Influence Of Lateral Interactions Research Articles

Quantitative Effects of Disorder on Chemically Modified Amorphous Carbon Electrodes.

Real materials are disordered. This disorder influences the properties of these materials and the chemical processes that occur at their interfaces. Gaining a molecular-level understanding of the underlying physical manifestations caused by disordered materials is crucial to unraveling and ultimately controlling the efficiency and performance of these materials in a range of energy-related devices. This understanding necessitates measurement techniques through which disorder can be detected, quantified, and monitored. However, such quantitative measurements are notoriously difficult, as effects often average out in ensemble measurements. In this work, we describe how a combination of electrochemical and spatially resolved surface spectroscopy measurements illuminate a molecular-level picture of disorder in materials. Using amorphous carbon as an intrinsically disordered material, we covalently attached a monolayer of ferrocene. Interfacial electron transfer across the amorphous carbon-ferrocene interface is highly sensitive to disruptions of order. By systematically varying linker properties and surface loadings, the influence of lateral interactions between nonuniformly distributed ferrocene headgroups on ensemble electrochemical measurements is demonstrated. Electrochemical and imaging data collectively indicate that conformational flexibility of the ferrocene moieties provides a mechanism to elude repulsive and unbalanced lateral interactions, while rigid linkages provide direct information about the underlying disorder of the material. This study is the first of its kind to quantify and visualize molecular disorder and heterogeneity with an experimental model accessed through ensemble measurements.

Lateral Interactions Influence the Kinetics of Metastable Pores in Lipid Membranes

The formation of through pores in lipid bilayer membranes occurs in a number of cellular processes and is also applied for biotechnological and biomedical purposes. In the classical theory of pore formation, diffusion of membrane defects in space of radii is considered. When the first pore reaches a critical radius, the membrane irreversibly ruptures. It is usually presumed that the diffusion of defects occurs independently; their possible lateral interactions are not taken into account. In this paper, we consider a possible influence of lateral interactions of metastable through pores on their kinetics. It is assumed that the interaction occurs due to the overlap of elastic deformation fields arising at the edges of two pores. The interaction energy of two circular pores was calculated in the Derjaguin approximation for rapidly decaying potentials. The unidimensional potential of interaction of two linear parallel edges of pores formed in membranes of different lipid composition was calculated in the framework of the theory of elasticity of liquid crystals adapted to lipid membranes. It is shown that this interaction should lead to a considerable reduction of the measured line tension of the pore edge. In addition, the lifetime of two optimally situated metastable pores can increase approximately 10 times due to the interaction. Extrapolation of the obtained results to the case of a larger number of interacting pores makes it possible to predict an additional increase in the lifetime by one or two orders of magnitude.

Isotherms, kinetics and thermodynamics for adsorption of pyridine vapors on modified activated carbons

The adsorption isotherms of pyridine have been determined gravimetrically on different samples of granulated, fibrous and spherical activated carbons. Several chemical treatments such as oxidation, degassing and impregnation have been carried out on as-received activated carbon cloth (ACC) so as to modify the surface characteristics of the activated carbon. The porous and chemical structure of modified and unmodified activated carbons has been characterised by XRD, TGA–DTG, SEM and pore size distribution techniques. The adsorption increases on oxidation while decreases on degassing which can be correlated to increase and decrease in the concentration of surface oxygen groups. Loading with Ag+ and Cu2+ increases the adsorption of pyridine compared with the unloaded sample while loading with Cr6+ decreases the adsorption of these vapors. The adsorption–desorption branches of pyridine vapors on metal impregnated do not meet even at zero relative vapor pressure indicating the chemisorption or other specific interactions. The adsorption kinetics data has been examined using the linear driving force and empirical diffusion models. The initial decrease in isosteric enthalpy of adsorption for modified and unmodified ACC indicates the effect of surface heterogeneity and later increase indicates the influence of lateral interactions between adsorbate molecules. The results suggest that the adsorption of pyridine involves the physisorption as well as specific interactions with carbon oxygen functional groups and metal complexes present on the carbon surface.

Gas Transport in Bidisperse Coal Particles: Investigation for an Effective Diffusion Coefficient in Coalbeds

Abstract Much work has been carried out on adsorption capacity of coals. Diffusive transport processes within the coal matrix blocks could be the rate-limiting step for adsorption during gas injection and production operations. Identifying these processes and determining their contributions to overall mass transport is a complex and time consuming procedure. The paper presents numerical diffusion models in varying coal particles and investigates transport mechanisms. For this purpose, the coal particle is represented as a microporous solid penetrated by a network of larger interconnected macropores. The solid adsorbs the bulk of the gas. A simple relationship between the apparent and intrinsic Fickian diffusion coefficients is derived in the case of single-component (methane) transport and Langmuir-type adsorption. Mass transport in the bidisperse coal particle is significantly influenced by the adsorption in the microporous solid. The investigation is then extended to study concentration dependence of the microporous solid diffusion for binary (methane-CO2) mixtures using the Maxwell-Stefan formulation. It is found that co-diffusion of the gas molecules enhances the gas mass transport in the solid in the presence of competitive sorption dynamics, while counter-diffusion may diminish the gas mass transport. The influence of lateral interactions among the adsorbed molecules in the solid phase is discussed. The work finds application in modelling CBM and CO2-ECBM processes. Introduction As an unconventional natural gas resource, coalbed methane receives worldwide attention. Deep coal seams that are not accessible for mining are suitable for in situ gas production using conventional drilling, well completion and gas recovery technologies. Hence, a vast amount of natural gas is globally available. Unlike conventional gas resources, however, the gas storage, flow and transport processes in coalbeds are quite complex mainly due to the intricate nature of coal(1–6). Coalbeds are porous media often characterized by a bimodal pore structure: a primary structure consisting of micro- and meso-scale pores, and a secondary structure with macropores and interconnected natural fractures. The microporous coal has an extremely large internal surface area and a strong affinity for certain naturally occurring chemical species such as methane, carbon dioxide, nitrogen and water. At high coalbed pressures, therefore the majority of the natural gas-in-place, in particular, methane, exists abundantly at an adsorbed liquid-like state in the microporous solid(1). Depressurizing the coalbed may yield a significant volume of natural gas. However, the initial stage of recovery is often dominated by water production, whereas, the latter stage is under the influence of diffusional resistances of the primary pores of the coal matrix. Treatment and disposal of the produced water is expensive and its long-term environmental impact has not been clearly understood yet. Injection of a second gas with much higher adsorption capacity, on the other hand, could possibly enhance recovery by maintaining the overall reservoir pressure, thus, keeping the water production at a minimum level. Additionally, injecting a second gas would promote methane desorption by lowering the partial pressure of the coalbed methane in the migrating gas phase.

Monte Carlo simulations of controlled rate thermal analysis spectraThe influence of surface energetic heterogeneity and lateral interactions between adsorbed molecules

Monte Carlo simulations of controlled rate thermal analysis (CRTA) spectra are presented. Calculations are performed for a few kinds of energetically heterogeneous surface, characterized by symmetrical and unsymmetrical desorption energy distributions. It is shown that the shape of the CRTA spectra corresponds with the shape of integral form of desorption energy distribution on the surface. A simple way of estimation of the upper limit of desorption energy is proposed. The influence of lateral interactions on the shape of the CRTA spectra is also discussed. It is stated that strong attractive interactions cause the desorption temperature to be constant. As a result of repulsive interactions two steps on the desorption temperature curve are observed. For the case of repulsive interactions between the nearest-neighbors and next-nearest-neighbors the CRTA spectra do not reveal the existence of multiple steps, contrary to the classical thermodesorption spectra (TPD) where, in such a case, multiple peaks are observed.

Monte Carlo simulations of controlled rate thermal analysis spectra: The influence of surface energetic heterogeneity and lateral interactions between adsorbed molecules

Monte Carlo simulations of controlled rate thermal analysis (CRTA) spectra are presented. Calculations are performed for a few kinds of energetically heterogeneous surface, characterized by symmetrical and unsymmetrical desorption energy distributions. It is shown that the shape of the CRTA spectra corresponds with the shape of integral form of desorption energy distribution on the surface. A simple way of estimation of the upper limit of desorption energy is proposed. The influence of lateral interactions on the shape of the CRTA spectra is also discussed. It is stated that strong attractive interactions cause the desorption temperature to be constant. As a result of repulsive interactions two steps on the desorption temperature curve are observed. For the case of repulsive interactions between the nearest-neighbors and next-nearest-neighbors the CRTA spectra do not reveal the existence of multiple steps, contrary to the classical thermodesorption spectra (TPD) where, in such a case, multiple peaks are observed.

The Influence of Lateral Interactions between Adsorbed Molecules on Adsorption Kinetics. A Statistical Rate Theory Approach

The influence of lateral interactions between the adsorbed molecules is studied using the statistical rate theory (SRT). This approach makes it possible to introduce the interaction term into the kinetic equation in an easy and thermodynamically consistent way. The quasi-chemical approximation was applied to calculate the chemical potential of adsorbed molecules. The short-time behavior of the kinetic equation based on SRT is in agreement with experimental findings for the systems with lateral interactions. Moreover, the long-term behavior agrees with the equilibrium Langmuir isotherm combined with the quasi-chemical approximation. The experimental system, CO adsorption on Rh(100), was used for quantitative analysis; as a result, a good simultaneous description of equilibria and kinetics in this system was obtained.

The influence of lateral interactions on surface pyrolysis of silicon hydrides

In this paper features of disintegration of silicon hydrides on Si(100) surface are considered. The simulation of hydrogen TPD-spectra has shown that there are three ways for hydrogen desorbtion and that disintegration of molecules SiH2 proceeds through bimolecular reactions only. The comparison of calculations and experiments allowed to estimate kinetic constants of elementary reactions of pyrolysis.

Influence of lateral interactions on Raman scattering by molecules adsorbed on a solid surface: a model study

This article presents results of theoretical description and numerical modeling of processes like Raman scattering by molecular layers obtained with account of lateral interactions in such layers. Green functions for a half-space with an ultra-thin film is obtained from a self-consistent Dyson equation. Expression for the response of such a system on shifted frequency, which has straightforward physical interpretation, is given. It is shown that lateral interactions create new modes localized on the ultra-thin film and it is the interaction with these modes, which can enhance response of such a film in different processes. Numerical calculations based on the presented theoretical results exhibit the possibility to enhance Raman scattering by adsorbed molecules both for p- and s-polarized light. Detailed qualitative analysis of these processes clearly demonstrates that enhancement may be reached just by interaction with discussed modes. Obtained enhancement is not giant for Raman scattering, but it is remarkable and can be reached for any light polarization and for bigger variety of systems than surface enhanced Raman scattering can.

The influence of lateral interactions on the anglular distribution in photodesorption

Photodesorption and photodissocn. are induced when O2 adsorbed on Pd (111) is irradiated with UV light. Both processes are nonthermal. Thermal desorption of mol. O is obsd. as a consequence of a displacement process by the nascent at. O. Angle-resolved time-of-flight spectra were recorded. For the adsorbed mol. superoxo species, these measurements show a pronounced translational energy max. at a desorption angle of 60 Deg. Also, this peak is only obsd. at certain azimuthal angles indicating C3v symmetry.

The influence of lateral interactions on the angular distribution in photodesorption

Photodesorption and photodissociation are induced when O 2 adsorbed on Pd(111) is irradiated with UV light. Both processes are non-thermal. In addition thermal desorption of molecular oxygen is observed as a consequence of a displacement process by the nascent atomic oxygen. Angle-resolved time-of-flight spectra were recorded. For the adsorbed molecular superoxo species these measurements show a pronounced maximum in the translational energy at a desorption angle of 60°. Moreover, this peak is only observed at certain azimuthai angles indicating C 3v symmetry.

The influence of lateral interactions on the critical behavior of a dimer–monomer surface reaction model

The ZGB model [Ziff et al., Phys. Rev. Lett. 56, 2553 (1986)] for a monomer–dimer surface reaction process of the type A+(1/2)B2→AB, exhibits two irreversible phase transitions (IPT) from a stationary regime with AB production for p1A≤pA≤p2A, to poisoned states with B (A)-species for pA≤p1A (pA≥p2A), respectively, where pA is the mole fraction of A-species in the gas phase and piA (i=1, 2) are critical points. A generalization of the ZGB model in order to account for both attractive and repulsive interactions between the reactants is presented and discussed. It is found that in most cases the first order IPT at p2A becomes of second order and the critical points are shifted. For some particular choices of the interactions energies it is found that the second order IPT at p1A becomes of first order. Also, a first order IPT from the reactive state to a effectively poisoned regime where A-species are adsorbed forming a c(2×2) metastable structure is obtained.

Geometric effects in the control of catalytic selectivity by surface additives: Monte Carlo simulation studies

The influence of lateral interactions between adspecies on a metal surface in the occurrence of “ensemble” and “electronic” effects in chemisorption and catalysis has been examined using Monte Carlo simulation method. The lateral forces are limited to pairwise interactions ( E ) of magnitide −5 (atractive) E ≤10 kJ mol −1 (repulsive) between poison species in adjacent sites. The variations in extent of chemisorption of “probe” molecules exhibiting critical ensemble sizes of three, seven and thirteen are evaluated as a function of E and poison coverage; the dependence on these variables of the concentration of electronically perturbed sites is also discussed. The general observation is that the results are rather sensitive to the value of E , suggesting that variations in lateral interactions may play a significant role in explaining the differing catalytic influences of particular surface additives. Multiple domain occupancy is shown to affect the standard procedure used to determine ensemble sizes from selective chemisorption measurements and phenomena relating to the fluid − 3 × 3 R 30 ° phase transition in the poison lattice are described.

The influence of lateral interactions in the occurrence of ensemble effects in chemisorption and catalysis

The influence of lateral interactions in the occurrence of ensemble effects in chemisorption and catalysis

Lattice-gas model of bimolecular reaction on surface

A lattice-gas model and absolute rate theory are used to describe the influence of lateral interactions on the Langmuir-Hinshelwood bimolecular reaction on a surface. The rate of the reaction is expressed through the probabilities of distribution of particles on the surface. These probabilities are calculated in the quasi-chemical approximation. Results indicate that the rate of reaction strongly depends on surface coverages and on the surface structure already when interaction energies approximately equal kT.

Surface diffusion of adsorbed species: A review

Advances made in the study of the diffusion of adsorbed species on single crystal surfaces are summarized. An appraisal of the techniques and methods of data treatment which have been developed for both macroscopic (single crystals cut to expose a given crystal plane) and microscopic (field emitter) surfaces is presented, and a brief survey is made of the data obtained for precursor, molecularly chemisorbed, and dissociatively chemisorbed states. The influence of lateral interactions between adatoms on diffusion parameters is explicitly examined in relation to recent results for O adatoms on W{110}. Finally, a brief survey is given of the importance of diffusion in other surfaces processes, such as the formation of ordered overlayers and adsorption and desorption kinetics.

The influence of lateral interactions on the vibrational spectrum of adsorbed CO

Vibrational spectroscopy of adsorbed CO often reveals strong shifts of the CO stretch absorption band to higher frequencies as a function of increasing coverage. It is shown that such shifts are due essentially to dipole-dipole interactions. The extent of the experimentally observed effect can, however, only be reproduced when screening by the substrate is taken into account properly.