significantly reduce systematic errors associated with the use of constant FAG. The true VGG appears to be better approximated, in areas with prominent and rugged topography, such as alpine or some volcanic regions, by a value based on the modelled contribution of the topographic masses to the gradient. Such prediction can be carried out with a digital elevation model (DEM) of sufficient resolution and accuracy. Here we present the VGG field computed for Mt. Etna (Italy), one of the most active and best monitored volcanoes worldwide, to illustrate how strongly the VGG deviates spatially from constant FAG. The predicted (modelled) VGG field is verified by in situ observations. We also take a look at the sensitivity of the VGG prediction to the resolution and quality of used DEMs. We conclude with discussing the applicability of the topo-predicted VGG field in near surface structural and volcanological micro-gravimetric studies.

In Situ Microgravimetric Study of Ion Exchanges in the Ternary Cu-In-S System Prepared by Atomic Layer Deposition

Reaction mechanisms during the growth of multinary compounds by atomic layer deposition can be complex, especially for sulfide materials. For instance, the deposition of copper indium disulfide (CuInS2) shows a non-direct correlation between the cycle ratio, the growth per cycle of each binary growth cycles, i.e., CuxS and In2S3, and the film composition. This evidences side reactions that compete with the direct Atomic Layer Deposition (ALD) growth reactions and makes the deposition of large films very challenging. To develop a robust upscalable recipe, it is essential to understand the chemical surface reactions. In this study, reaction mechanisms in the Cu-In-S ternary system were investigated in-situ by using a quartz crystal microbalance system to monitor mass variations. Pure binary indium sulfide (In2S3) and copper sulfide (CuxS) thin film depositions on Al2O3 substrate were first studied. Then, precursors were transported to react on CuxS and In2S3 substrates. In this paper, gas-phase ion exchanges are discussed based on the recorded mass variations. A cation exchange between the copper precursor and the In2S3 is highlighted, and a solution to reduce it by controlling the thickness deposited for each stack of binary materials during the CuInS2 deposition is finally proposed.

Microgravimetric study of electrochemical properties of PEDOT/WO3 composite films in diluted sulfuric acid

Poly-3,4-ethylenedioxythiophene composite films with tungsten oxide (PEDOT/WO3) were obtained by potentiodynamic deposition of tungsten oxide from acidic metastable solution of isopolytungstates into poly-3,4-ethylenedioxythiophene film, pre-deposited on an Au-quartz crystal. The electrochemical deposition of tungsten oxide into poly-3,4-ethylenedioxythiophene was investigated by electrochemical quartz microgravimetry (EQCM), the masses of PEDOT and tungsten oxide deposits were estimated. The electrochemical behavior of PEDOT/WO3 composite films with different masses of deposited tungsten oxide was studied by cyclic voltammetry and EQCM in the 0.5 M sulfuric acid electrolyte. The change of the fraction of tungsten oxide in the PEDOT/WO3 composite film results in the change of the slope of the Δf–E dependency in the potential region, corresponding to WVI/WV redox process. It is due to an oppositely directed mass transport (anion and cation) during the redox process in the composite film. The average molar mass of transferred species involved in the redox process in tungsten oxide was estimated to be 26 ± 4 g mol−1. It was shown that the fraction of electrochemically active tungsten oxide deposit is dependent on its mass in the composite, with increase of the mass of tungsten oxide in PEDOT/WO3, the fraction of electroactive tungsten oxide WO3 decreases due to decrease in its active area.

Microgravimetric study of electrodeposition and dissolution of lead dioxide on gold and platinum substrates

Thick lead dioxide layers were electrodeposited on gold and platinum substrates from aqueous solutions of Pb(NO3)2 dissolved in nitric acid and perchloric acid, respectively. The electrodeposition was carried out using cyclic voltammetry and chronoamperometry experiments. The mass changes during PbO2-film formation and dissolution were followed by in situ electrochemical quartz crystal microbalance (EQCM). The electrodeposition of lead dioxide on several types of substrates and in different electrolytes has been widely investigated; however, the mechanism of its dissolution has not been explored, yet. The rate of the reactions occurring during the reduction of the film can be very different depending on the substrates, the electrolytes, the applied potential, and the scan rate. The sweep rate and pH have a small effect on reversibility but highly influences the properties and the deposited mass of lead dioxide layer. At lower concentrations of nitric acid, the PbO2 can be reduced in a larger potential range which is most likely related to the variation of the conductivity of the deposited layer as well as on the nature of the intermediate species.

Electrochemical and microgravimetric studies of poly[3,4-ethylenedioxythiophene]-tyrosinase biocomposite material electrodeposited onto gold electrodes by a sinusoidal voltages method

The electrodeposition of poly(3,4-ethylenedioxythiophene)-tyrosinase (PEDOT-Ty) biocomposite material onto gold electrode has been achieved by means of a sinusoidal voltages (SV) method. The SV method consists in the superimposition of a sinusoidal voltage (sin wave) with fixed frequency and amplitude onto a d.c. potential. The influence of electrochemical parameters like frequency and amplitude of SV signal, d.c. potential value, deposition time, on the electrodeposition process has been investigated. The biocomposite material has been prepared as a thin layer onto quartz crystals coated with gold. The frequency change of the quartz crystal during the electrodeposition of the biocomposite material was recorded simultaneously with the measured current response. The morphology of the deposited PEDOT-Ty coatings was investigated by scanning electron microscopy. The electrochemical behavior of the biocomposite material in aqueous solution was studied by cyclic voltammetry and electrochemical impedance spectroscopy. The use of d.c. potential value of 0.6 V revealed the contribution of the SV component to the electrodeposition process. The PEDOT-Ty modified electrode was used as an electrochemical biosensor in the voltammetric determination of dopamine in the presence of hydroquinone. The analytical performances of the prepared biosensors were also investigated.

Microgravimetric study on the formation and redox behavior of poly(2-acrylamido-2-methyl-1-propanesulfonate)-doped thin polyaniline layers

A comparative study on the potentiostatic polymerization of polyaniline (PANI) in inorganic (sulfuric and perchloric) acid and mixed poly(2-acryalamido-2-methyl-1-propane-sulfonic) (PAMPSA)/inorganic acid solutions is carried out through combined electrochemical and microgravimetric techniques. It is established that polymerization in the presence of small amounts of PAMPSA in the mixed solutions results in immobilization of the polyanions in the PANI layers. The redox behavior of the PAMPSA-doped PANI layers, studied in acidic, neutral and slightly alkaline solutions shows that the electroactivity is preserved up to pH 9. PAMPSA seems to operate as a buffer, providing the necessary protons for the PANI layer in the range pH 7 to pH 9. Detailed microgravimetric measurements in buffer solutions with various cationic (Na + and Cs +) and anionic (Cl − and ClO 4 −) species are used to elucidate the ionic transport occurring in the course of the PANI redox transition in neutral solutions. It is found that cations (different than protons) are involved in the early stage of oxidation whereas the participation of anionic species seems to be limited. Small mass fluxes and minor changes in the viscoelastic properties are observed during the redox transition in neutral and slightly alkaline solutions.

Study of copper electrodeposition from acidic sulfate and perchlorate electrolytes using faradaic impedance spectroscopy and quartz microbalance methods

Copper electrodeposition from acidic sulfate and perchlorate electrolytes is studied. Some measurements are performed with addition of gelatine as a surface active agent. In the course of microgravimetric studies, decrease of the derivative of the electrode mass variation by the consumed charge is found, as compared to the value corresponding to the current efficiency of 100%. The latter is in part related to the effect of the double layer structure on the rate of the consecutive stages of copper recharge (Cu2+ + e → Cu+) and deposition (Cu+ + e → Cu). This effect is most pronounced in the case of solutions containing surface active agents that cause hyperpolarization and extension of the monovalent copper stability range as a result of their adsorption on the electrode surface. The faradaic impedance spectra obtained in sulfate and perchlorate electrolytes evidence at least the difference in the rate constants of recharge and copper deposition in these electrolytes. In both cases, the recharge rate constant is considerably lower than the deposition rate constant. The difference between these constants decreases noticeably at the addition of surface active agents.

Surface Structure, Hydration, and Cationic Sites of Nanohydroxyapatite: UHR-TEM, IR, and Microgravimetric Studies

A multi-technique study devoted to investigate the surface features of nanosized hydroxyapatite (HA) was carried out. UHR-TEM observation provided evidence that HA nanoparticles are constituted by a crystalline core, elongated in the direction of the crystallographic c-axis, coated by an amorphous layer 1−2 nm thick. By means of IR spectroscopy and microgravimetry, the amount of water and hydroxy groups on the surface was evaluated. For the as-prepared material, it was found that the first hydration layer is mainly constituted by H2O molecules interacting through a coordinative bond with Ca2+ in a 1:1 ratio, while hydroxy groups account only for ca. 20% of surface hydration species. Outgassing at increasing temperatures up to 300 °C resulted in a complete surface dehydration, accompanied by a decrease of the capability to readsorb water. Possible changes of the local structure of surface Ca2+ ions were probed by IR spectra of adsorbed CO. The combination of these data with rehydration tests suggested that a significant part of surface Ca2+ ions, once dehydrated, can undergo a relaxation inward the surface, progressively more irreversible as the outgassing temperature increases.

A microgravimetric study of simultaneous adsorption of anions and copper on polycrystalline Pt surfaces

The underpotential deposition of Cu was studied in four different acid electrolytes by simultaneous measurements of cyclic voltammetry and microgravimetry using a electrochemical quartz crystal microbalance. The influence of anions on the Cu monolayer was determined. Among the three desorption peaks observed, the first was found to be very sensitive to the nature of the anion present in solution. This was related to the low coverage of the Pt surface by ad-atoms, in the respective potential range, which yields a weak interaction between the Cu ad-atoms. The monolayer is composed of a first layer of Cu adsorbed on Pt and a second layer of anions adsorbed on the Cu ad-atoms, with each anion occupying two adjacent Cu atoms, with the exception of the Cl- anion which was deposited on only one Cu ad-atom. This structure consequently forms a bi-layer deposit. The modification of voltammetric and massogram profiles by adding Cl- to the perchlorate electrolyte was also analyzed.

Electrochemical microgravimetric study on microcrystalline particles of phenazine attached to gold electrodes

Phenazine solid crystals have been attached to gold electrodes and investigated by cyclic and potential step electrochemical quartz crystal microbalance (ECQM) measurements in the presence of aqueous acidic media. The freshly deposited phenazine layers exhibit a break-in phenomenon. The number of potential cycles required for the layer to be fully electroactive depends on its thickness and also on the nature and concentration of the supporting electrolyte as well as on the scan rate. After the break-in, a considerable amount of solvent molecules remains embedded in the surface layer. The protonated and unprotonated forms of phenazine, whose relative amounts depend on the pH of the contacting solutions, are reduced at different potentials; however, the stable product of the first electron transfer is the respective phenazylium salt. During the second reduction step 5,10-dihydrophenazine and charge-transfer complexes of different compositions are formed. Both the current and microgravimetric responses supplied evidences for the structural rearrangements of the solid phases that accompany the redox reactions. The large separation of the reduction and oxidation peaks relates to the additional energy needed to create the solid/solid interface between the reduced and unreduced or partially reduced forms. The chronoamperometric response shows the characteristics of nucleation and growth kinetics. The phase transformation proceeds with the release of hydration water, and the EQCM response is affected by the strain that develops as a consequence of the phase transformation.

Microgravimetric Study of Electrochemically Controlled Nucleophilic Addition of Sulfite to Polyaniline

The sulfonation of polyaniline (PANI) films by nucleophilic addition of sulfite ion has been controlled through the polymer oxidation state under electrochemical control. The process was monitored by in situ electrochemical quartz crystal microbalance (EQCM), and the polymer oxidation was accomplished by electrode potential steps in sulfite aqueous solutions. The nucleophilic addition of sulfite to PANI only takes place on the oxidized polymer. From the ratio of added mass to the injected charge, the degree of sulfonation has been obtained with a yield as high as 50%. It has been observed that the ion-exchange mechanism during the oxidation-reduction process in the resulting sulfonated polymer is analogous to the polymer produced by electrophilic sulfonation of polyaniline or by copolymerization of aniline with aminosulfonic acids, unlike the ionic exchange observed for unmodified PANI.

Anodic Dissolution of Palladium in Sulfuric Acid: An Electrochemical Quartz Crystal Microbalance Study

Regularities of formation of a palladium oxide layer and its cathodic reduction in 0.5 M H2SO4 at 0.5–1.3 V (SHE) are studied by cyclic voltammetry, x-ray photoelectron spectroscopy, and electrochemical quartz crystal microbalance. A pure Pd plate and a ∼0.5-μm-thick Pd coating on gold-sputtered quartz crystal is used for electrochemical and microgravimetric studies. It is shown that a Pd electrode dissolves electrochemically in 0.5 M H2SO4 when its potential is cycled between 0.5 and 1.3 V. In the case of ∼0.5-μm-thick Pd coating on the gold substrate, the decrease in the electrode weight during one anodic–cathodic cycle is 1.0–1.5 μg/cm2. It is suggested that anodic process at 0.5–1.3 V (SHE) represents electrochemical oxidation of palladium, yielding a surface layer of poorly soluble Pd(OH)2 and/or PdO phases, as expressed by the equation Pd + 2H2O ⇄ (Pd(OH)2/PdO)s + 2H+ + 2e. This surface layer, (Pd(OH)2/PdO)s, undergoes reduction during the cathodic process. About 5% of the total amount of ionized palladium dissolve in electrolyte.

Microgravimetric corrosion study of magnetron-sputtered Co-Cr-Mo and Ni-Cr-Mo alloys in an oxygen-containing atmosphere

A quartz crystal microbalance (QCM) has been used for in situ corrosion studies of magnetron-sputtered Co-Cr-Mo and Ni-Cr-Mo alloys, which are of great importance in various technical and medical applications. The corrosion monitoring has been performed in an oxygen-containing atmosphere and in NaCl solution. The alloys were deposited on quartz substrates by means of DC magnetron sputtering. X-ray photoelectron spectroscopy analysis showed that the composition of the deposits was similar to that of the magnetron-sputtering targets. X-ray diffraction revealed an amorphous structure of the sputtered deposits, while the casting alloys had a crystalline structure. The polarization resistance of sputtered alloys in NaCl solution was higher than the activity of conventional alloys, which implied a superior corrosion resistance of the sputtered deposits. Corrosion was initiated by supplying oxygen gas into a wet argon atmosphere and the QCM detected corrosion with nanogram resolution as the increase in mass. Corrosion currents were calculated from the mass versus time curves. The QCM appeared to be an effective tool for corrosive characterization of sputtered alloys in gaseous environments. A corrosion current calculation in solution was complicated by metal transfer to the liquid phase.

Mixed Cation and Anion Transport during Redox Cycling of a Self‐Doped Polyaniline Derivative in Nonaqueous Media

This work describes a microgravimetric study of the charge compensation process in different supporting electrolyte solutions of propylene carbonate or acetonitrile for a polyaniline derivative, poly (aniline‐co‐N‐propane sulfonic acid aniline), PAPSAH. The viscoelastic properties of thin PAPSAH films were investigated using an electroacoustic impedance technique. These results demonstrate that the film behaves rigidly, validating the use of the Sauerbrey equation for mass measurements with the electrochemical quartz crystal microbalance (EQCM). Both cation and anion participation in the charge compensation process were studied using cyclic voltammetry and EQCM measurements. On a molar basis, the cation and anion contributions during the redox process for thin films of this material are roughly 50% each in supporting electrolytes. The cation and anion participation during the redox process increase in the following order: tetrabutylammonium and , respectively. The significance of these results for applications of self‐doped polyaniline derivatives in nonaqueous media is discussed. © 2000 The Electrochemical Society. All rights reserved.

Microgravimetric study of the influence of the solvent on the redox properties of polypyrrol modified electrodes

The redox behavior of the polypyrrole films in the presence of LiClO 4 salt in different solvents like propylene carbonate (PC), N, N-dimetilformamide (DMF), methanol (MetOH), ethanol (EtOH), acetonitrile (ACN) and water was investigated using simultaneous electrochemical quartz crystal microbalance and cyclic voltammetry experiments. Both charge and mass changes during redox processes were rationalized in terms of multiple regression considering some solvent parameters and ionic transport characteristics. The electroactivity of PPY modified electrodes increase in the sequence PC<DMF<EtOH<MetOH<ACN<water. Also the mass gains in the sequence PC<water<EtOH<DMF<MetOH<ACN, showing clearly the influence of the solvent physico-chemical nature on the electroactivity and electroneutralization processes.

Formation of Close-Packed Silver Nanoparticle Multilayers from Electrostatically Grown Octadecylamine/Colloid Nanocomposite Precursors

The formation of close-packed silver nanoparticle thin films via a two-stage self-assembly approach is described. In the first step, surface-modified silver colloidal particles are extracted from aqueous solution via electrostatic interactions into thermally evaporated fatty amine films. Thereafter, the excess fatty amine molecules in the organic matrix are removed by dissolution in a range of organic solvents of varying dielectric properties. Thermogravimetric and quartz crystal microgravimetric studies indicate that, irrespective of whether the dissolution medium is polar or nonpolar, except for a monolayer of amine molecules in direct contact with the colloidal particle surface, almost complete fatty amine dissolution occurs leading to a considerable increase in the packing density of the silver colloidal particles. While UV−vis spectroscopy measurements of the films after amine removal suggest subtle differences in the final structure of the films prepared from the different solvents, atomic force mic...

Permeametric and microgravimetric studies of sorption and diffusion of water vapor in an unsaturated polyester

A detailed analysis of the sorption equilibrium and the diffusion of water vapor under different activities through an unsaturated polyester resin (UPR) has been undertaken by differential permeation and microgravimetry techniques. The BET-type III sorption isotherm obtained by microgravimetry was analyzed with the Zimm–Lundberg approach to determine the mean cluster size in the UPR film: the latter increases drastically with the water content in the film. The transient permeation flux can be well fitted when a concentration-dependent diffusivity of exponential type is used. From the water content at sorption equilibrium and the steady-state permeability, a mean diffusion coefficient for the steady state can be determined; its decrease with increasing water activity is consistent with the increase in the mean cluster size.