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Molecular modeling of surfactant-cov...

University of Florida.

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Molecular modeling of surfactant-covered oil-water interfaces .

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Molecular modeling of surfactant-covered oil-water interfaces ./
作者:	Gupta, Ashish.
面頁冊數:	96 p.
附註:	Advisers: Dmitry I. Kopelevich; Anuj Chauhan.
Contained By:	Dissertation Abstracts International69-10B.
標題:	Engineering, Chemical. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3334464
ISBN:	9780549873709

Molecular modeling of surfactant-covered oil-water interfaces .
Gupta, Ashish.

Molecular modeling of surfactant-covered oil-water interfaces . - 96 p.

Advisers: Dmitry I. Kopelevich; Anuj Chauhan.

Thesis (Ph.D.)--University of Florida, 2008.

Mass transport across oil-water interface and surfactant-covered oil-water interfaces plays an important role in numerous applications. In the current work, we use coarse-grained molecular dynamics simulations to investigate model surfactant-free oil-water interface and oil-water interfaces covered by monolayers of non-ionic surfactants of various length. Several properties of the surfactant monolayers relevant to the mass transport are considered, including the monolayer microstructure, dynamics and a free energy barrier to the solute transport. It is observed that the dominant contribution of a surfactant monolayer to the free energy barrier is a steric repulsion caused by a local density increase inside the monolayer. The local densities, and hence the free energy barriers, are larger for monolayers composed of longer surfactants. Since it is likely that the solute transport mechanism involves a sequence of jumps between short-lived pores within a monolayer, we perform a detailed analysis of structure, size, and life-time of these pores. We demonstrate that the pore statistics is consistent with predictions of the percolation theory and apply this theory to identify characteristic length-scale of the monolayer microstructure. The obtained pore structures are sensitive to minute changes of surfactant configurations occurring on the picosecond time-scale. To reduce this sensitivity, the pores are averaged over short time intervals. The optimal duration of these time intervals is estimated from analysis of dynamics of pores with diameters comparable to or exceeding the characteristic percolation length-scale. The developed approach allows one to filter out transient events of the pore dynamics and to focus on events leading to substantial changes of the monolayer microstructure.

ISBN: 9780549873709Subjects--Topical Terms:

1018531
Engineering, Chemical.

Molecular modeling of surfactant-covered oil-water interfaces .
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245 1 0 $a Molecular modeling of surfactant-covered oil-water interfaces .
300 $a 96 p.
500 $a Advisers: Dmitry I. Kopelevich; Anuj Chauhan.
500 $a Source: Dissertation Abstracts International, Volume: 69-10, Section: B, page: 6268.
502 $a Thesis (Ph.D.)--University of Florida, 2008.
520 $a Mass transport across oil-water interface and surfactant-covered oil-water interfaces plays an important role in numerous applications. In the current work, we use coarse-grained molecular dynamics simulations to investigate model surfactant-free oil-water interface and oil-water interfaces covered by monolayers of non-ionic surfactants of various length. Several properties of the surfactant monolayers relevant to the mass transport are considered, including the monolayer microstructure, dynamics and a free energy barrier to the solute transport. It is observed that the dominant contribution of a surfactant monolayer to the free energy barrier is a steric repulsion caused by a local density increase inside the monolayer. The local densities, and hence the free energy barriers, are larger for monolayers composed of longer surfactants. Since it is likely that the solute transport mechanism involves a sequence of jumps between short-lived pores within a monolayer, we perform a detailed analysis of structure, size, and life-time of these pores. We demonstrate that the pore statistics is consistent with predictions of the percolation theory and apply this theory to identify characteristic length-scale of the monolayer microstructure. The obtained pore structures are sensitive to minute changes of surfactant configurations occurring on the picosecond time-scale. To reduce this sensitivity, the pores are averaged over short time intervals. The optimal duration of these time intervals is estimated from analysis of dynamics of pores with diameters comparable to or exceeding the characteristic percolation length-scale. The developed approach allows one to filter out transient events of the pore dynamics and to focus on events leading to substantial changes of the monolayer microstructure.
520 $a To obtain the solute transport rate, we develop a Langevin equation for the solute transport. It is frequently assumed that the fluctuations of the thermal random force are adequately described by the white noise, i.e. that the correlation time of the random force is much smaller than the characteristic time of the solute transport. We demonstrate that although this assumption is correct when the solute is located sufficiently far from the interface, the correlation time of the random force becomes significant within a very narrow (less than 1 nm wide) region of the interface. We demonstrate that the slow fluctuations of the random force in this narrow region are caused by fluctuations of the interface. Unlike the random collisions of the solute with the solvent molecules in homogeneous fluids, the interface fluctuations change the composition of the solvation shell of the solute. We propose a multi-dimensional Langevin equation which explicitly accounts for the solute interface coupling and validate it for surfactant-free and surfactant-covered interfaces. The strength of the solute-interface coupling is determined by the magnitude of the protrusions of the interface formed when solute is constrained in the vicinity of the interface. Similar phenomena is expected to occur in other interfacial systems such as lipid bilayers.
590 $a School code: 0070.
650 4 $a Engineering, Chemical. $3 1018531
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710 2 $a University of Florida. $3 718949
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