TY - JOUR

T1 - The electric properties of AOT reverse micelles by molecular dynamics simulations

AU - Kopanichuk, Ilia

AU - Novikov, Valentin A.

AU - Vanin, Aleksandr A.

AU - Brodskaya, Elena N.

PY - 2019/12/15

Y1 - 2019/12/15

N2 - Reverse micelles (RMs) are the main component of a reverse microemulsion. The ionic RMs of sodium and calcium bis(2-ethylhexyl)sulfosuccinate (AOTNa and AOT(2)Ca, respectively), and water clusters of different size in isooctane were simulated by the united-atom molecular dynamics method. The radial density profiles characterized the local structure. The local electric potential and the electric field were calculated to describe the electric layer (EL). The behavior of these functions differs principally from the related quantities in the classical electric double layer. The decrease in the size of RMs leads to a noticeable compression of the EL. The value of the local electric field near the surface of the RM increases significantly with the replacement of Na+ counterions by Ca2+. The mutual compensation of the contributions from water and ions calculated separately was revealed, which results in poor sensitivity of the electric properties of the RMs to salt addition. The mean-square dipole moment was calculated for all considered aggregates. It was shown that this quantity strongly depends on the aggregate size as could be expected due to its fluctuation nature. Comparison of the mean-square dipole moment value obtained by the atomistic simulation with the one obtained within the primitive model witnesses that the strong overestimation of the dielectric permittivity of confined water in the primitive model of the RM leads to a significant decrease in the value of the micellar mean-square dipole moment. (C) 2019 Elsevier B.V. All rights reserved.

AB - Reverse micelles (RMs) are the main component of a reverse microemulsion. The ionic RMs of sodium and calcium bis(2-ethylhexyl)sulfosuccinate (AOTNa and AOT(2)Ca, respectively), and water clusters of different size in isooctane were simulated by the united-atom molecular dynamics method. The radial density profiles characterized the local structure. The local electric potential and the electric field were calculated to describe the electric layer (EL). The behavior of these functions differs principally from the related quantities in the classical electric double layer. The decrease in the size of RMs leads to a noticeable compression of the EL. The value of the local electric field near the surface of the RM increases significantly with the replacement of Na+ counterions by Ca2+. The mutual compensation of the contributions from water and ions calculated separately was revealed, which results in poor sensitivity of the electric properties of the RMs to salt addition. The mean-square dipole moment was calculated for all considered aggregates. It was shown that this quantity strongly depends on the aggregate size as could be expected due to its fluctuation nature. Comparison of the mean-square dipole moment value obtained by the atomistic simulation with the one obtained within the primitive model witnesses that the strong overestimation of the dielectric permittivity of confined water in the primitive model of the RM leads to a significant decrease in the value of the micellar mean-square dipole moment. (C) 2019 Elsevier B.V. All rights reserved.

KW - COMPUTER-SIMULATION

KW - DIELECTRIC-CONSTANTS

KW - SIZE PARAMETERS

KW - DIPOLE-MOMENT

KW - WATER

KW - MICROEMULSIONS

KW - FIELD

KW - FLUCTUATION

KW - SOLVATION

KW - STABILITY

U2 - 10.1016/j.molliq.2019.111960

DO - 10.1016/j.molliq.2019.111960

M3 - статья

VL - 296

JO - Journal of Molecular Liquids

JF - Journal of Molecular Liquids

SN - 0167-7322

M1 - 111960

ER -