A visualized analysis of small-angle neutron scattering intensity: concentration fluctuation in alcohol–water mixtures

Misawa, Masakatsu; Satô, Tôru; Onozuka, A.; Maruyama, Kenji; Mori, Kazuhiro; Suzuki, S.; Otomo, Toshiya

doi:10.1107/s0021889807001549

Cited by 10 publications

(8 citation statements)

References 12 publications

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“…We note that the very small k behavior determined by our simulations is uncertain for the reasons discussed above, and the experiments do not extend to values of k low enough to determine the behavior as k → 0. We do note that SANS results reported by Misawa et al 15 do not appear to show the presence of a prepeak at very low k. Finally, we note that, due to large cancellations amongst the structure factors occuring on in Eq. 2, the absence of a prepeak in the experimentally measured total scattering, I(k), does not rule out the possibility of domain-related prepeaks in the atom-atom structure factors S…”

Section: B Structure Factorscontrasting

confidence: 45%

“…We show that over the measured region, our simulation results are in good agreement with SAXS and SANS experiments. 15,23 The remainder of this paper is organized as follows. The models and simulation details are discussed in Section II, simulation results are described and compared with experiment in Section III, and our conclusions are summarized in Section IV.…”

Section: Introductionmentioning

confidence: 99%

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Structural behavior of aqueous t-butanol solutions from large-scale molecular dynamics simulations

Overduin

Perera

Patey

2019

The Journal of Chemical Physics

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Large-scale molecular dynamics (MD) simulations are reported for aqueous t-butanol (TBA) solutions. The CHARMM generalized force field (CGenFF) for TBA is combined with the TIP4P/2005 model for water. Unlike many other common TBA models, the CGenFF model is miscible with water in all proportions at 300 K. The main purpose of this work is to investigate the existence and nature of microheterogeneous structure in aqueous TBA solutions. Our simulations of large systems (128000 and 256000 particles) at TBA mole fractions of 0.06 and 0.1 clearly reveal the existence of long-range correlations (> 10 nm) that show significant variations on long time scales (∼ 50 ns). We associate these long-range, slowly varying correlations with the existence of supramolecular, domain-like structures that consist of TBA-rich and water-rich regions. This structure is always present but continually changing in time, giving rise to long-range, slowly varying pair correlation functions. We find that this behavior appears to have little influence on the single particle dynamics; the diffusion coefficients of both TBA and water molecules lie in the usual liquid state regime, and mean square displacements provide no indication of anomalous diffusion. Using our large system simulations, we are able to reliably calculate small angle x-ray scattering (SAXS) and small angle neutron scattering (SANS) spectra, except at very low wave vector, and the results agree well with recent experiments. However, the present paper shows that simulation of the relatively simple TBA/water system remains challenging. This is particularly true if one wishes to obtain properties such as Kirkwood-Buff factors, or scattering functions at low wave vector, which strongly depend on the long-range behavior of the pair correlations.

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Section: B Structure Factorscontrasting

confidence: 45%

Section: Introductionmentioning

confidence: 99%

Structural behavior of aqueous t-butanol solutions from large-scale molecular dynamics simulations

Overduin

Perera

Patey

2019

The Journal of Chemical Physics

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“…1,2 However, recent experimental and computational studies show that they are inhomogeneous over smaller length scales. Molecular-scale "clusters" (order of 1 nm in size) [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] and, occasionally, mesoscale structures (order of 100 nm in size) [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] have been reported in such aqueous solutions.…”

Section: Introductionmentioning

confidence: 99%

“…[41][42][43] However, nonionic hydrotropes may show the presence of a dynamic, loose noncovalent "clustering" akin to "micelle-like structural uctuations". [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] Such uctuations can be detected from molecular dynamics simulations 8,9,[12][13][14][15][16][17][18][19][20][21] and neutron spin echo experiments. 7 The molecular clusters have a size of the order of 1 nm and a lifetime of tens of picoseconds.…”

Section: Introductionmentioning

confidence: 99%

Mesoscale inhomogeneities in aqueous solutions of small amphiphilic molecules

et al. 2013

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Small amphiphilic molecules, also known as hydrotropes, are too small to form micelles in aqueous solutions. However, aqueous solutions of nonionic hydrotropes show the presence of a dynamic, loose, non-covalent clustering in the water-rich region, This clustering can be viewed as "micelle-like structural fluctuations". Although these fluctuations are short ranged (approximately 1 nm) and short lived (10 ps-50 ps), they may lead to thermodynamic anomalies. In addition, many experiments on aqueous solutions of hydrotropes show the occasional presence of mesoscale (approximately 100 nm) inhomogeneities. We have combined results obtained from molecular dynamics simulations, small-angle neutron scattering, and dynamic light-scattering experiments carried out on tertiary butyl alcohol (hydrotrope)-water solutions and on tertiary butyl alcohol-water-cyclohexane (hydrophobe) solutions to elucidate the nature and structure of these inhomogeneities. We have shown that stable mesoscale inhomogeneities occur in aqueous solutions of nonionic hydrotropes only when the solution contains a third, more hydrophobic, component. Moreover, these inhomogeneities exist in ternary systems only in the concentration range where structural fluctuations and thermodynamic anomalies are observed in the binary water-hydrotrope solutions. Addition of a hydrophobe seems to stabilize the water-hydrotrope structural fluctuations, and leads to the formation of larger (mesoscopic) droplets. The structure of these mesoscopic droplets is such that they have a hydrophobe-rich core, surrounded by a hydrogen-bonded shell of water and hydrotrope molecules. These droplets can be extremely long-lived, being stable for over a year. We refer to the phenomenon of formation of mesoscopic droplets in aqueous solutions of nonionic hydrotropes containing hydrophobes, as mesoscale solubilization. This phenomenon may represent a ubiquitous feature of nonionic hydrotropes that exhibit clustering in water, and may have important practical applications in areas, such as drug delivery, where the replacement of traditional surfactants may be necessary.

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“…Literature indicating large scale inhomogeneities in aqueous solutions is accumulating, with emphasis on static and dynamic laser light scattering (LLS) measurements [69][70][71][72][73][74][75][76][77][78][79][80]. A wide variety of other experimental techniques may confirm that in aqueous under-saturated strong electrolyte solutions, the ions are not homogeneously distributed [63,[81][82][83][84][85][86]. Quantum electrodynamic interactions may cause formation of μm-sized domains composed of solvated ions [87][88][89][90].…”

Section: Large-scale Inhomogeneities In Aqueous Systems And/or Exclusmentioning

confidence: 99%

Possible Further Evidence for the Thixotropic Phenomenon of Water

Verdel

Bukovec

2014

Entropy

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Abstract:In this work we review the literature for possible confirmation of a phenomenon that was proposed to develop when water is left to stand for some time undisturbed in closed vessels. The phenomenon has been termed thixotropy of water due to the weak gel-like behaviour which may develop spontaneously over time where ions and contact with hydrophilic surfaces seem to play important roles. Thixotropy is a property of certain gels and liquids that under normal conditions are highly viscous, whereas during mechanical processing their viscosity diminishes. We found experiments indicating water's self-organizing properties, long-lived inhomogeneities and time-dependent changes in the spectral parameters of aqueous systems. The large-scale inhomogeneities in aqueous solutions seem to occur in a vast number of systems. Long-term spectral changes of aqueous systems were observed even though the source of radiation was switched off or removed. And water was considered to be an active excitable medium in which appropriate conditions for self-organization can be established. In short, the thixotropic phenomenon of water is further indicated by different experimental techniques and may be triggered by large-scale ordering of water in the vicinity of nucleating solutes and hydrophilic surfaces.

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A visualized analysis of small-angle neutron scattering intensity: concentration fluctuation in alcohol–water mixtures

Cited by 10 publications

References 12 publications

Structural behavior of aqueous t-butanol solutions from large-scale molecular dynamics simulations

Structural behavior of aqueous t-butanol solutions from large-scale molecular dynamics simulations

Mesoscale inhomogeneities in aqueous solutions of small amphiphilic molecules

Possible Further Evidence for the Thixotropic Phenomenon of Water

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