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Molecular dynamics studies of organi...

University of Maryland, College Park., Applied Mathematics and Scientific Computation.

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Molecular dynamics studies of organic-coated nano aerosols.

紀錄類型:	書目-語言資料,印刷品 : Monograph/item
正題名/作者:	Molecular dynamics studies of organic-coated nano aerosols./
作者:	Chakraborty, Purnendu.
面頁冊數:	128 p.
附註:	Adviser: Michael R. Zachariah.
Contained By:	Dissertation Abstracts International69-05B.
標題:	Atmospheric Sciences. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3307833
ISBN:	9780549572596

Molecular dynamics studies of organic-coated nano aerosols.
Chakraborty, Purnendu.

Molecular dynamics studies of organic-coated nano aerosols. - 128 p.

Adviser: Michael R. Zachariah.

Thesis (Ph.D.)--University of Maryland, College Park, 2008.

Atmospheric aerosols play an important role in atmospheric processes. These aerosol particles can affect climate through scattering, transmission and absorption of radiation as well as acting as cloud condensation nuclei. It has recently been found that fatty acids reside on the surfaces of marine and continental aerosols. In this research, an attempt has been made to understand the structures and properties of such organic coated aerosols using Molecular Dynamics simulation. The model particle consisted of a water droplet coated with fatty acid. The density profile (using both Coarse-Grained and Atomistic/United atom models) demonstrated that such aerosol particles have an inverted micelle structure consisting of an aqueous core and with the hydrophobic hydrocarbon tails exposed to the atmosphere. For smaller chains, with the organic molecules directed radially outwards from the water---organic interface) the normal pressure profile showed that the organic coating is under tension resulting in a 'negative' surface tension. As a result, such particles would have an inverse Kelvin vapor pressure effect and would be able to process water vapor despite the hydrophobic surface.

ISBN: 9780549572596Subjects--Topical Terms:

1019179
Atmospheric Sciences.

Molecular dynamics studies of organic-coated nano aerosols.
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245 1 0 $a Molecular dynamics studies of organic-coated nano aerosols.
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500 $a Adviser: Michael R. Zachariah.
500 $a Source: Dissertation Abstracts International, Volume: 69-05, Section: B, page: 3201.
502 $a Thesis (Ph.D.)--University of Maryland, College Park, 2008.
520 $a Atmospheric aerosols play an important role in atmospheric processes. These aerosol particles can affect climate through scattering, transmission and absorption of radiation as well as acting as cloud condensation nuclei. It has recently been found that fatty acids reside on the surfaces of marine and continental aerosols. In this research, an attempt has been made to understand the structures and properties of such organic coated aerosols using Molecular Dynamics simulation. The model particle consisted of a water droplet coated with fatty acid. The density profile (using both Coarse-Grained and Atomistic/United atom models) demonstrated that such aerosol particles have an inverted micelle structure consisting of an aqueous core and with the hydrophobic hydrocarbon tails exposed to the atmosphere. For smaller chains, with the organic molecules directed radially outwards from the water---organic interface) the normal pressure profile showed that the organic coating is under tension resulting in a 'negative' surface tension. As a result, such particles would have an inverse Kelvin vapor pressure effect and would be able to process water vapor despite the hydrophobic surface.
520 $a Following the work on surface tension, the rate of water uptake by coated aerosols was computed. It was found that the sticking coefficient of water vapor on such particles was about a sixth of that on pure water droplets. This may seem to imply that the net condensation rate is lower, but we also need to take into account the evaporation of water from such particles. With a significant reduction in the evaporation rate (the coating lends greater stability to the particle resulting in reduced evaporation rate), the equilibrium vapor pressure of water on such particles reduced, resulting in a "net water attractor". Thus if such structures were created in sufficient concentration, they might be important contributors in the cloud condensation process. Next the effect of longer Fatty acid molecules and branched surfactants on the structure and properties of coated particles was studied. It was found that in either case, due to stronger organic---organic interactions, the surfactant molecules tend to align themselves parallel to each other forcing local flattening of the underlying water substrate and consequently such particles behaved in a manner consistent with an "oily" drop, in sharp contrast to the case of shorter chains, where the particle was a "net water attractor".
520 $a Finally, the effect of organic coating on the Stokes drag of functionalized nanoparticles was studied. This work was motivated by a recent experimental study in which the thickness of Self Assembled Monolayers on Gold nanoparticles was characterized using a measurement process that relies on the determination of the size of a charged particle through knowledge of the drag force. The thickness of the coating was found to ~35% less than that predicted by a rigid core-shell model. This suggests that the functionalized Au-NP would have an inverted micelle structure. The MD simulations showed that the drag on the coated particle was indeed less than that on the corresponding pure particle, consistent with the experimental observation.
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710 2 $a University of Maryland, College Park. $b Applied Mathematics and Scientific Computation. $3 1021743
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