The pH-dependent surface charging and the points of zero charge

The recently published points of zero charge of metal oxides and related materials are compiled to update the previous compilation. The purity of materials is the most important factor responsible for discrepancies in the literature data. In contrast to the success of new spectroscopic methods in the studies of specific adsorption, the progress in studies of primary surface charging of oxides over recent years is less spectacular.     

pH-dependent surface charging and points of zero charge II. Update

Recently published PZC (points of zero charge) of metal oxides and related materials are compiled to update the previous compilations (M. Kosmulski, Chemical Properties of Material Surfaces, Dekker, New York, 2001; J. Colloid Interface Sci. 253 (2002) 77). The electroacoustic method has been widely used; it has become a standard tool, and it has proved to produce IEP (isoelectric points) comparable with those obtained by means of classical electrokinetic methods. The recently published numerical values of PZC/IEP of various materials corroborate the old results, with one exception: the PZC of magnetite found at pH 8 is substantially higher than the values reported in the old literature. New approaches to the electrokinetics of sparingly soluble salts have recently been proposed; e.g., the hysteresis in electrokinetic curves of (nominally) BaTiO3 has been interpreted in terms of changes in the surface stoichiometry caused by leaching.     

pH-dependent surface charging and points of zero charge. III. Update

The recently published points of zero charge (PZC) of various materials are compiled to update previous compilations [M. Kosmulski, Chemical Properties of Material Surfaces, Dekker, New York, 2001; M. Kosmulski, J. Colloid Interface Sci. 253 (2002) 77; M. Kosmulski, J. Colloid Interface Sci. 275 (2004) 214]. The recent results corroborate the previously found PZC with a few exceptions. The PZC of alumina obtained from the second-harmonic generation response is substantially lower than the PZC obtained by means of standard methods, while for titania the difference is less significant. PZC of Tl2O3 at pH 7.9 was reported for the first time. A surprisingly insignificant temperature effect on the IEP of rutile was found. Recent model studies aimed at explanation of the effect of the nature of 1-1 electrolytes on the course of charging curves and of discrepancies in the PZC of different materials having the same chemical formula are summarized.     

Electron-beam charging of polytetrafluoroethylene

The charging of polytetrafluoroethylene films by irradiation with fast electrons having an energy insufficient for the complete penetration through the entire thickness of the polymer was theoretically analyzed. The calculation results take into account the distribution of both the dose rate and the bulk electron thermalization rate over the film thickness in the approximation of prescribed radiation-induced conductivity of polytetrafluoroethylene. The influence of the parameters of radiation-induced conductivity on the charging behavior and on the time dependence of the transient current detected with the use of the split Faraday cup was examined. It was found that the observed transient current inversion is adequately explained with allowance for the specifics of radiation-induced conductivity in polytetrafluoroethylene.     

The unpredictability of electrostatic charging

Capricious charges: the electrostatic charging that occurs when two surfaces come into contact is familiar to everyone, and has been known for millennia. Nonetheless, the scientific understanding of the phenomenon is poor, and it is not possible to reliably predict which surface will charge positively and which will charge negatively. Recent work shows why electrostatic charging may never be predictable.     

Tribo charging powder coatings

At present tribo-guns have captured a fairly large market share of the electrostatic spraying equipment used in the powder coating industry for powder paint applications. However, powder paint system based on carboxyl functional polyesters and some special powder paint formulations cannot be sufficiently charged with tribo guns to obtain a good deposition efficiency of the powder on the object. Attempts have been made to solve this problem through addition of special additives to the powder coatings premix or to the ready-to-use powder. Additives of this type have been proven not to be ideal because they can have a catalytic activity and thus effect the powder coatings properties. We developed oligomeric additives that enhance the tribo charging of carboxylic polyester resins based powder coatings, without influencing to the kinetics of the curing process and other properties of the coating.     

Quantised charging of monolayer-protected nanoparticles

Metal nanoparticles coated with an organic monolayer, so-called monolayer protected clusters (MPCs), can show quantised charging at room temperature due to their sub-attofarad capacitance arising from the core size and the nature of the protecting monolayer. In this tutorial review, we examine the factors affecting the energetics of MPC charging. In the first section, the underlying physics of quantised charging is outlined and we give an overview of the various methods that can be used to measure single electron transfer to nanoparticles. In the subsequent sections, we discuss how electrochemical measurements can be used to give information on the quantised charging of freely diffusing and films of immobilised MPCs. The predictions of models used to determine MPC capacitance are compared with experimental data from the literature.     

Approaching absolute zero

We start with a brief background to the field of ultracold atoms and degenerate quantum gases and then review research in this field currently in progress in our laboratory in Melbourne. Current experiments include the use of a permanent magnetic film atom chip to create a Bose–Einstein condensate (BEC) of ⁸⁷Rb atoms; the use of a periodic magnetic microstructure on an atom chip to produce a magnetic lattice for trapping ultracold atoms and BECs; and the production of a BEC of ⁶Li₂ molecules, comprising pairs of weakly bound fermionic ⁶Li atoms, and a degenerate Fermi gas of ⁶Li atoms in an optical dipole trap near a Feshbach resonance.     

Romancing the "hidden proteome", Anno Domini two zero zero seven

The mechanism of action and properties of a solid-phase ligand library made of hexapeptides, for capturing the "hidden proteome", i.e. the low- and very low-abundance proteins constituting the vast majority of species in any proteome, be it a cell or tissue lysate or a biological fluid, are here reviewed. Mechanisms of adsorption are evaluated, as well as different protocols for en bloc or sequential elution of the captured polypeptides. Examples are given of capture of proteins from serum, human platelet extracts, bacterial extract and egg white. The increment in detection of low-abundance species appears to be of at least four-fold as compared with untreated samples. One particular aspect of this capture is the adsorption of a high proportion of small peptides (in the Mr 600-8000 Da range) that are normally lost upon electrophoretic two-dimensional mapping. Such a peptide population, in human sera, may be of particular importance since it may contain protein cleavage products of diagnostic value.     

Atomic scale control of single molecule charging

A scanning tunneling microscope was used to study charging of single copper phthalocyanine molecules adsorbed on an ultrathin Al(2)O(3) film grown on a NiAl(110) surface. A double-barrier tunnel junction is formed by a vacuum barrier between the tip and the molecule and an oxide barrier between the molecule and the NiAl. In this geometry the molecule can be charged by the tunneling electrons. This charging was found to be strongly dependent on the position of the tip above the molecule and the applied bias voltage.     

Magnetoelectrochemistry of gold nanoparticle quantized capacitance charging

Magnetoelectrochemical studies of gold nanoparticle quantized capacitance charging were carried out at ambient conditions. The single electron transfer responses were found to be sensitive to external magnetic fields, reflected in the enhancement of voltammetric peak currents and shifts of peak formal potentials with increasing magnetic field intensities. Additionally, splittings of voltammetric peaks were also observed upon the application of an external magnetic field. These phenomena might be partly attributed to the paramagnetic characters (electron parity) of nanosized gold particles which are contingent upon their charge states. These novel observations suggest that the nanoparticle electronic energy structures can be varied by magnetic fields, leading to molecular manipulations of the nanoscale charge-transfer chemistry.     

Ultrafast intermolecular zero quantum spectroscopy

Clinical magnetic resonance spectroscopy is typically limited by magnetic inhomogeneities which destroy spectral resolution, but intermolecular zero quantum coherences (iZQCs) are insensitive to such inhomogeneities. iZQC resolution in vivo, however, has been hampered by physiological fluctuations over the time scale of the two-dimensional acquisition. A faster iZQC sequence will allow us to average away these fluctuations, and thus we present a new approach to ultrafast two-dimensional spectroscopy. This communication reports iZQC experiments acquiring up to 31 t1-points per scan, as well as extensions to a broad range of other 2D sequences.     

The potential of zero charge of jellium

A model of the interface metal/electrolyte is presented in which the metal is represented as jellium, the solvent as an ensemble of dipoles. The potential of zero chase of the interface is calculated for various electronic densities of the jellium. The results are discussed with respect to experimental data.     

Electron-beam charging of poly(methyl methacrylate)

The charging of bulk poly(methyl methacrylate) by irradiation with electrons of 2 MeV energy at room temperature in vacuum was studied. The experimental data obtained using the split Faraday cup are compared with the results of numerical simulation assuming one-dimensional geometry with allowance for the spatial distribution of dose rate and injected-electron current, nonlinear properties of radiation-induced conductivity in the prebreakdown electric-field region, and the intrinsic conductivity of poly(methyl methacrylate). It was shown that published data on the electric field strength measured by means of the electro-optical Kerr effect in electron-beam charged poly(methyl methacrylate) agree satisfactorily with the calculation results.__________Translated from Khimiya Vysokikh Energii, Vol. 39, No. 3, 2005, pp. 183–189.Original Russian Text Copyright © 2005 by Sadovnichii, Tuytnev, Milekhin.     

Characterization of mineral oxide charging in apolar media

This paper presents an investigation of the charging behavior of mineral oxide particles dispersed in apolar media. There are a growing number of applications that seek to use electrostatic effects in apolar media to control particle movement and improve aggregation stability. Progress is limited, however, by incomplete knowledge of the mechanism(s) of particle charging in these systems. It has been shown in a number of cases that the acid-base properties of both the particles and the surfactants used to stabilize charge play key roles. A mechanism for acid-base charging has previously been established for mineral oxides in aqueous systems, where the surface hydroxyl groups act as proton donors or receivers depending on the pH of the surrounding solution. In water, the pH at which the surface charge density is zero, i.e., the point of zero charge (PZC), can be used to characterize the acid-base nature of the mineral oxide particles. The current work explores the possible extension of this charging behavior to apolar systems, with the key difference that the surface hydroxyl groups of the mineral oxides react with the surfactant molecules instead of free ions in solution. The apolar charging behavior is explored by measuring the electrophoretic mobility of a series of mineral oxides dispersed in a solution of Isopar-L and AOT, a neutral surfactant in water. The electrophoretic mobility of the particles is found to scale quantitatively, with respect to both sign and magnitude, with their aqueous PZC value. This provides support for the theory of acid-base charging in apolar media and represents a method for predicting and controlling particle charge of mineral oxides dispersed in apolar media.     

Quantized double-layer charging of highly monodisperse metal nanoparticles

We describe unprecedented resolution of electrochemically observed quantized double layer (QDL) charging, attained with use of reduced solution temperatures and with an annealing procedure that produces hexanethiolate monolayer protected gold clusters (C6 MPCs) with a high level of monodispersity in charging capacitance, C(CLU). The spacing DeltaV = e/C(CLU) on the electrochemical potential axis between one electron changes in the electronic charge of nanoscopic metal particles is determined by their effective capacitance C(CLU). The high monodispersity of the C6 MPCs with Au(140) cores facilitates (a) detailed rotated disk and cyclic voltammetric measurements, (b) simulation of QDL waveshapes based on assumed reversible, multivalent redox-like behavior, (c) determination of nanoparticle diffusion rates, and (d) observation of as many as 13 changes in the MPC charge state, from MPC(6-) to MPC(7+). The single electron QDL charging peaks are quite evenly spaced (DeltaV constant) at potentials near the MPC potential of zero charge, but are irregularly spaced at more positive and negative potentials. The irregular spacing is difficult to rationalize with classical double layer capacitance ideas and is proposed to arise from a correspondingly structured (e.g., not smooth) density of electronic states of the nanoparticle core, resulting from its small HOMO/LUMO gap and incipiently molecule-like behavior.     

Ion-induced discrete charging of immobilized water-soluble gold nanoclusters

Hydrophilic gold nanoclusters were immobilized onto monolayer-modified gold electrodes and PF6-(-)induced rectification and stepwise capacitance charging was studied in aqueous supporting electrolyte by cyclic voltammetry and ac voltammetry.     

Overview of multi-stage charging strategies for Li-ion batteries

To reduce the carbon footprint in the transportation sector and improve overall vehicle efficiency,a large number of electric vehicles are being manufactured.This is due to the fact that environmental concerns and the depletion of fossil fuels have become significant global problems.Lithium-ion batteries(LIBs)have been distinguished themselves from alternative energy storage technologies for electric vehicles(EVs) due to superior qualities like high energy and power density,extended cycle life,a...