HAS Research Group of Technical Analytical Chemistry

Budapest, Hungary

HAS Research Group of Technical Analytical Chemistry

Budapest, Hungary

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Szoori M.,University of Szeged | Roeselova M.,Czech Institute of Organic Chemistry And Biochemistry | Jedlovszky P.,Eötvös Loránd University | Jedlovszky P.,HAS Research Group of Technical Analytical Chemistry
Journal of Physical Chemistry C | Year: 2011

Grand Canonical Monte Carlo (GCMC) simulations are used to study the adsorption and organization of gas-phase water molecules on two-component self-assembled monolayers (SAMs) of eight-carbon alkanethiols bound to a flat virtual carrier, as the character of the SAM surface is changing from completely hydrophobic to completely hydrophilic by randomly replacing methyl-terminated (C7-CH3) alkanethiol chains with carboxylic acid-terminated (C7-COOH) chains. At low chemical potentials (low relative humidity), a synergistic effect of nearby COOH functional groups on water adsorption is observed. In particular, clusters of nearby surface COOH groups are found to attract considerably more water molecules than the same amount of COOH groups if they are isolated from each other. By promoting lateral water-water interactions, such surface COOH clusters thus act as condensation nuclei for water. With increasing water chemical potential, the possibility of the formation of new water-water hydrogen bonds gradually becomes an increasingly important driving force of the adsorption, in addition to the formation of new water-COOH hydrogen bonds. Further, as the relative humidity increases, the growing number of water-water hydrogen bonds clearly overcompensates the effect of the decreasing average number of water-COOH hydrogen bonds per (first layer) water molecules. These findings are supported by the adsorption isotherms, by the preferential orientation of the surface COOH groups and first layer water molecules, and by the binding energy distributions of the water molecules being in direct contact with the SAM surface as obtained from the simulation. The atmospheric relevance of our results is also considered. © 2011 American Chemical Society.


Szri M.,University of Szeged | Szri M.,Czech Institute of Organic Chemistry And Biochemistry | Jedlovszky P.,Eötvös Loránd University | Jedlovszky P.,HAS Research Group of Technical Analytical Chemistry | Roeselova M.,Czech Institute of Organic Chemistry And Biochemistry
Physical Chemistry Chemical Physics | Year: 2010

Grand canonical Monte Carlo simulations are used to determine water adsorption on prototypical organic surfaces as a function of relative humidity at 300 K. Three model surfaces formed by well-ordered self-assembled monolayers (SAMs) of alkanethiolate chains on gold are investigated: (i) a smooth hydrophobic surface of methyl-terminated C7-CH3 SAM; (ii) a rough hydrophobic surface of randomly mixed two-component SAM, composed of equal fractions of C5-CH3 and C7-CH3 chains (C5/C7-CH3 SAM); and (iii) a smooth hydrophilic surface of carboxyl-terminated C7-COOH SAM. The all atom CHARMM22 force field is used for the SAM chains together with the SPC/E model for water. No noticeable water adsorption is observed on the smooth hydrophobic surface up to saturation. The mild surface roughness introduced by the uneven chain length of the two components constituting the C5/C 7-CH3 SAM has no significant effect on the surface hydrophobicity, and the rough hydrophobic surface also remains dry up to the point when water condensation occurs. In contrast, water readily adsorbs onto the hydrophilic surface by forming hydrogen bonds with the COOH groups of the substrate. In addition, hydrogen bonding with pre-adsorbed water molecules contributes to the mechanism of water uptake. Under low humidity conditions, water is present on the hydrophilic surface as individual molecules or small water clusters and, with increasing relative humidity, the surface coverage grows continuously beyond a monolayer formation. The adsorbed water film is observed to be rather inhomogeneous with patches of bare surface exposed. The amount of water constituting a stable adsorption layer prior to condensation is estimated to consist of about 2-5 molecular layers. Detailed analysis of the simulation results is used to obtain important insights into the structure and energetics of water adsorbed on highly oxidized organic surfaces exposed to ambient air of increasing relative humidity. © the Owner Societies.


Pojjak K.,Eötvös Loránd University | Darvas M.,Eötvös Loránd University | Darvas M.,University of Franche Comte | Horvai G.,HAS Research Group of Technical Analytical Chemistry | And 3 more authors.
Journal of Physical Chemistry C | Year: 2010

Molecular dynamics simulations of the liquid-vapor interface of water-dimethyl sulfoxide (DMSO) mixtures of nine different compositions, ranging from neat water to neat DMSO, are performed on the canonical (N,V,T) ensemble at 298 K. The surface molecular layer of the systems are identified and analyzed in detail in terms of the novel identification of the truly interfacial molecules (ITIM) method. The obtained results show that DMSO is adsorbed at the surface of such mixtures at every composition, but this adsorption is limited solely to the first molecular layer beneath the surface. Within the surface layer the minor component is always found to be preferentially located at the outer edge of the layer, close to the vapor phase. The preferred orientations of both molecules at the surface of their neat liquids are such that they can prevail upon addition of the other component, and the unlike molecules can form strong hydrogen bonds with each other in their preferred orientations. Thus, neither the water nor the DMSO molecules perturb considerably the local surface structure of the other component. On the other hand, similarly to the bulk liquid phase the like components show self-association behavior also at the surface of the mixed systems. Further, the lateral percolating hydrogen-bonding network of the surface water molecules, present at the surface of neat liquid water, is found to be broken already at the bulk phase DMSO concentration of 3.3 mol % (corresponding to the surface DMSO concentration of 25 mol %). This breakdown of the lateral percolating network of surface waters is found to be accompanied by a sudden increase of the mobility of the water molecules between the surface layer and the bulk-like part of the system. © 2010 American Chemical Society.


Darvas M.,University of Franche Comte | Darvas M.,Eötvös Loránd University | Lasne J.,University Pierre and Marie Curie | Laffon C.,University Pierre and Marie Curie | And 4 more authors.
Langmuir | Year: 2012

Detailed investigation of the adsorption of acetaldehyde on I h ice is performed under tropospheric conditions by means of grand canonical Monte Carlo computer simulations and compared to infrared spectroscopy measurements. The experimental and simulation results are in a clear accordance with each other. The simulations indicate that the adsorption process follows Langmuir behavior in the entire pressure range of the vapor phase of acetaldehyde. Further, it was found that the adsorption layer is strictly monomolecular, and the adsorbed acetaldehyde molecules are bound to the ice surface by only one hydrogen bond, typically formed with the dangling H atoms at the ice surface, in agreement with the experimental results. Besides this hydrogen bonding, at high surface coverages dipolar attraction between neighboring acetaldehyde molecules also contributes considerably to the energy gain of the adsorption. The acetaldehyde molecules adopt strongly tilted orientations relative to the ice surface, the tilt angle being scattered between 50° and 90° (i.e., perpendicular orientation). The range of the preferred tilt angles narrows, and the preference for perpendicular orientation becomes stronger upon saturation of the adsorption layer. The CH 3 group of the acetaldehyde molecules points as straight away from the ice surface within the constraint imposed by the tilt angle adopted by the molecule as possible. The heat of adsorption at infinitely low coverage is found to be -36 ± 2 kJ/mol from the infrared spectroscopy measurement, which is in excellent agreement with the computer simulation value of -34.1 kJ/mol. © 2012 American Chemical Society.


Partay L.B.,University of Cambridge | Horvai G.,HAS Research Group of Technical Analytical Chemistry | Horvai G.,Budapest University of Technology and Economics | Jedlovszky P.,HAS Research Group of Technical Analytical Chemistry | Jedlovszky P.,Eötvös Loránd University
Journal of Physical Chemistry C | Year: 2010

The properties of the interface between water and benzene are investigated in detail on the basis of 23 Monte Carlo computer simulations performed at various temperatures and pressures. The interfacial properties are analyzed in terms of the novel identification of the truly interfacial molecules (ITIM) method, by which the intrinsic (i.e., capillary wave corrugated) surface of the two phases can be detected. The obtained results show that the use of a simple, nonintrinsic definition of the interface (made on the basis of the average density profiles of the components) not only leads to a systematic error in determining the list of the truly interfacial molecules, but this error is also reflected in the erroneous calculation of the thermodynamic properties of the system. The obtained results show that the reciprocal width and reciprocal amplitude of both surface layers decrease linearly with the temperature and reach the value of zero (i.e., the corresponding parameters become infinite) at the point of mixing of the two phases. Similar linear relation is observed between these reciprocal quantities and the logarithm of the pressure, but only above a certain temperature. This temperature is thought to be the upper end of the lower critical line of the phase diagram of the system; however, any reliable support of this conjecture would require a considerably larger number of simulations in the temperature range close to this line. The orientational preferences of the surface water molecules, governed by the principle of maximizing the number of their hydrogen-bonded neighbors, are found to be insensitive to the thermodynamic conditions but become weaker with increasing temperature and decreasing pressure. The lateral hydrogen-bonding network of the surface water molecules, spanning the entire water surface at ambient conditions, is found to undergo a percolation transition well, i.e., 200-400 K below the mixing of the two phases, indicating that the existence of such a percolating lateral network is not a universal feature of the water surface but depends also on the thermodynamic conditions. © 2010 American Chemical Society.


Darvas M.,University of Franche Comte | Darvas M.,Eötvös Loránd University | Picaud S.,University of Franche Comte | Jedlovszky P.,Eötvös Loránd University | Jedlovszky P.,HAS Research Group of Technical Analytical Chemistry
Physical Chemistry Chemical Physics | Year: 2011

The phase behaviour of binary oxalic acid-water mixtures has been investigated by means of computer simulation techniques. Such mixtures play an important role in atmospheric processes, since the hydrogen bonding ability of oxalic acid molecules allows them to form aerosol particles. Water can in turn be readily adsorbed on the surface of such aerosol particles, which results in the formation of small ice grains. These grains are thus considered to be acting as cloud condensation nuclei, giving rise to the formation of ice clouds. © the Owner Societies 2011.


Idrissi A.,Lille University of Science and Technology | Vyalov I.,Lille University of Science and Technology | Vyalov I.,RAS Institute of Chemistry | Kiselev M.,RAS Institute of Chemistry | And 2 more authors.
Physical Chemistry Chemical Physics | Year: 2011

Binary mixtures of CO2 with ethanol and with acetone are studied by computer simulation, including extensive free energy calculations done by the method of thermodynamic integration, at 313 K, i.e., above the critical point of CO2 in the entire composition range. The calculations are repeated with three different models of acetone and ethanol, and two models of CO2. Comparisons of the molar volume of the different systems as well as of the change of their molar volume accompanying the mixing of the two components with experimental data reveal that, among the model pairs tested, the best results are obtained if both components are described by the Transferable Potentials for Phase Equilibria (TraPPE) force field. Around the ethanol/acetone mole fraction of 0.05 all ethanol/CO2 and almost all acetone/CO 2 model pairs considered predict the existence of a sharp maximum of the molar volume. Due to the lack of experimental data in this composition range, however, these predictions cannot be verified/falsified yet. Most of the model pairs considered also predict limited miscibility of these compounds, as seen from the positive values of the free energy change accompanying their mixing, and the miscibility gap is located at the same composition range as the aforementioned molar volume maximum. © 2011 the Owner Societies.


Darvas M.,Eötvös Loránd University | Darvas M.,University of Franche Comte | Gilanyi T.,Eötvös Loránd University | Jedlovszky P.,Eötvös Loránd University | Jedlovszky P.,HAS Research Group of Technical Analytical Chemistry
Journal of Physical Chemistry B | Year: 2011

Competitive adsorption of a neutral amphiphilic polymer, namely poly(ethylene oxide) (PEO) and an ionic surfactant, i.e., sodium dodecyl sulfate (SDS), is investigated at the free water surface by computer simulation methods at 298 K. The sampled equilibrium configurations are analyzed in terms of the novel identification of the truly interfacial molecules (ITIM) method, by which the intrinsic surface of the aqueous phase (i.e., its real surface corrugated by the capillary waves) instead of an ideally flat surface approximating its macroscopic surface plane, can be taken into account. In the simulations, the surface density of SDS is gradually increased from zero up to saturation, and the structural, dynamical, and energetic aspects of the gradual squeezing out of the PEO chains from the surface are analyzed in detail. The obtained results reveal that this squeezing out occurs in a rather intricate way. Thus, in the presence of a moderate amount of SDS the majority of the PEO monomer units, forming long bulk phase loops in the absence of SDS, are attracted to the surface of the solution. This synergistic effect of SDS of moderate surface density on the adsorption of PEO is explained by two factors, namely by the electrostatic attraction between the ionic groups of the surfactant and the moderately polar monomer units of the polymer, and by the increase of the conformational entropy of the polymer chain in the presence of the surfactant. This latter effect, thought to be the dominant one among the above two factors, also implies the formation of similar polymer/surfactant complexes at the interface than what are known to exist in the bulk phase of the solution. Finally, in the presence of a large amount of SDS the more surface active surfactant molecules gradually replace the PEO monomer units at the interfacial positions, and squeezing out the PEO molecules from the surface in a monomer unit by monomer unit manner. © 2011 American Chemical Society.


Jorge M.,University of Porto | Jedlovszky P.,Eötvös Loránd University | Jedlovszky P.,HAS Research Group of Technical Analytical Chemistry | Cordeiro M.N.D.S.,University of Porto
Journal of Physical Chemistry C | Year: 2010

Substantial progress in our understanding of interfacial structure and dynamics has stemmed from the recent development of algorithms that allow for an intrinsic analysis of fluid interfaces. These work by identifying the instantaneous location of the interface, at the atomic level, for each molecular configuration and then computing properties relative to this location. Such a procedure eliminates the broadening of the interface caused by capillary waves and reveals the underlying features of the system. However, a precise definition of which molecules actually belong to the interfacial layer is difficult to achieve in practice. Furthermore, it is not known if the different intrinsic analysis methods are consistent with each other and yield similar results for the interfacial properties. In this paper, we carry out a systematic and detailed comparison of the available methods for intrinsic analysis of fluid interfaces, based on a molecular dynamics simulation of the interface between liquid water and carbon tetrachloride. We critically assess the advantages and shortcomings of each method, based on reliability, robustness, and speed of computation, and establish consistent criteria for determining which molecules belong to the surface layer. We believe this will significantly contribute to make intrinsic analysis methods widely and routinely applicable to interfacial systems. © 2010 American Chemical Society.


Darvas M.,Eötvös Loránd University | Darvas M.,University of Franche Comte | Gilanyi T.,Eötvös Loránd University | Jedlovszky P.,Eötvös Loránd University | Jedlovszky P.,HAS Research Group of Technical Analytical Chemistry
Journal of Physical Chemistry B | Year: 2010

Molecular dynamics simulation of poly(ethylene oxide) (PEO) adsorbed at the free water surface are reported on the canonical ensemble at 298 K. The obtained results are analyzed in terms of the novel Identification of the Truly Interfacial Molecules (ITIM) method. To obtain a deep, molecular level insight into the origin of the adsorption process, structural, dynamical, and energetic aspects have been investigated. It is found that the vast majority, i.e., 82%, of the monomer units of PEO are immersed into the bulk liquid phase, 17% of them are anchored right at the liquid-vapor interface, while 1% of them penetrate into the vapor phase. Although the presence of a few monomer units in the vapor phase is clearly demonstrated, the average lifetime of these monomer units is found to be rather small, i.e., 3.1 ps, and they are found not to move far from the surface as their interaction energy with the water molecules is still not negligible. The partition of the monomer units between the bulk liquid phase, interface, and vapor phase is determined by the delicate interplay of entropic and energetic factors, mostly by the requirements of maximizing the configurational entropy of the polymeric chain and minimizing the interfacial energy surplus. © 2010 American Chemical Society.

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