Molecular Characterization of the Surface Excess Charge Layer in Droplets

2020 ◽  
Author(s):  
Victor Kwan ◽  
Styliani Consta
Keyword(s):  
Hydrogen Bonds ◽  
Droplet Size ◽  
Atmospheric Aerosols ◽  
Negative Ions ◽  
Total Charge ◽  
Excess Charge ◽  
Surface Excess ◽  
High Concentration ◽  
Dipole Orientation ◽  
Charge Layer

Charged droplets play a central role in native mass spectrometry, atmospheric aerosols and in serving as micro-reactors for accelerating chemical reactions. The surface excess charge layer in droplets has often been associated with distinct chemistry. Using molecular simulations we have found that this layer is ≈ 1.5−1.7 nm thick and depending on the droplet size it includes 33%-55% of the total number of ions. Here, we examine the effect of droplet size and sign of ions in the structure of the surface excess charge layer by using molecular dynamics. We find that the thickness of the surface excess charge layer is invariant not only with respect to droplet size but also with respect to the nature of the ions and it is not sensitive to fine details of different force fields used in our simulations. We also find that differences in the average water dipole orientation in the presence of positive and negative ions in this layer are reflected in the charge distributions. Within the surface charge layer, the number of hydrogen bonds reduces gradually relative to the droplet interior where the number of hydrogen bonds is on the average 2.9 for droplets of diameter < 4 nm and 3.5 for larger droplets. The decrease in the number of hydrogen bonds from the interior to the surface is less pronounced in larger droplets. In droplets with diameter < 4 nm and high concentration of ions the charge of the ions is not compensated only by the solvent polarization charge but by the total charge that also includes the other free charge. This finding shows exceptions to the commonly made assumption that the solvent “neutralizes” the charge of the ions in solvents with very high dielectric constant. The simulation findings provide molecular insight into the bi-layer droplet structure assumed in the equilibrium partitioning model of C. Enke.<br>

Molecular Characterization of the Surface Excess Charge Layer in Droplets

2020 ◽  
Author(s):  
Victor Kwan ◽  
Styliani Consta
Keyword(s):  
Hydrogen Bonds ◽  
Surface Charge ◽  
Droplet Size ◽  
Chloride Ions ◽  
Total Charge ◽  
Excess Charge ◽  
Surface Excess ◽  
High Concentration ◽  
Dipole Orientation ◽  
Charge Layer

<div>Charged droplets play a central role in native mass spectrometry, atmospheric aerosols and in serving as micro-reactors for accelerating chemical reactions. The surface excess charge layer in droplets has often been associated with distinct chemistry. Using molecular simulations for droplets with Na+ and Cl- ions we have found that this layer is ≈ 1.5−1.7 nm thick and depending on the droplet size it includes 33%-55% of the total number of ions. Here, we examine the effect of droplet size and nature of ions in the structure of the surface excess charge layer by using molecular dynamics. We find that in the presence of simple ions the thickness of the surface excess charge layer is invariant not only with respect to droplet size but also with respect to the nature of the simple ions and it is not sensitive to fine details of different force fields used in our simulations.</div><div> In the presence of macroions the excess surface charge layer may extend to 2.0. nm. For the same droplet size, iodide and model hydronium ions show considerably higher concentration than the sodium and chloride ions. <br></div><div>We also find that differences in the average water dipole orientation in the presence of cations and anions in this layer are reflected in the charge distributions. Within the surface charge layer, the number of hydrogen bonds reduces gradually relative to the droplet interior where the number of hydrogen bonds is on the average 2.9 for droplets of diameter < 4 nm and 3.5 for larger droplets. The decrease in the number of hydrogen bonds from the interior to the surface is less pronounced in larger droplets. In droplets with diameter < 4 nm and high concentration of ions the charge of the ions is not compensated only by the solvent polarization charge but by the total charge that also includes the other free charge. This finding shows exceptions to the commonly made assumption that the solvent compensates the charge of the ions in solvents with very high dielectric constant. The study provides molecular insight into the bi-layer droplet structure assumed in the equilibrium partitioning model of C. Enke and assesses critical assumptions of the Iribarne-Thomson model for the ion-evaporation mechanism. <br></div>

scholarly journals Molecular Characterization of the Surface Excess Charge Layer in Droplets

2020 ◽  
Author(s):  
Victor Kwan ◽  
Styliani Consta
Keyword(s):  
Hydrogen Bonds ◽  
Droplet Size ◽  
Ion Concentration ◽  
Excess Charge ◽  
Surface Excess ◽  
Concentration Region ◽  
Charge Layer ◽  
Concentration Of Ions ◽  
Ion Evaporation ◽  
Evaporation Mechanism

<div>Charged droplets play a central role in native mass spectrometry, atmospheric aerosols and in serving as micro-reactors for accelerating chemical reactions. The surface excess charge layer (SECL) in droplets has often been associated with distinct chemistry. Using molecular simulations for droplets with Na+ and Cl- ions we have found that this layer is ≈ 1.5−1.7 nm thick and depending on the droplet size it includes 33%-55% of the total number of ions. Here, we examine the effect of droplet size and nature of ions in the structure of SECL by using molecular dynamics. We find that in the presence of simple ions the thickness of the surface excess charge layer is invariant not only with respect to droplet size but also with respect to the nature of the simple ions and it is not sensitive to fine details of different force fields used in our simulations.</div><div> In the presence of macroions the SECL may extend to 2.0. nm. For the same droplet size, iodide and model H3O+ ions show considerably higher concentration than the sodium and chloride ions. In nano-drops, the SECL does not have the highest concentration of ions. We identify the maximum ion concentration region that may overlap with SECL in nano-drops. We also find that the differences in the average water dipole orientation in the presence of cations and anions in this layer are reflected in the charge distributions. Within the surface charge layer, the number of hydrogen bonds reduces gradually relative to the droplet interior where the number of hydrogen bonds is on the average 2.9 for droplets of diameter < 4 nm and 3.5 for larger droplets. The decrease in the number of hydrogen bonds from the interior to the surface is less pronounced in larger droplets. In droplets with diameter < 4 nm and high concentration of ions the charge of the ions is not compensated only by the solvent polarization charge but by the total charge that also includes the other free charge. This finding shows exceptions to the commonly made assumption that the solvent compensates the charge of the ions in solvents with very high dielectric constant. The study provides molecular insight into the bi-layer droplet structure assumed in the equilibrium partitioning model (EPM) of C. Enke and assesses critical assumptions of the Iribarne-Thomson model for the ion-evaporation mechanism. We suggest the extension of the bi-layer droplet structure in EPM to include the maximum ion concentration region that may not coincide with SECL in nanodrops. We compute the ion concentrations in SECL, which are those that should enter the kinetic equation in the ion-evaporation mechanism, instead of the overall drop ion concentration that has been used thus far.<br></div>

scholarly journals Molecular Characterization of the Surface Excess Charge Layer in Droplets

2020 ◽  
Author(s):  
Victor Kwan ◽  
Styliani Consta
Keyword(s):  
Hydrogen Bonds ◽  
Droplet Size ◽  
Ion Concentration ◽  
Excess Charge ◽  
Surface Excess ◽  
Concentration Region ◽  
Charge Layer ◽  
Concentration Of Ions ◽  
Ion Evaporation ◽  
Evaporation Mechanism

<div>Charged droplets play a central role in native mass spectrometry, atmospheric aerosols and in serving as micro-reactors for accelerating chemical reactions. The surface excess charge layer (SECL) in droplets has often been associated with distinct chemistry. Using molecular simulations for droplets with Na+ and Cl- ions we have found that this layer is ≈ 1.5−1.7 nm thick and depending on the droplet size it includes 33%-55% of the total number of ions. Here, we examine the effect of droplet size and nature of ions in the structure of SECL by using molecular dynamics. We find that in the presence of simple ions the thickness of the surface excess charge layer is invariant not only with respect to droplet size but also with respect to the nature of the simple ions and it is not sensitive to fine details of different force fields used in our simulations.</div><div> In the presence of macroions the SECL may extend to 2.0. nm. For the same droplet size, iodide and model H3O+ ions show considerably higher concentration than the sodium and chloride ions. In nano-drops, the SECL does not have the highest concentration of ions. We identify the maximum ion concentration region that may overlap with SECL in nano-drops. We also find that the differences in the average water dipole orientation in the presence of cations and anions in this layer are reflected in the charge distributions. Within the surface charge layer, the number of hydrogen bonds reduces gradually relative to the droplet interior where the number of hydrogen bonds is on the average 2.9 for droplets of diameter < 4 nm and 3.5 for larger droplets. The decrease in the number of hydrogen bonds from the interior to the surface is less pronounced in larger droplets. In droplets with diameter < 4 nm and high concentration of ions the charge of the ions is not compensated only by the solvent polarization charge but by the total charge that also includes the other free charge. This finding shows exceptions to the commonly made assumption that the solvent compensates the charge of the ions in solvents with very high dielectric constant. The study provides molecular insight into the bi-layer droplet structure assumed in the equilibrium partitioning model (EPM) of C. Enke and assesses critical assumptions of the Iribarne-Thomson model for the ion-evaporation mechanism. We suggest the extension of the bi-layer droplet structure in EPM to include the maximum ion concentration region that may not coincide with SECL in nanodrops. We compute the ion concentrations in SECL, which are those that should enter the kinetic equation in the ion-evaporation mechanism, instead of the overall drop ion concentration that has been used thus far.<br></div>

The Long Term Spatial-temporal Distribution of Aerosol Optical Depth and Its Associated Atmospheric Circulation Over Southeast Africa.

2021 ◽  
Author(s):  
Matthews Nyasulu ◽  
Md. Mozammel Haque ◽  
Bathsheba Musonda ◽  
Cao Fang
Keyword(s):  
Human Health ◽  
Atmospheric Circulation ◽  
Atmospheric Aerosols ◽  
Crop Residues ◽  
Temporal Distribution ◽  
Western Coast ◽  
High Concentration ◽  
Anthropogenic Aerosols ◽  
Anthropogenic Aerosol

Abstract Recent studies have revealed significant impacts of increased concentration of anthropogenic aerosols in the atmosphere to both climate and human health. Southeast Africa is one of the regions where studies related to atmospheric aerosols remain scant, causing high uncertainty in predicting and understanding the impacts of these aerosols to both climate and human health. The present study therefore has investigated the long term spatial-temporal distribution of atmospheric aerosols, trends, its relationship with cloud properties and the associated atmospheric circulation over the region. High concentration of aerosol has been detected during the dry months of September to November (SON) while low during March to May (MAM) and June-July (JJA) seasons in most areas. Highest 550 was recorded in areas with low elevation such as over Lake Malawi, Zambezi valley and along the western coast of the Indian Ocean. The average of the detected concentration is however low as compared to highly polluted regions of the globe. Statistical analyses revealed insignificant change of AOD550 in most areas between 2002 and 2020 time period. The study has also revealed seasonality of aerosol distribution highly influenced by changes in atmospheric circulation. Burning of biomass during dry months such bush fires and burning of crop residues remain the major source of anthropogenic aerosol concentration over Southeast Africa hence needs to be controlled.

scholarly journals Effect of Dissolved Organic Matter on Agglomeration and Removal of CuO Nanoparticles by Coagulation

Processes ◽  
2019 ◽  
Vol 7 (7) ◽  
pp. 455 ◽  
Author(s):  
Rizwan Khan ◽  
Muhammad Ali Inam ◽  
Muhammad Akram ◽  
Ahmed Uddin ◽  
Sarfaraz Khan ◽  
...  
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Industrial Applications ◽  
Water Bodies ◽  
Hydrodynamic Diameter ◽  
Excess Charge ◽  
High Concentration ◽  
Potential Threat ◽  
Cuo Nps ◽  
Coagulation Process

Engineered nanomaterials (ENMs), such as copper oxide nanoparticles (CuO NPs), are emerging as pollutants extensively used in many commercial and industrial applications, thus raising environmental concerns due to their release into water bodies. It is, therefore, essential to remove these pollutants from water bodies in order to minimize the potential threat to the aquatic environment and human health. The objective of this study was to investigate the removal of CuO NPs from waters by the coagulation process. This study also explored the efficiency of coagulation to remove hydrophobic/hydrophilic dissolved organic matter (DOM) and turbidity with varying polyaluminum chloride (PACl) doses. According to the results, a high concentration of DOM affects both the CuO NPs zeta potential and hydrodynamic diameter, thereby decreasing the agglomeration behavior. At effective coagulation zone (ECR), high removal of CuO NPs (>95%) was observed for all studied waters (hydrophobic and hydrophilic waters), above ECR excess charge induced by coagulant restabilized particles in solution. Furthermore, waters containing hydrophobic DOM and those with high UV254nm values needed more coagulant dose than hydrophilic waters to obtain similar CuO NP removals. The primary mechanism involved in CuO NPs removal might be charge neutralization. These findings suggest that PACl is an effective coagulant in the removal of CuO NPs; however, water characteristics are an influencing factor on the removal performance of ENMs during the coagulation process.

scholarly journals TwoN-(2-phenylethyl)nitroaniline derivatives as precursors for slow and sustained nitric oxide release agents

2016 ◽  
Vol 72 (5) ◽  
pp. 405-410 ◽  
Author(s):  
Alec R. Badour ◽  
John A. Wisniewski ◽  
Dillip K. Mohanty ◽  
Philip J. Squattrito
Keyword(s):  
Nitric Oxide ◽  
Hydrogen Bond ◽  
Hydrogen Bonds ◽  
Molecular Conformation ◽  
Therapeutic Interventions ◽  
Secondary Amines ◽  
Asymmetric Unit ◽  
High Concentration ◽  
Nitric Oxide Release ◽  
Π Interactions

Notwithstanding its simple structure, the chemistry of nitric oxide (NO) is complex. As a radical, NO is highly reactive. NO also has profound effects on the cardiovascular system. In order to regulate NO levels, direct therapeutic interventions include the development of numerous NO donors. Most of these donors release NO in a single high-concentration burst, which is deleterious.N-Nitrosated secondary amines release NO in a slow, sustained, and rate-tunable manner. Two new precursors to sustained NO-releasing materials have been characterized.N-[2-(3,4-Dimethoxyphenyl)ethyl]-2,4-dinitroaniline, C16H17N3O6, (I), crystallizes with one independent molecule in the asymmetric unit. The adjacent amine and nitro groups form an intramolecular N—H...O hydrogen bond. Theanticonformation about the phenylethyl-to-aniline C—N bond leads to the planes of the arene and aniline rings being approximately perpendicular. Molecules are linked into dimers by weak intermolecular N—H...O hydrogen bonds such that each amine H atom participates in a three-center interaction with two nitro O atoms. The dimers pack so that the arene rings of adjacent molecules are not parallel and π–π interactions do not appear to be favored.N-(4-Methylsulfonyl-2-nitrophenyl)-L-phenylalanine, C16H16N2O6S, (II), with an optically active center, also crystallizes with one unique molecule in the asymmetric unit. The L enantiomer was establishedviathe configuration of the starting material and was confirmed by refinement of the Flack parameter. As in (I), there is an intramolecular N—H...O hydrogen bond between adjacent amine and nitro groups. The conformation of the molecule is such that the arene rings display a dihedral angle ofca60°. Unlike (I), molecules are not linkedviaintermolecular N—H...O hydrogen bonds. Rather, the carboxylic acid H atom forms a classic, approximately linear, O—H...O hydrogen bond with a sulfone O atom. Pairs of molecules related by twofold rotation axes are linked into dimers by two such interactions. The packing pattern features a zigzag arrangement of the arene rings without apparent π–π interactions. These structures are compared with reported analogues, revealing significant differences in molecular conformation, intermolecular interactions, and packing that result from modest changes in functional groups. The structures are discussed in terms of potential NO-release capability.

N—H...X (X = Cl and Br) hydrogen bonds in three isomorphous 3,5-dichloropyridinium salts

2017 ◽  
Vol 73 (10) ◽  
pp. 803-809 ◽  
Author(s):  
Ai Wang ◽  
Ulli Englert
Keyword(s):  
Hydrogen Bonds ◽  
Small Molecules ◽  
Crystal Engineering ◽  
Electrostatic Interactions ◽  
Halogen Bond ◽  
Halogen Bonds ◽  
Dipole Orientation ◽  
Halide Ligand ◽  
Van Der Waals Radii ◽  
Short Contacts

Specific short contacts are important in crystal engineering. Hydrogen bonds have been particularly successful and together with halogen bonds can be useful for assembling small molecules or ions into crystals. The ionic constituents in the isomorphous 3,5-dichloropyridinium (3,5-diClPy) tetrahalometallates 3,5-dichloropyridinium tetrachloridozincate(II), (C5H4Cl2N)2[ZnCl4] or (3,5-diClPy)2ZnCl4, 3,5-dichloropyridinium tetrabromidozincate(II), (C5H4Cl2N)2[ZnBr4] or (3,5-diClPy)2ZnBr4, and 3,5-dichloropyridinium tetrabromidocobaltate(II), (C5H4Cl2N)2[CoBr4] or (3,5-diClPy)2CoBr4, arrange according to favourable electrostatic interactions. Cations are preferably surrounded by anions and vice versa; rare cation–cation contacts are associated with an antiparallel dipole orientation. N—H...X (X = Cl and Br) hydrogen bonds and X...X halogen bonds compete as closest contacts between neighbouring residues. The former dominate in the title compounds; the four symmetrically independent pyridinium N—H groups in each compound act as donors in charge-assisted hydrogen bonds, with halogen ligands and the tetrahedral metallate anions as acceptors. The M—X coordinative bonds in the latter are significantly longer if the halide ligand is engaged in a classical X...H—N hydrogen bond. In all three solids, triangular halogen-bond interactions are observed. They might contribute to the stabilization of the structures, but even the shortest interhalogen contacts are only slightly shorter than the sum of the van der Waals radii.

Subsurface Space-Charge Dopant Segregation to Compensate Surface Excess Charge in a Perovskite Oxide

2016 ◽  
Vol 55 (33) ◽  
pp. 9680-9684 ◽  
Author(s):  
Sung-Yoon Chung ◽  
Si-Young Choi ◽  
Hye-In Yoon ◽  
Hye-Sung Kim ◽  
Hyung Bin Bae
Keyword(s):  
Space Charge ◽  
Perovskite Oxide ◽  
Excess Charge ◽  
Surface Excess ◽  
Dopant Segregation

scholarly journals Simulation of Effects of Atmospheric Aerosols on Deep Turbulent Convective Clouds Using a Spectral Microphysics Mixed-Phase Cumulus Cloud Model. Part II: Sensitivity Study

2004 ◽  
Vol 61 (24) ◽  
pp. 2983-3001 ◽  
Author(s):  
A. Khain ◽  
A. Pokrovsky
Keyword(s):  
Atmospheric Aerosols ◽  
Cloud Model ◽  
Precipitation Amount ◽  
Sensitivity Study ◽  
Total Precipitation ◽  
High Concentration ◽  
Close Coupling ◽  
Convective Clouds ◽  
Warm Rain ◽  
Bulk Parameterization

Abstract Effects of different size distributions of cloud condensational nuclei (CCN) on the evolution of deep convective clouds under dry unstable continental thermodynamic conditions are investigated using the spectral microphysics Hebrew University Cloud Model (HUCM). In particular, high supercooled water content just below the level of homogeneous freezing, as well as an extremely high concentration of ice crystals above the level, observed recently by Rosenfeld and Woodley at the tops of growing clouds in Texas, were successfully reproduced. Numerical experiments indicate a significant decrease in accumulated precipitation in smoky air. The fraction of warm rain in the total precipitation amount increases with a decrease in the CCN concentration. The fraction is low in smoky continental air and is dominating in clean maritime air. As warm rain is a smaller fraction of total precipitation, the decrease in the accumulated rain amount in smoky air results mainly from the reduction of melted precipitation. It is shown that aerosols significantly influence cloud dynamics leading to the elevation of the level of precipitating particle formation. The falling down of these particles through dry air leads to a loss in precipitation. Thus, close coupling of microphysical and dynamical aerosol effects leads to the rain suppression from clouds arising in dry smoky air. The roles of freezing, CCN penetration through lateral cloud boundaries, and turbulent effects on cloud particles collisions are evaluated. Results, obtained using spectral microphysics, were compared with those obtained using two well-known schemes of bulk parameterization. The results indicate that the bulk parameterization schemes do not reproduce well the observed cloud microstructure.

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