Institute of Physical Chemistry

Lattice oxygen can play an intriguing role in electrochemical processes, not only maintaining structural stability, but also influencing electron and ion transport properties in high-capacity oxide cathode materials for Li-ion batteries. Here, we report the design of a gas-solid interface reaction to achieve delicate control of oxygen activity through uniformly creating oxygen vacancies without affecting structural integrity of Li-rich layered oxides. Theoretical calculations and experimental characterizations demonstrate that oxygen vacancies provide a favourable ionic diffusion environment in the bulk and significantly suppress gas release from the surface. The target material is achievable in delivering a discharge capacity as high as 301 mAh g(-1) with initial Coulombic efficiency of 93.2%. After 100 cycles, a reversible capacity of 300 mAh g(-1) still remains without any obvious decay in voltage. This study sheds light on the comprehensive design and control of oxygen activity in transition-metal-oxide systems for next-generation Li-ion batteries.

A general thermodynamic relation is proved to exist between the nucleation work and the nucleus size regardless of the model for the excess free energy of the nucleus. When this energy is supersaturation independent, the relation reads as follows: the number of atoms (or molecules) in the nucleus equals the derivative with minus sign of the nucleation work with respect to the supersaturation Δμ. It is shown that, experimentally, a reliable determination of the nucleus size is possible when data for the stationary nucleation rate J are plotted in coordinates kT ln J vs. Δμ (k is the Boltzmann constant and T is the absolute temperature). The slope of such an experimental curve gives information about the nucleus size independently of the kind of nucleation: classical or atomistic, homogeneous or heterogeneous, three dimensional or two dimensional, etc.

We prove a general theorem that relates the variation of the work of formation of the critical nucleus with chemical potential and the size and composition of the critical nucleus. Applications are made to multicomponent nucleation and to both isothermal and nonisothermal phase transformations. We show that the excess number of molecules and the excess entropy of the critical nucleus are thus accessible to experimental determination with the help of data for the dependence of the nucleation rate on supersaturation. The results derived do not rely on classical nucleation approximations and thus apply down to the smallest nuclei of a few molecules only.

Abstract Theoretical descriptions of static properties of polymer brushes are reviewed, with an emphasis on monodisperse macromolecules grafted to planar, cylindrical, or spherical substrates. Blob concepts and resulting scaling relations are outlined, and various versions of the self‐consistent field theory are summarized: the classical approximation and the strong stretching limit, as well as the lattice formulation. The physical justification of various inherent assumptions is discussed, and computer simulation results addressing the test of the validity of these approximations are reviewed. Also, alternative theories, such as the single chain mean field theory and the density functional theory, are briefly mentioned, and the main facts about the models used in the computer simulations are summarized. Both molecular dynamics and Monte Carlo simulations are described, the latter including lattice models and bead‐spring models in the continuum. Also extensions such as brush–brush interactions or nanoparticles inside of brushes as well as the solubility of free chains in brushes are briefly mentioned. Pertinent experimental results, though still somewhat scarce, are mentioned throughout and their consequences on the status of the theoretical understanding of polymer brushes is emphasized. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

The Front Cover picture shows the novel sodium/seawater rechargeable energy storage system, which can be considered as a hybrid between a battery and a fuel cell. The system comprises a positive seawater electrode (open to air) and a sealed negative tin-carbon (Sn–C) composite electrode in contact with environmental-friendly, highly stabile ionic liquid-based anolyte. The anode compartment is separated from the cathode compartment by the NASICON solid electrolyte. Upon electrochemical discharge, Na+ ions that are released from the Sn–C anode migrate through the anolyte and the solid electrolyte to reach the cathode compartment where they form sodium hydroxide with the reduction product of water and oxygen (from seawater). More details can be found in the Full Paper by Kim et al. on page 42 in Issue 1, 2016 (DOI: 10.1002/cssc.201501328).

Structural changes in Li 2 MnO 3 cathode material for rechargeable Li‐ion batteries are investigated during the first and 33 rd cycles. It is found that both the participation of oxygen anions in redox processes and Li + ‐H + exchange play an important role in the electrochemistry of Li 2 MnO 3 . During activation, oxygen removal from the material along with Li gives rise to the formation of a layered MnO 2 ‐type structure, while the presence of protons in the interslab region, as a result of electrolyte oxidation and Li + ‐H + exchange, alters the stacking sequence of oxygen layers. Li re‐insertion by exchanging already present protons reverts the stacking sequence of oxygen layers. The re‐lithiated structure closely resembles the parent Li 2 MnO 3 , except that it contains less Li and O. Mn 4+ ions remain electrochemically inactive at all times. Irreversible oxygen release occurs only during activation of the material in the first cycle. During subsequent cycles, electrochemical processes seem to involve unusual redox processes of oxygen anions of active material along with the repetitive, irreversible oxidation of electrolyte species. The deteriorating electrochemical performance of Li 2 MnO 3 upon cycling is attributed to the structural degradation caused by repetitive shearing of oxygen layers.

A comprehensive review of theoretical approaches to simulate plasmonic-active metallic nano-arrangements is given. Further, various fabrication methods based on bottom-up, self-organization and top-down techniques are introduced. Here, analytical approaches are discussed to investigate the optical properties of isotropic and non-magnetic spherical or spheroidal particles. Furthermore, numerical methods are introduced to research complex shaped structures. A huge variety of fabrication methods are reviewed, e.g. bottom-up preparation strategies for plasmonic nanostructures to generate metal colloids and core-shell particles as well as complex-shaped structures, self-organization as well as template-based methods and finally, top-down processes, e.g. electron beam lithography and its variants as well as nanoimprinting. The review article is aimed at beginners in the field of surface enhanced spectroscopy (SES) techniques and readers who have a general interest in theoretical modelling of plasmonic substrates for SES applications as well as in the fabrication of the desired structures based on methods of the current state of the art.

The exhaustive body of literature published in the last four years on the development and application of systems based on surface-enhanced Raman spectroscopy (SERS) combined with microfluidic devices demonstrates that this research field is a current hot topic. This synergy, also referred to as lab-on-a-chip SERS (LoC-SERS) or nano/micro-optofluidics SERS, has opened the door for new opportunities where both techniques can profit. On the one hand, SERS measurements are considerably improved because the processes previously performed on a large scale in the laboratory and prone to human error can now be carried out in nanoliter volumes in an automatic and reproducible manner; on the other hand, microfluidic platforms need detection methods able to sense in small volumes and therefore, SERS is ideal for this task. The present review not only aims to provide the reader an overview of the recent developments and advancements in this field, but it also addresses the key aspects of fundamental SERS theory that influence the interpretation of SERS spectra, as well as the challenges brought about by the experimental conditions and chemometric data analysis.

Platinized Cu, Ni, and Co deposits have been formed on glassy carbon (GC) electrode substrates by a two-step process, whereby a controlled amount of the transition metal was electrodeposited onto GC and subsequently partially exchanged for Pt upon immersion of the Cu/GC, Ni/GC, and Co/GC electrodes into a chloroplatinic acid solution. The spontaneous partial replacement of the transition metal by Pt resulted in Pt(Cu)/GC, Pt(Ni)/GC, and Pt(Co)/GC electrodes whose composition and depth profile were obtained by energy-dispersive spectrometry (EDS) and sputter-etch Auger electron spectroscopy (AES). Following electrochemical conditioning (involving electrode exposure to the oxygen and hydrogen evolution potential regimes), all deposits displayed typical Pt surface electrochemistry in acid solutions. Pt(Cu) catalysts exhibited enhanced electrocatalytic activity for methanol oxidation both during voltammetric and constant potential experiments. The behavior of Pt(Ni) and Pt(Co) depended on the method of assessment; in short-term voltammetric experiments, they were inferior to pure Pt, whereas in long-term constant potential experiments they outperformed it. The superior methanol oxidation activity of Pt(Cu) among all catalysts tested is interpreted in terms of the effect of Cu, Ni, and Co on methanol dissociative chemisorption and CO poison removal at/from the Pt surface.

First, the potential role of Raman-based techniques in biomedicine is introduced. Second, an overview about the instrumentation for spontaneous and coherent Raman scattering microscopic imaging is given with a focus of recent developments. Third, imaging strategies are summarized including sequential registration with laser scanning microscopes, line imaging and global or wide-field imaging. Finally, examples of biomedical applications are presented in the context of single cells, laser tweezers, tissue sections, biopsies and whole animals.

Lithium metal as an electrode material possesses a native surface film, which leads to a rough surface and this has a negative impact on the cycling behavior. A simple, fast, and reproducible technique is shown, which makes it possible to flatten and thin the native surface film of the lithium‐metal anode. Atomic force microscopy and scanning electron microscopy images are presented to verify the success of the method and X‐ray photoelectron spectroscopy measurements reveal that the chemical composition of the lithium surface is also changed. Furthermore, galvanostatic measurements indicate superior cycling behavior of the surface modified electrodes compared to the as‐received ones. These results demonstrate that the native surface film plays a key role in the application of lithium metal as an anode material for lithium‐metal batteries and that the shown surface modification method is an excellent tool to obtain better performing Li metal electrodes.

. This behavior is described by a negative effective transference number of Li, resulting in a negative contribution of Li ions to the overall conductivity. Li effective transference numbers are in the range of -0.04 to -0.02, depending on Li salt concentration and anion type. Transference numbers thus clearly deviate from apparent transference numbers estimated from diffusion coefficients, as an effect of a vehicular transport mechanism. This has important implications for the mechanism of Li mass transport in Li ion batteries as the drift of charged clusters has to be overcompensated by diffusive mass transport of neutral, Li-containing aggregates.

Macroscopic properties of aqueous β-lactoglobulin (BLG) foams and the molecular properties of BLG modified air-water interfaces as their major structural element were investigated with a unique combination of foam rheology measurements and interfacial sensitive methods such as sum-frequency generation and interfacial dilatational rheology. The molecular structure and protein-protein interactions at the air-water interface can be changed substantially with the solution pH and result in major changes in interfacial dilational and foam rheology. At a pH near the interfacial isoelectric point BLG molecules carry zero net charge and disordered multilayers with the highest interfacial dilatational elasticity are formed at the air-water interface. Increasing or decreasing the pH with respect to the isoelectric point leads to the formation of a BLG monolayer with repulsive electrostatic interactions among the adsorbed molecules which decrease the interfacial dilational elasticity. The latter molecular information does explain the behavior of BLG foams in our rheological studies, where in fact the highest apparent yield stresses and storage moduli are established with foams from electrolyte solutions with a pH close to the isoelectric point of BLG. At this pH the gas bubbles of the foam are stabilized by BLG multilayers with attractive intermolecular interactions at the ubiquitous air-water interfaces, while BLG layers with repulsive interactions decrease the apparent yield stress and storage moduli as stabilization of gas bubbles with a monolayer of BLG is less effective.

Recent years have seen tremendous improvement of our understanding of high resolution reachable in TERS experiments, forcing us to re-evaluate our understanding of the intrinsic limits of this field, but also exposing several inconsistencies. On the one hand, more and more recent experimental results have provided us with clear indications of spatial resolutions down to a few nanometres or even on the subnanometre scale. Moreover, lessons learned from recent theoretical investigations clearly support such high resolutions, and vice versa the obvious theoretical impossibility to evade high resolution from a purely plasmonic point of view. On the other hand, most of the published TERS results still, to date, claim a resolution on the order of tens of nanometres that would be somehow limited by the tip apex, a statement well accepted for the past 2 decades. Overall, this now leads the field to a fundamental question: how can this divergence be justified? The answer to this question brings up an equally critical one: how can this gap be bridged? This review aims at raising a fundamental discussion related to the resolution limits of tip-enhanced Raman spectroscopy, at revisiting our comprehension of the factors limiting it both from a theoretical and an experimental point of view and at providing indications on how to move the field ahead. It is our belief that a much deeper understanding of the real accessible lateral resolution in TERS and the practical factors that limit them will simultaneously help us to fully explore the potential of this technique for studying nanoscale features in organic, inorganic and biological systems, and also to improve both the reproducibility and the accuracy of routine TERS studies. A significant improvement of our comprehension of the accessible resolution in TERS is thus critical for a broad audience, even in certain contexts where high resolution TERS is not the desired outcome.

Author explains in detail the kinetics of corrosion processes and gives a thorough study of their thermodynamical problems. He points out the factors which have influence on electrochemical corrosion. He investigates the role of cathodic inclusions concerning corrosion process in alloys and at the same time emphasizes their practical importance. He examines the corrosion processes taking place in the metals’ passive state. Further, he describes the circumstances of the metals becoming transpassivated. Author sets up the electrochemical mechanism of soil corrosion of metals and points out the factors influencing soil corrosion. He also describes various cases of atmospheric corrosion, which can also be regarded as a sort of electrochemical corrosion. Finally, he investigates certain cases of corrosion taking place in melted metals. Author also gives a rational classification of corrosion control methods based on the electrochemical theory.

Abstract 'Epitaxy' means order in the relative orientation of identical crystals nucleated and grown on a large single-crystal face. Every crystal of the deposited material is oriented in such a way that there is coincidence of some vectors of its reciprocal lattice with vectors of the reciprocal lattice of the substrate surface. Depending on the length of the coincident vectors, one distinguishes between epitaxy of first order (coincidence of basis vectors), second order, and so on. In this paper, selected epitaxial systems (metals on metal, semiconductor and insulator substrates, semiconductors on semiconductors) are used to illustrate the influence of the lattice mismatch, interatomic forces and experimental parameters on the mode of film growth. The interaction across the epitaxial interface induces homogeneous strain in ultra-thin films and inhomogeneous strain in thicker deposits. The periodic strain is usually described in terms of misfit dislocations or static distortion waves, which are mobile at elevated temperature (misfit dislocations vibrate like interacting quasiparticles). Molecular dynamics studies suggest that a resonant coupling of the epitaxial film with an external field of appropriate frequency can result in a dramatic decrease of the misfit dislocations density. The growth of epitaxial films is an example of a first-order phase transition. As such the basic features of its thermodynamics and kinetics had been clarified long before it became of interest as a high technology. For this reason, 3 begins with a brief historical survey covering the classical results of Gibbs, Volmer, Stranski and Kaischew, Stranski and Krastanov. As with any small phase, the ultra-thin epitaxial films have a chemical potential that strongly depends on film thickness. This circumstance provides the thermodynamic basis for three modes of epitaxial growth: island growth, layer growth and their combination, namely islands growing on one or two completely built up monolayers. The mode of growth under near-to-equilibrium conditions can be predicted by a thermodynamic criterion based on an analysis of the μ(n) dependence, which accounts for both the interaction across the epitaxial interface and the strains in the film. The film morphology under far-from-equilibrium conditions can be predicted by a kinetic criterion based on an analysis of the surface transport arising from the thermodynamic driving force μ(n)- μ(n - 1).

When the nucleation of a stable crystalline phase directly in a supersaturated old phase is greatly retarded, the crystal nuclei might nucleate within faster-forming particles of an intermediate phase. Here we present a theoretical investigation of the kinetics of this two-step nucleation of crystals and derive general expressions for the time dependence of the number of crystals nucleated within the particles of the intermediate phase. The results reveal that crystal nucleation can be strongly delayed by the slow growth of the particles and/or by the slow nucleation of the crystals in them. Furthermore, the linear part of the time dependence of the number of nucleated crystals is determined by the formation rate of the intermediate particles. This is in contrast with the one-step nucleation of crystals when this linear part is determined by the rate of crystal nucleation directly in the old phase. Criteria are proposed for distinction between the one- and two-step nucleation mechanisms, based on the supersaturation dependence of the delay time for nucleation. The application of the theoretical approach to the analysis of experimental data on the nucleation of crystals and other ordered aggregates of protein and other soluble materials is discussed.

A thermodynamically consistent formula for the work W to form homogeneously a one-component gaseous, liquid, or solid nucleus is derived in the scope of the Gibbs theory of capillarity. This formula is applicable to nuclei constituted of whatever number of molecules, because it is valid in the entire range of conditions between the binodal and the spinodal (when such exists) of the nucleating system. Analysis is based on a newly introduced dividing surface called conservative, because its specific surface energy is independent of the nucleus size. The thermodynamically consistent formula for W accounts for the annulment of the nucleation work at the spinodal. For spinodal-unlimited systems it turns into the classical formula for W, thereby justifying the application of the latter to such systems even when the nuclei are of a few molecules only. It is shown that for systems with spinodal, classically, the nucleation rate is lower than that calculated with the aid of the thermodynamically consistent formula for W. The correction is practically only temperature-dependent and vanishes for spinodal-unlimited systems. Expressions are obtained for the excess or deficiency number Δn of molecules in the density fluctuation and for the number nC of molecules constituting the corresponding nucleus defined by the conservative dividing surface. These expressions are valid for any value of Δn and nC and reveal why, as found in experiments and computer simulations, the classical Gibbs–Thomson equation is able to predict the size of nuclei built up of less than a few tens of molecules. The general results are applied to homogeneous one-component nucleation of solids, liquids or gases under isothermal or isobaric conditions.

The structure and thermodynamic properties of a system of end-grafted flexible polymer chains grafted to a flat substrate and exposed to a solvent of variable quality are studied by molecular dynamics methods. The macromolecules are described by a coarse-grained bead-spring model, and the solvent molecules by pointlike particles, assuming Lennard-Jones-type interactions between pairs of monomers (epsilon(pp)), solvent molecules (epsilon(ss)), and solvent monomer (epsilon(ps)), respectively. Varying the grafting density sigma(g) and some of these energy parameters, we obtain density profiles of solvent particles and monomers, study structural properties of the chain (gyration radius components, bond orientational parameters, etc.), and examine also the profile of the lateral pressure P( parallel)(z), keeping in the simulation the normal pressure P( perpendicular) constant. From these data, the reduction of the surface tension between solvent and wall as a function of the grafting density of the brush has been obtained. Further results include the stretching force on the monomer adjacent to the grafting site and its variation with solvent quality and grafting density, and dynamic characteristics such as mobility profiles and chain relaxation times. Possible phase transitions (vertical phase separation of the solvent versus lateral segregation of the polymers into "clusters," etc.) are discussed, and a comparison to previous work using implicit solvent models is made. The variation of the brush height and the interfacial width of the transition zone between the pure solvent and the brush agrees qualitatively very well with corresponding experiments.

Abstract A nonenzymatic electrochemical sensor for detection of sugars was prepared by layer‐by‐layer deposition of gold nanoparticles on thin gold electrodes. The deposition was optimized by using of surface plasmon resonance. Voltammetric investigation and impedance spectroscopy of the sensor was performed. Electrical currents caused by glucose on bare gold electrodes and on gold electrodes coated by immobilized gold nanoparticles were compared. The electrodes with nanoparticles display much higher current of glucose oxidation. The oxidation becomes blocked when the swept electrode potential exceeded +0.25 V, during the back scan an oxidation peak is observed again but at less positive potential. The magnitudes of these current peaks are linearly dependent on the glucose concentration; this dependence can be used as calibration for analytical applications. The limit of detection for glucose is below 0.5 mM, the sensitivity (normalized to the macroscopic electrode surface) is about 160 μA cm −2 mM −1 . The sensor response is linear till at least 8 mM of glucose concentration.