Insight into the Hydration of Cationic Surfactants: A Thermodynamic and Dielectric Study of Functionalized Quaternary Ammonium Chlorides

Medoš, Žiga; Plechkova, Natalia V.; Friesen, Sergej; Buchner, Richard; Bešter‐Rogač, Marija

doi:10.1021/acs.langmuir.8b03993

Cited by 24 publications

(14 citation statements)

References 67 publications

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“…The strong interaction between the hydroxyl group and water molecules supplements our understanding of why the quat-10-OH molecules do not form micelles. Reduction in the aggregation number of micelle upon substitution of a methyl group with a polar functional group is also observed experimentally by Medoš et al…”

Section: Resultssupporting

confidence: 69%

Understanding the Hydration Thermodynamics of Cationic Quaternary Ammonium and Charge-Neutral Amine Surfactants

Singh

Sharma

2022

J. Phys. Chem. B

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Aqueous solubility and interfacial adsorption of surfactants are important for numerous applications. Using molecular dynamics, we have studied the effect of the type of the polar headgroup (cationic quaternary ammonium and charge-neutral amine) and length of the alkyl tail on the hydration free energy of surfactants in infinite dilution. In addition, we have studied the effect of replacing the terminal methyl group of the alkyl tail with a more polar hydroxyl group on the hydration free energy. Quaternary ammonium surfactants have strongly favorable hydration free energies, whereas charge-neutral amine surfactants have unfavorable hydration free energies. The contribution of the quaternary ammonium group in reducing the hydration free energy is estimated to be as large as ∼63 k B T and that of the charge-neutral amine group to be 3 k B T. Both surfactants and their corresponding alkanes have minima in the free energy at the air−water interface. The quaternary ammonium group contributes to a 6 k B T decrease in the free energy of transfer from air−water interface to bulk aqueous phase (termed henceforth as interface transfer free energy). The amine group, on the other hand, has a net zero interface transfer free energy. The interface transfer free energies of surfactants are both enthalpically and entropically unfavorable. The enthalpic penalty is attributed to the loss of water−water interactions. Interestingly, surfactant molecules gain entropy upon their transfer from the air−water interface to the aqueous phase, but this increase is more than compensated by the loss in the entropy of water molecules, presumably due to the ordering of water molecules around the surfactants. Replacing the terminal methyl group of the alkyl tail with a hydroxyl group in quat surfactants reduces their hydration free energy by 10 k B T, thus making them more soluble in water. Attaching a hydroxyl group to the alkyl tail also inhibits their micelle forming tendency in the bulk aqueous phase. Overall, this work reveals how tuning the molecular characteristics of surfactants can help to achieve the desirable aqueous solubility, interfacial properties, and micellization tendency of surfactants.

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Section: Resultssupporting

confidence: 69%

Understanding the Hydration Thermodynamics of Cationic Quaternary Ammonium and Charge-Neutral Amine Surfactants

Singh

Sharma

2022

J. Phys. Chem. B

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“…While the underlying cause of these frequency shifts is yet to be fully explored, they are ascribed here as arising from inductive effects. It is well established that alkyl groups are electron donating via the inductive effect, − and it is this electron donation from the adjacent methyl groups to the head group nitrogen that shifts their C–H stretching modes to higher frequencies relative to those of the methyl along the alkyl tail. − Furthermore, in sp 3 -hybridized quaternary ammonium cations (such as the nitrogen of the CTAB head group), the positive charge is distributed among the methyl hydrogen atoms. ,− This creates the potential for what is referred to as an “improper” hydrogen bond that forms between the methyl hydrogen and an electron lone pair on water (CH···O H-bond). ,,− ,− Interestingly, for such sp 3 -hybridized central atoms, this sort of improper hydrogen bond yields a bond contraction, causing the C–H modes to shift to even higher frequencies. ,,,,,,, A full discussion of the solvation environment of CTAB is complex − and beyond the scope of this work. Instead, an overview description of what has been found in these previous studies is given in the Supporting Information.…”

Section: Results and Discussionmentioning

confidence: 99%

Takes Two to Tango: Choreography of the Coadsorption of CTAB and Hexanol at the Oil–Water Interface

et al. 2019

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Mixed surfactant systems at the oil–water interface play a vital role in applications ranging widely from drug delivery to oil-spill remediation. Synergistic mixtures are superior emulsifiers and more effective at modifying surface tension than either component alone. Mixtures of surfactants with dissimilar polar head groups are of particular interest because of the additional degree of control they offer. The interplay of hydrophobic and electrostatic effects in these systems is not well understood, in part because of the difficulty in examining their behavior at the buried oil–water interface where they reside. Here, surface-specific vibrational sum frequency spectroscopy is utilized in combination with surface tensiometry and computational methods to probe the cooperative molecular interactions between a cationic surfactant cetyltrimethylammonium bromide (CTAB) and a nonionic alcohol (1-hexanol) that induce the two initially reluctant surfactants to coadsorb synergistically at the interface. A careful deuteration study of CTAB reveals that hexanol cooperates with CTAB such that both molecules preferentially orient at the interface for sufficiently large enough concentrations of hexanol. This work’s methodology is unique and serves as a guide for future explorations of macroscopic properties in these complex systems. Results from this work also provide valuable insights into how interfacial ordering impacts surface tensiometry measurements for nonionic surfactants.

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“…We also note that the initial water-to-glycine mole ratios were higher for AN + GC particles (6) than SN + GC particles (2), and sodium has a higher hydration number (6; Medoš et al, 2019) than ammonium (4; Guo et al, 2020). Therefore, the availability of free water in AN + GC particles is likely higher than in SN + GC particles.…”

Section: Nitrate Photochemistry Of An + Gc and Sn + Gc Particlesmentioning

confidence: 81%

Distinct photochemistry in glycine particles mixed with different atmospheric nitrate salts

Liang,

Cheng,

Zhang

et al. 2023

Atmos. Chem. Phys.

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Abstract. Particulate free amino acids (FAAs) are essential components of organonitrogen that have critical climate impacts, and they are usually considered stable end-products from protein degradation. In this work, we investigated the decay of glycine (GC) as a model FAA under the photolysis of different particulate nitrate salts using an in situ Micro-Raman system. Upon cycling the relative humidity (RH) between 3 % and 80 % RH, ammonium nitrate (AN) and GC mixed particles did not exhibit any phase change, whereas sodium nitrate (SN) and GC mixed particles crystallized at 60 % and deliquesced at 82 % RH. Under light illumination at 80 % RH, AN + GC particles showed almost no spectral changes, while rapid decays of glycine and nitrate were observed in SN + GC particles. The interactions between nitrate and glycine in AN + GC particles suppressed crystallization but also hindered nitrate photolysis and glycine decay. On the other hand, glycine may form a complex with Na+ in deliquescent SN + GC particles and allow unbonded nitrate to undergo photolysis and trigger glycine decay, though nitrate photolysis was greatly hindered upon particle crystallization. Our work provides insights into how FAAs may interact with different nitrate salts under irradiation and lead to distinct decay rates, which facilitates their atmospheric lifetime estimation.

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Insight into the Hydration of Cationic Surfactants: A Thermodynamic and Dielectric Study of Functionalized Quaternary Ammonium Chlorides

Cited by 24 publications

References 67 publications

Understanding the Hydration Thermodynamics of Cationic Quaternary Ammonium and Charge-Neutral Amine Surfactants

Understanding the Hydration Thermodynamics of Cationic Quaternary Ammonium and Charge-Neutral Amine Surfactants

Takes Two to Tango: Choreography of the Coadsorption of CTAB and Hexanol at the Oil–Water Interface

Distinct photochemistry in glycine particles mixed with different atmospheric nitrate salts

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