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Journal ArticleDOI

How strongly can calcium ion influence the hydrogen-bond dynamics at complex aqueous interfaces?

28 May 2007-Journal of Chemical Physics (American Institute of Physics)-Vol. 126, Iss: 20, pp 204710-204710
TL;DR: The author has performed three independent molecular dynamics computer simulations to examine the effects of counterion identity on hydrogen-bond dynamics in the enclosed water pool of anionic surfactant-based reverse micelles, indicating that there exists a strong competition between head group-counterion and headgroup-water interactions at such complex interfaces.
Abstract: The author has performed three independent molecular dynamics computer simulations to examine the effects of counterion identity on hydrogen-bond dynamics in the enclosed water pool of anionic surfactant-based reverse micelles. The water–water hydrogen-bond lifetime in the reverse micelle (RM) with calcium ions is found to be longer than that in the RM with sodium or ammonium ions. The hydrogen bond between a polar head group and a water molecule, on the other hand, breaks but reforms most rapidly in the RM with calcium ions, indicating that there exists a strong competition between head group–counterion and head group–water interactions at such complex interfaces.
Citations
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Journal ArticleDOI
TL;DR: In this article, the effect of interlayer cations on the preparation of 2D MMT nanosheets was investigated through atomic force microscopy (AFM) and molecular dynamics simulation for energy calculation.
Abstract: Montmorillonite (MMT) could be easily exfoliated into two-dimensional (2D) MMT nanosheets, leading to potential applications in many fields. In this work, the varying exfoliation properties of Na– and Ca–MMTs were investigated through atomic force microscopy (AFM) and molecular dynamics simulation for energy calculation in order to understand the effect of interlayer cations on the preparation of 2D MMT nanosheets. AFM results showed direct evidence that Na–MMT is easier to be exfoliated than Ca–MMT in the 2D nanosheet preparation. This observation was due to Ca–MMT having a higher interlayer binding energy (IBE) than Na–MMT because of the charge effect of the cations. Besides, the interaction energy between the water layer and two MMT layers (EW–M) of Na–MMTs was lower than that of Ca–MMTs at the same water content. In addition, it was found the exfoliated Ca–MMT had a larger particle diameter than that of exfoliated Na–MMT. These findings might be helpful for the preparation and application of 2D MMT nanosheets through controlling the exfoliation of MMT.

42 citations

Journal ArticleDOI
TL;DR: In this article, the effects of counterions on the properties of ionic surfactant systems in contact with aqueous solution phase are discussed, and three types of systems: normal micelles, monolayers at the air/aqueous solution interface, and reverse micella, i.e., water-in-oil microemulsions.
Abstract: Recent developments in the computer simulation studies of the effects of counterions on the properties of ionic surfactant systems in contact with aqueous solution phase are discussed. The article deals with three types of systems: normal micelles, monolayers at the air/aqueous solution interface, and reverse micelles, i.e., water-in-oil microemulsions.

34 citations

Journal ArticleDOI
TL;DR: The results revealed that the distinct nature of anion-water hydrogen bonded networks in the three systems was a key in modulating the observed unique density behaviour, and the differential nanostructuring affected the dynamics of the solutions proportionately.
Abstract: Ionic liquid/water binary mixtures are rapidly gaining popularity as solvents for dissolution of cellulose, nucleobases, and other poorly water-soluble biomolecules. Hence, several studies have focused on measuring the thermophysical properties of these versatile mixtures. Among these, 1-ethyl-3-methylimidazolium ([emim]) cation-based ILs containing different anions exhibit unique density behaviours upon addition of water. While [emim][acetate]/water binary mixtures display an unusual rise in density with the addition of low-to-moderate amounts of water, those containing the [trifluoroacetate] ([Tfa]) anion display a sluggish decrease in density. The density of [emim][tetrafluoroborate] ([emim][BF4])/water mixtures, on the other hand, declines rapidly in close accordance with the experimental reports. Here, we unravel the structural basis underlying this unique density behavior of [emim]-based IL/water mixtures using all-atom molecular dynamics (MD) simulations. The results revealed that the distinct nature of anion-water hydrogen bonded networks in the three systems was a key in modulating the observed unique density behaviour. Vast expanses of uninterrupted anion-water-anion H-bonded stretches, denoted here as anion-water wires, induced significant structuring in [emim][Ac]/water mixtures that resulted in the density rise. Conversely, the presence of intermittent large water clusters disintegrated the anion-water wires in [emim][Tfa]/water and [emim][BF4]/water mixtures to cause a monotonic density decrease. The differential nanostructuring affected the dynamics of the solutions proportionately, with the H-bond making and breaking dynamics found to be greatly retarded in [emim][Ac]/water mixtures, while it exhibited a faster relaxation in the other two binary solutions.

31 citations

Journal ArticleDOI
01 Jan 2022-Fuel
TL;DR: In this article , a comprehensive review of existing technologies, outline the gaps, potential, and required area for improvement of CO 2 thickeners in terms of their performance, cost-effectiveness and low ecological footprint.

25 citations

Journal ArticleDOI
TL;DR: Ion pairs are preferentially formed in confined RM systems, consistent with the well established ideas that RMs exhibit reduced polarity and a disrupted hydrogen bonding network compared to bulk water and that ion-specific effects are involved in mediating the structure of species at interfaces.
Abstract: Evidence for ion pair formation in aqueous bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelles (RMs) was obtained from infrared spectra of azide and cyanate with Li+, Na+, K+, and NH4+ counterions. The anions’ antisymmetric stretching bands near 2000 cm−1 are shifted to higher frequency (blueshifted) in LiAOT and to a lesser extent in NaAOT, but they are very similar to those in bulk water with K+ and NH4+ as the counterions. The shifts are largest for low values of wo=[water]/[AOT] and approach the bulk value with increasing wo. The blueshifts are attributed to ion pairing between the anions and the counterions. This interpretation is reinforced by the similar trend (Li+>Na+>K+) for producing contact ion pairs with the metal cations in bulk dimethyl sulfoxide (DMSO) solutions. We find no evidence of ion pairs being formed in NH4AOT RMs, whereas ammonium does form ion pairs with azide and cyanate in bulk DMSO. Studies are also reported for the anions in formamide-containing AOT RMs, in which blueshift...

18 citations

References
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Journal ArticleDOI
01 Jan 1996-Nature
TL;DR: In this paper, an interplay between diffusion and hydrogen-bond dynamics is proposed to explain the non-exponential kinetics of hydrogen bond formation and breaking in liquid water.
Abstract: HYDROGEN bonds play a crucial role in the behaviour of water1–4; their spatial patterns and fluctuations characterize the structure and dynamics of the liquid5–7. The processes of breaking and making hydrogen bonds in the condensed phase can be probed indirectly by a variety of experimental techniques8, and more quantitative information can be obtained from computer simulations9. In particular, simulations have revealed that on long timescales the relaxation behaviour of hydrogen bonds in liquid water exhibit non-exponential kinetics7,10–13, suggesting that bond making and breaking are not simple processes characterized by well defined rate constants. Here we show that these kinetics can be understood in terms of an interplay between diffusion and hydrogen-bond dynamics. In our model, which can be extended to other hydrogen-bonded liquids, diffusion governs whether a specific pair of water molecules are near neighbours, and hydrogen bonds between such pairs form and persist at random with average lifetimes determined by rate constants for bond making and breaking.

1,583 citations

Journal ArticleDOI
TL;DR: It is demonstrated that the long time dynamics of a single hydrogen bond in ambient liquid water is indeed characterized by significant nonexponential relaxation, and this complex relaxation is essentially uncorrelated to the specific bonding patterns near the tagged hydrogen bond.
Abstract: In a series of molecular dynamics calculations we simulate the dynamics of forming and breaking a hydrogen bond in liquid water at room temperature. We show that this dynamics is clearly nonexponential, yet virtually uncorrelated with the fluctuations of neighboring bonds.

947 citations

Journal ArticleDOI
19 Sep 2003-Science
TL;DR: Using simulations of an atomistic model of water, this work relates frequency fluctuations in the OH-stretching frequency of HOD in liquid D2O with femtosecond infrared spectroscopy to intermolecular dynamics.
Abstract: We investigated rearrangements of the hydrogen-bond network in water by measuring fluctuations in the OH-stretching frequency of HOD in liquid D2O with femtosecond infrared spectroscopy. Using simulations of an atomistic model of water, we relate these frequency fluctuations to intermolecular dynamics. The model reveals that OH frequency shifts arise from changes in the molecular electric field that acts on the proton. At short times, vibrational dephasing reflects an underdamped oscillation of the hydrogen bond with a period of 170 femtoseconds. At longer times, vibrational correlations decay on a 1.2-picosecond time scale because of collective structural reorganizations.

896 citations

Journal ArticleDOI
02 Feb 1996-Science
TL;DR: In this article, the protein bovine serum albumin (BSA) with a molecular weight of 67,000 is soluble in a carbon dioxide-continuous phase with a nontoxic ammonium carboxylate perfluoropolyether surfactant.
Abstract: Carbon dioxide in the liquid and supercritical fluid states is useful as a replacement for toxic organic solvents. However, nonvolatile hydrophilic substances such as proteins, ions, and most catalysts are insoluble. This limitation was overcome by the formation of aqueous microemulsion droplets in a carbon dioxide-continuous phase with a nontoxic ammonium carboxylate perfluoropolyether surfactant. Several spectroscopic techniques consistently indicated that the properties of the droplets approach those of bulk water. The protein bovine serum albumin (BSA) with a molecular weight of 67,000 is soluble in this microemulsion and experiences an environment similar to that of native BSA in buffer.

542 citations