Probing the Molecular Orientation of Methyl Isobutyl Carbinol at the Air–Water Interface

Nguyen, Khoi Tan; Shahir, Afshin Asadzadeh; Nguyen, Anh V.

doi:10.1007/s11743-017-1976-2

Cited by 10 publications

(6 citation statements)

References 30 publications

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“…A recent study in our group [144] showed that MIBC has an ignorable degree of overall molecular orientation change within quite a wide concentration range, so it may be suitable to assign similar values to the maximum and minimum surface areas used in the orientation models. In addition, some researchers [145,146] even proposed a Langmuir form double-…”

Section: Accepted Manuscript 50mentioning

confidence: 99%

A critical review of the model fitting quality and parameter stability of equilibrium adsorption models

Peng

Nguyen

Wang

et al. 2018

Advances in Colloid and Interface Science

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We reviewed eight commonly used equilibrium adsorption models and examined their underlying assumptions, fitting qualities, and parameter stabilities. We compared several objective functions that have been applied to curve fitting analysis and a few statistics tests that have been performed to evaluate regression quality. The iteratively reweighted least squares algorithm was selected as the most suitable regression method for adsorption models in the presence of heteroscedasticity. The fraction of unexplained variance was selected to indicate the model fitting quality. Two sources of parameter instability were identified: residue instability and function instability. While the definition of the instability caused by residue is well established, we are the first to consider the instability caused by an adsorption model. The models discussed in this article can be applied to many surfactants, such as normal alcohols, polyglycol ethers, and sodium dodecyl sulfate at different salt concentrations. Our results show that both the model fitting quality and parameter instability increase with the number of parameters subject to curve fitting. For the Frumkin-type of reorientation model, the parameter instability can be as high as 25%. The high degree of instability in some complicated adsorption models may invalidate the estimated parameters.Therefore, additional measurements or simulations are required for complicated models to extract reliable model parameters.

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Section: Accepted Manuscript 50mentioning

confidence: 99%

A critical review of the model fitting quality and parameter stability of equilibrium adsorption models

Peng

Nguyen

Wang

et al. 2018

Advances in Colloid and Interface Science

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“…This alcohol forms a highly ordered layer of molecular dipoles which creates a moderate electric potential at the water surface. 29 This enabled us to identify a remarkable specific screening effect of cations on the surface potential. In the second step, the SFG spectra for the solutions of LiCl, NaCl, and CsCl with concentrations ranging from low (50 mM and 0.5 M) to medium (2 M) were recorded in the OH stretch region, that is, 3000−3800 cm −1 .…”

Section: Introductionmentioning

confidence: 99%

Combined Sum Frequency Generation and Thin Liquid Film Study of the Specific Effect of Monovalent Cations on the Interfacial Water Structure

et al. 2018

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Some salts have been recently shown to decrease the sum frequency generation (SFG) intensity of the hydrogen-bonded water molecules, but a quantitative explanation is still awaited. Here, we report a similar trend for the chloride salts of monovalent cations, that is, LiCl, NaCl, and CsCl, at low concentrations. Specifically, we revealed not only the specific adsorption of cations at the water surface but also the concentration-dependent effect of ions on the SFG response of the interfacial water molecules. Our thin-film pressure balance (TFPB) measurements (stabilized by 10 mM of methyl isobutyl carbinol) enabled the determination of the surface potential that governs the surface electric field affecting interfacial water dipoles. The use of the special alcohol also enabled us to identify a remarkable specific screening effect of cations on the surface potential. We explained the concentration dependency by considering the direct ion-water interactions and water reorientation under the influence of surface electric field as the two main contributors to the overall SFG signal of the hydrogen-bonded water molecules. Although the former was dominant only at the low-concentration range, the effect of the latter intensified with increasing salt concentration, leading to the recovery of the band intensity at medium concentrations. We discussed the likelihood of a correlation between the effect of ions on reorientation dynamics of water molecules and the broad-band intensity drop in the SFG spectra of salt solutions. We proposed a mechanism for the cation-specific effect through the formation of an ionic capacitance at the solution surface. It explains how cations could impart the ion specificity while they are traditionally believed to be repelled from the interfacial region. The electrical potential of this capacitance varies with the charge separation and ion density at the interface. The charge separation being controlled by the polarizability difference between anions and cations was identified using the SFG response of the interfacial water molecules as an indirect probe. The ion density being affected by the absolute polarizability of ions was tracked through the measurement of the surface potentials and Debye-Hückel lengths using the TFPB technique.

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“…For example, the equilibrium constant and the maximum surface excess can be determined experimentally. − Also, Monte Carlo (MC) simulation can be used to calculate the surface areas of molecules such as poly(glycol ethers) and SDS. , Molecular dynamics (MD) was also used to quantify the surfactant adsorption. − Those methods significantly reduced the number of adjustable parameters, which would increase the model stability. It is worth mentioning that sum-frequency generation spectroscopy (SFG) can be used to determine the orientation angle of surfactant molecules. − It may seem straightforward that the classical curve-fitting method can be combined with additional techniques to reveal the mystery of surfactant adsorption. However, those techniques produce very different results, and there is no way to determine which result is more realistic.…”

Section: Problems Of Classical Theories In Comparison With Experimentsmentioning

confidence: 99%

“…We explain this by introducing an additional surfactant adsorption layer. At high concentration, even the surface monolayer is already saturated, and the under-monolayer region still provides adsorption sites for MIBC molecules. , The under-monolayer region is not detectable by SFG because this technique is highly interfacially specific. However, surfactant molecules adsorbed in this region still contribute to the total surface excess as observed by the surface tension drop.…”

Section: Problems Of Classical Theories In Comparison With Experimentsmentioning

confidence: 99%

From Surface Tension to Molecular Distribution: Modeling Surfactant Adsorption at the Air–Water Interface

et al. 2021

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Surfactants are centrally important in many scientific and engineering fields and are used for many purposes such as foaming agents and detergents. However, many challenges remain in providing a comprehensive understanding of their behavior. Here, we provide a brief historical overview of the study of surfactant adsorption at the air−water interface, followed by a discussion of some recent advances in this area from our group. The main focus is on incorporating an accurate description of the adsorption layer thickness of surfactant at the air−water interface. Surfactants have a wide distribution at the air−water interface, which can have a significant effect on important properties such as the surface excess, surface tension, and surface potential. We have developed a modified Poisson−Boltzmann (MPB) model to describe this effect, which we outline here. We also address the remaining challenges and future research directions in this area. We believe that experimental techniques, modeling, and simulation should be combined to form a holistic picture of surfactant adsorption at the air−water interface.

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Probing the Molecular Orientation of Methyl Isobutyl Carbinol at the Air–Water Interface

Cited by 10 publications

References 30 publications

A critical review of the model fitting quality and parameter stability of equilibrium adsorption models

A critical review of the model fitting quality and parameter stability of equilibrium adsorption models

Combined Sum Frequency Generation and Thin Liquid Film Study of the Specific Effect of Monovalent Cations on the Interfacial Water Structure

From Surface Tension to Molecular Distribution: Modeling Surfactant Adsorption at the Air–Water Interface

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