Exploring the nature of the interactions between the molecules of the sodium dodecyl sulfate and water in crystal phases and in the water/ vacuum interface
Por:
Aray, Yosslen, Parra, Jose G., PAREDES, RICARDO, Alvarez, Luis Javier, Diaz-Barrios, Antonio
Publicada:
1 jun 2020
Categoría:
Multidisciplinary
Resumen:
The nature of the interaction between the molecules of the sodium
dodecyl sulfate surfactant forming two crystal phases, one anhydrous,
NaC12H25O4S and the other, NaC12H25O4S center dot H2O, hydrated with one
water molecule for unit cell, has been studied in detail using the
quantum theory of atoms in molecules and a localized electron detector
function. It was found that for the anhydrous crystal, the head groups
of the surfactant molecules are linked into a head-to-head pattern, by a
bond path network of Na-O ionic bonds, where each Na+ atom is attached
to four SO4- groups. For the hydrated crystal, in addition to these four
bonds for Na+, two additional ones appear with the oxygen atoms of the
water molecules, forming a bond paths network of ionic Na-O bonds, that
link the Na+ atoms with the SO4- groups and the H2O molecules. Each H2O
molecule is bonded to two SO4- groups via hydrogen bonds, while the SO4-
groups are linked to a maximum of four Na+ atoms. The phenomenon of ag-
gregation of the sodium dodecyl sulfate molecules at the liquid
water/vacuum interface was studied using NVT molecular dynamics
simulations. We have found that for surfactant aggregates, the Na+ ions
are linked to a maximum of three SO4- groups and three water molecules
that form Na-O bonds. Unlike hydrated crystal, each of the O atoms that
make these Na-O bonds is linked to only one Na+ ion. Despite these
differences, like the crystal phases, the surfactant molecules tend to
form a head-to-head network pattern of ionic Na-O bonds that link their
heads. The present results indicate that the clustering of anionic
surfactant at the water/vacuum interface is a consequence of the
electrostatic alignment of the cationic and anionic groups as occurs in
the crystalline phases of sodium dodecyl sulfate.
Filiaciones:
Aray, Yosslen:
Univ Ciencias Aplicadas & Ambientales, Fac Ciencias, Campus Univ Norte,Calle 222 55-37, Bogota, Colombia
Parra, Jose G.:
Univ Carabobo, Fac Expt Ciencias & Tecnol, FACYT, Dept Quim,Lab Quim Computac, Barbula, Venezuela
PAREDES, RICARDO:
Univ Iberoamer, Dept Fis & Matem, Prolongac Paseo Reforma 880, Mexico City 01219, DF, Mexico
Alvarez, Luis Javier:
Univ Nacl Autonoma Mexico, Inst Matemat, Unidad Cuernavaca, Lab Simulac, AP 273-3 Admon 3, Cuernavaca 62251, Morelos, Mexico
Diaz-Barrios, Antonio:
Escuela Ciencias Quim & Ingn, Yachay Tech, Urcuqui, Ecuador
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