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Stability and Growth of Composite Atmospheric Nanoclusters Studied by Molecular Dynamics Simulations
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2014. , viii, 70 p.
Series
TRITA-BIO-Report, ISSN 1654-2312 ; 2014:09
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:kth:diva-145248ISBN: 978-91-7595-173-7 (print)OAI: oai:DiVA.org:kth-145248DiVA: diva2:717336
Public defence
2014-06-05, FB54, AlbaNova University Center, Roslagsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20140520

Available from: 2014-05-20 Created: 2014-05-14 Last updated: 2014-05-20Bibliographically approved
List of papers
1. Molecular Dynamics Simulations of the Surface Tension and Structure of Salt Solutions and Clusters
Open this publication in new window or tab >>Molecular Dynamics Simulations of the Surface Tension and Structure of Salt Solutions and Clusters
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2012 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 116, no 10, 3198-3204 p.Article in journal (Refereed) Published
Abstract [en]

Sodium halides, which are abundant in sea salt aerosols, affect the optical properties of aerosols and are active in heterogeneous reactions that cause ozone depletion and acid rain problems. Interfacial properties, including surface tension and halide anion distributions, are crucial issues in the study of the aerosols. We present results from molecular dynamics simulations of water solutions and clusters containing sodium halides with the interatomic interactions described by a conventional force field. The simulations reproduce experimental observations that sodium halides increase the surface tension with respect to pure water and that iodide anions reach the outermost layer of water clusters or solutions. It is found that the van der Waals interactions have an impact on the distribution of the halide anions and that a conventional force field with optimized parameters can model the surface tension of the salt solutions with reasonable accuracy.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-93933 (URN)10.1021/jp209178s (DOI)000301509500017 ()2-s2.0-84863342270 (Scopus ID)
Funder
Swedish Research Council, 2009-3614Swedish e‐Science Research Center
Note

QC 20120504

Available from: 2012-05-04 Created: 2012-05-03 Last updated: 2014-05-20Bibliographically approved
2. Combined Effect of Glycine and Sea Salt on Aerosol Cloud Droplet Activation Predicted by Molecular Dynamics Simulations
Open this publication in new window or tab >>Combined Effect of Glycine and Sea Salt on Aerosol Cloud Droplet Activation Predicted by Molecular Dynamics Simulations
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2013 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 117, no 41, 10746-10752 p.Article in journal (Refereed) Published
Abstract [en]

The present study illustrates the combined effect of organic and inorganic compounds on cloud droplet nucleation and activation processes representative for the marine environment. Amino acids and sea salt are common marine cloud condensation nuclei (CCN) which act as a prerequisite for growth of cloud droplets. The chemical and physical properties of these CCN play a key role for interfacial properties such as surface tension, which is important for the optical properties of clouds and for heterogeneous reactions. However, there is a lack of detailed information and in situ measurements of surface tension of such nanosized droplets. Here we present a study of the combined effect of zwitterionic glycine (ZGLY) and sea salt in nanosized water droplets using molecular dynamics simulations, where particular emphasis is placed on the surface tension for the nanosized droplets. The critical supersaturation is estimated by the Kohler equation. It is found that dissolved sea salt interacts with ZGLY through a water bridge and weakens the hydrogen bonds among ZGLYs, which has a significant effect on both surface tension and water vapor supersaturation. Clusters of glycine mixed with sea salt deliquesce more efficiently and have higher growth factors.

Keyword
Linear Constraint Solver, Particle Mesh Ewald, Surface-Tension, Dimethyl Sulfide, Amino-Acids, Clusters, Sulfur, Albedo, Water, Gromacs
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-134568 (URN)10.1021/jp407538x (DOI)000326126100020 ()2-s2.0-84886874900 (Scopus ID)
Note

QC 20131127

Available from: 2013-11-27 Created: 2013-11-25 Last updated: 2014-05-20Bibliographically approved
3. Origin of Ion Selectivity at the Air/Water Interface
Open this publication in new window or tab >>Origin of Ion Selectivity at the Air/Water Interface
2015 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 6, 4311-4318 p.Article in journal (Refereed) Published
Abstract [en]

Among many characteristics of ions, their capability to accumulate at air/water interfaces is a particular issue that has been the subject of much research attention. For example, the accumulation of halide anions (Cl-, Br-, I-) at the water surface is of great importance to heterogeneous reactions that are of environmental concern. However, the actual mechanism that drives anions towards the air/water interface remains unclear. In this work, we have performed atomistic simulations using polarizable models to mimic ionic behavior under atmospheric conditions. We find that larger anions are abundant at the water surface and that the cations are pulled closer to the surface by the counterions. We propose that polarization effects stabilize the anions with large radii when approaching the surface. This energetically more favorable situation is caused by the fact that the more polarized anions at the surface attract water molecules more strongly. Of relevance is also the ordering of the surface water molecules with their hydrogen atoms pointing outwards which induce an external electronic field that leads to a different surface behavior of anions and cations. The water-water interaction is weakened by the distinct water-ion attraction, a point contradicting the proposition that F- is a kosmotrope. The simulation results thus allow us to obtain a more holistic understanding of the interfacial properties of ionic solutions and atmospheric aerosols.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-145428 (URN)10.1039/C4CP03338H (DOI)000349005900040 ()
Note

QC 20150310. Updated from manuscript to article in journal.

Available from: 2014-05-20 Created: 2014-05-20 Last updated: 2015-03-10Bibliographically approved
4. Cross-Linked Polysaccharide Assemblies in Marine Gels: An Atomistic Simulation
Open this publication in new window or tab >>Cross-Linked Polysaccharide Assemblies in Marine Gels: An Atomistic Simulation
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2013 (English)In: Journal of Physical Chemistry Letters, ISSN 1948-7185, Vol. 4, no 16, 2637-2642 p.Article in journal (Refereed) Published
Abstract [en]

Marine polymeric gels or colloidal nano- and microgels have been shown to contribute significantly to the primary marine aerosol and cloud condensation nuclei over remote marine areas. A microscopic understanding of such biologically derived matter at the sea air interface is important for future development of global climate models, but unfortunately cannot be obtained from modern characterization techniques. In this contribution, we employ molecular dynamics simulations to reveal the atomistic details of marine polymeric gels represented by anionic polysaccharide assemblies. The ionic bonds formed between polysaccharides and metal ions in seawater as well as the hydrophobic contribution to surface area are investigated in detail, and destabilization of the assemblies upon removal of Ca2+ or acidification is explained. These results provide insight into physicochemical properties of polysaccharide-Ca2+ structures and enable future studies of their roles of in the wetting process of cloud droplet activation.

Keyword
Central Arctic-Ocean, Surface Microlayer, Force-Field, Particles, Aerosol, Summer, Water, Microgels, Dynamics, Matter
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-128473 (URN)10.1021/jz401276r (DOI)000323300900007 ()2-s2.0-84882367051 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20130912

Available from: 2013-09-12 Created: 2013-09-12 Last updated: 2014-05-20Bibliographically approved
5. Molecular Dynamics Simulations Reveal the Assembly Mechanism of Polysaccharides in Marine Aerosols
Open this publication in new window or tab >>Molecular Dynamics Simulations Reveal the Assembly Mechanism of Polysaccharides in Marine Aerosols
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2014 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 47, 25935-25941 p.Article in journal (Other academic) Published
Abstract [en]

The high Arctic marine environment has recently detected polymer gels in atmospheric aerosol particles and cloud water originating from the surface microlayer of the open leads within the pack ice area. These polysaccharide molecules are water insoluble but water solvated, highly surface-active and highly hydrated (99% water). In order to add to the understanding and to complement missing laboratory characterization of marine polymer gels we have in this work performed an atomistic study of the assembly process and interfacial properties of polysaccharides. Our study reveals a number of salient features of the microscopic process behind polysaccharide assembly into nanogels. With three- and four-repeating units the polysaccharides assemble into a cluster in 50 ns. The aggregates grow quicker by absorbing one or two polymers each time, depending on the unit length and the type of inter-bridging cation. Although both the hydrophobic and hydrophilic domains are contracted, the latter dominates distinctly upon the contraction of solvent accessible surface areas. The establishment of inter-chain hydrogen-bonds is the key to the assembly while ionic bridges can further promote aggregation. During the assembly of the more bent four-unit polymers, intra-chain hydrogen bonds are significantly diminished by Ca2+. Meanwhile, the percentage of Ca2+ acting as an ionic bridge is more eminent, highlighting the significance of Ca2+ ions for longer-chain polysaccharides. The aggregates are able to enhance surface tension more in the presence of Ca2+ than in the presence of Na+ owing to their more compact structure. These conclusions all demonstrate that studies of the present kind provide insight into the self-assembly process and interfacial properties of marine gels. We hope this understanding will keep up the interest in the complex and the fascinating relationship between marine microbiology, atmospheric aerosols, clouds and climate.

National Category
Natural Sciences
Identifiers
urn:nbn:se:kth:diva-145247 (URN)10.1039/c4cp03423f (DOI)000345208200031 ()2-s2.0-84912029071 (Scopus ID)
Note

QC 20150113. Updated from manuscript to article in journal.

Available from: 2014-05-14 Created: 2014-05-14 Last updated: 2015-01-13Bibliographically approved

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