Quantum-Chemical Calculations of the Charge Distribution in Ionic Surfactants

Huibers, Paul D. T.

doi:10.1021/la990367l

Cited by 108 publications

(102 citation statements)

References 18 publications

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“…This result agrees with semiempirical computations of single anionic surfactants, and supports the view that the interior of self assembled structures made of SDS surfactants, e.g. micelles, may be polar 58 . An interesting consequence of these polarization effects would be and increase in the penetration of water and ions in the hydrophobic region of the NBF.…”

Section: Conclusion and Final Remarkssupporting

confidence: 88%

“…The possibility of charge transfer effects in these surfactants has been discussed before. Using first-principles computations it has been shown that anionic hydrocarbons such as SDS feature significant charge transfer, which extends from the head group to the terminal methyl group 57,58 . Semiempirical methods indicate that such charge transfer also occurs in normal alkanes, although in the case of dodecane, which is relevant to our system, the charge transfer results in charge separation in the two terminal methyl and methylene groups.…”

Section: Resultsmentioning

confidence: 99%

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Electronic structure computations of Newton Black Films

Bresme

Artacho

2010

J. Mater. Chem.

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We investigate using quantum density functional theory (DFT) the electronic structure of sodium dodecyl sulfate Newton Black Films (NBF), consisting of water sandwiched between surfactants surrounded by vacuum. We generate a classical trajectory of the film using full-atom empirical potentials. DFT theory is employed to investigate the electron density and electrostatic properties of the film. The electrostatic potential derived directly from the electron and nuclear densities shows an important drop towards the vacuum side, similar to recent findings for the water-vacuum interface. We discuss the physical significance of this potential drop. We also consider as an alternative definition of the electrostatic potential, the deformation charge potential (DCP), to quantify the electrostatic properties of the interfaces. The analysis of the DCP potential indicates there is charge separation at the surfactant alkyl tails, showing that the surfactant-vacuum surface has an excess of positive charge. This result is consistent with molecular dynamics simulations employing classical force-fields, which incorporate partial charges to model the surfactant alkyl chain. The DCP potential also gives evidence for the existence of electronic polarization in the hydrophobic region of the NBF, whose origin is connected to charge transfer between the surfactant tails and the head group. We suggest that the deformation charge potential provides a route to compare the electrostatic potentials obtained from DFT and emprirical computations. This idea is illustrated by computing the electrostatic potential of the water-vapor interface. We discuss the relevance of these results in the context of DFT computations of soft interfaces.

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Section: Conclusion and Final Remarkssupporting

confidence: 88%

Section: Resultsmentioning

confidence: 99%

Electronic structure computations of Newton Black Films

Bresme

Artacho

2010

J. Mater. Chem.

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“…One is that the calculation is very complicate. For example, to the binary anionic/cationic system, A = CH 3 (CH 2 ) 11 The other difficulty is the determination of the position for each atom of the surfactants in space. It has been known that there are kinds of movements in a molecule such as the extension, compression, winding and rotation of all kinds bonds, the collision among atoms, and so on, and that those movements make the position of atoms can not be precisely determined and consequently the distance r ij in Lennard-Jones formula cannot be determined.…”

Section: Simplification Of the Calculation Of εmentioning

confidence: 99%

Calculation of the molecular exchanging energy of binary surfactants system on the surface monolayer of aqueous solution

Wang

2007

SCI CHINA SER B

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By using the binary anionic/cationic surfactants system CH 3 (CH 2 ) n OSO − 3 /CH 3 (CH 2 ) n N + (CH 3 ) 3 as an example, the molecular exchanging energy (ε) of adsorption on the surface monolayer of aqueous solution has been studied. ε can be obtained with two methods. One is from the relationship between ε and the molecule interaction parameter (β). This relationship is founded by considering that the adsorption of mixed surfactants on the surface monolayer of solution satisfies the dimensional crystal model condition under which β can be obtained by testing the surface tension of solution. The other is directly from the molecular structure of surfactants with the Lennard-Jones formula. The results for the studied system show that these two methods coincide well. surfactant, molecule exchanging energy, dimensional crystal modelBecause of the existence of molecular interaction, mixed surfactants are often superior to a single one to reduce the surface energy of solution. This phenomenon is called synergism of mixed surfactants [1] . Synergism is very useful in many fields such as mining engineering, oil extraction, pharmaceutical production, cosmetic industry, and so on. However, since there are many kinds of interactions in solution such as the van der Waals force, the Coulomb force and hydrogen bond among surfactants and solvent molecules, the study of the molecular interaction in mixed surfactants solution is very difficult. To our knowledge, only the investigations by Rubingh [2,3] , Rosen [4,5] and their co-workers have been reported so far. In their work, they used a nonideal parameter β, which is also called molecular interaction parameter and was deduced from the regular solution theory, to describe the synergism of mixed surfactants.i.e., The bigger of the absolute value of β when β < 0, the stronger the synergism. β can be determined with the surface tension vs. the logarithm of mixed surfactants concentration curves γ ~lgc, but how to explain the essences of β and synergism quantitatively from the molecular structure, it remains to be further investigated.In fact the synergism can be described with molecular exchanging energy at the molecular structure level. The present work is divided into three parts: Firstly, based on the supposition that the mixed surfactants solution is also a regular solution just as Rubingh and Rosen supposed and with the helps of a two-dimensional crystal model and the Flory-Huggins lattice theory, a method of determining ε from β is developed. Secondly, another method of evaluating ε directly from the molecular structure of mixed surfactants with the Lennard-Jones formula is introduced. Finally, by using a common ani-

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“…This conclusion is also supported by our simulation results. Although most of the models on ionic surfactants assume a point unit charge at the headgroup or counterion, quantum chemical methods unveiled that the charge can partially distribute to the rest of the molecule, more significantly on the α-methylene group and less on the remaining alkyl chain [31]. This charge distribution has an important effect on surfactant self-assembly and can explain the polarity of micelle cores.…”

Section: Introductionmentioning

confidence: 99%

Effective short-range Coulomb correction to model the aggregation behavior of ionic surfactants

Burgos-Mármol

Solans

Patti

2016

The Journal of Chemical Physics

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We present a short-range correction to the Coulomb potential to investigate the aggregation of amphiphilic molecules in aqueous solutions. The proposed modification allows to quantitatively reproduce the distribution of counterions above the critical micelle concentration (CMC) or, equivalently, the degree of ionization, α, of the micellar clusters. In particular, our theoretical framework has been applied to unveil the behavior of the cationic surfactant C24H49N2O + 2 CH3SO − 4 , which offers a wide range of applications in the thriving and growing personal care market. A reliable and unambiguous estimation of α is essential to correctly understand many crucial features of the micellar solutions, such as their viscoelastic behavior and transport properties, in order to provide sound formulations for the above mentioned personal care solutions. We have validated our theory by performing extensive lattice Monte Carlo simulations, which show an excellent agreement with experimental observations. More specifically, our coarse-grained model is able to reproduce and predict the complex morphology of the micelles observed at equilibrium. Additionally, our simulation results disclose the existence of a transition from a monodisperse to a bidisperse size distribution of aggregates, unveiling the intriguing existence of a second CMC.

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Quantum-Chemical Calculations of the Charge Distribution in Ionic Surfactants

Cited by 108 publications

References 18 publications

Electronic structure computations of Newton Black Films

Electronic structure computations of Newton Black Films

Calculation of the molecular exchanging energy of binary surfactants system on the surface monolayer of aqueous solution

Effective short-range Coulomb correction to model the aggregation behavior of ionic surfactants

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