Diffusion of Simple Liquids in Porous Sol-Gel Glass

Koone, Neil D.; Shao, Y.; Żerda, T. W.

doi:10.1021/j100046a025

Cited by 66 publications

(68 citation statements)

References 7 publications

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“…[32][33][34][35][36][37][38][39] In addition, the reorientational and diffusional dynamics are slowed, often dramatically. 10,[39][40][41][42][43][44][45][46][47][48][49] The effect of nanoscale confinement on water is more limited to the interfacial region compared to other liquids despite the fact that it is a networked liquid. 22,39,46,47 This can primarily be attributed to the absence in water of steric effects that propagate the constraints of the confining surface to larger distances in other liquids.…”

Section: Introductionmentioning

confidence: 99%

Simulations of the infrared, Raman, and 2D-IR photon echo spectra of water in nanoscale silica pores

Burris

Laage

Thompson

2016

The Journal of Chemical Physics

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Vibrational spectroscopy is frequently used to characterize nanoconfined liquids and probe the effect of the confining framework on the liquid structure and dynamics relative to the corresponding bulk fluid. However, it is still unclear what molecular-level information can be obtained from such measurements. In this paper, we address this question by using molecular dynamics (MD) simulations to reproduce the linear infrared (IR), Raman, and two-dimensional IR (2D-IR) photon echo spectra for water confined within hydrophilic (hydroxyl-terminated) silica mesopores. To simplify the spectra the OH stretching region of isotopically dilute HOD in D 2 O is considered. An empirical mapping approach is used to obtain the OH vibrational frequencies, transition dipoles, and transition polarizabilities from the MD simulations. The simulated linear IR and Raman spectra are in good general agreement with measured spectra of water in mesoporous silica reported in the literature. The key effect of confinement on the water spectrum is a vibrational blueshift for OH groups that are closest to the pore interface. The blueshift can be attributed to the weaker hydrogen bonds (H-bonds) formed between the OH groups and silica oxygen acceptors. Non-Condon effects greatly diminish the contribution of these OH moieties to the linear IR spectrum, but these weaker H-bonds are readily apparent in the Raman spectrum. The 2D-IR spectra have not yet been measured and thus the present results represent a prediction. The simulated spectra indicates that it should be possible to probe the slower spectral diffusion of confined water compared to the bulk liquid by analysis of the 2D-IR spectra. Published by AIP Publishing. [http://dx

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Section: Introductionmentioning

confidence: 99%

Simulations of the infrared, Raman, and 2D-IR photon echo spectra of water in nanoscale silica pores

Burris

Laage

Thompson

2016

The Journal of Chemical Physics

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“…We are unaware of any measurements of the diffusion constants of large solutes such as C153 in nanoconfined solvents (though such results would be a welcome addition to the literature). However, self-diffusion constants of a variety of liquids in nanoscale silica pores have been reported to be smaller by factors of 3.7-8.2 compared to the bulk liquid, 43 which hints at even greater slowing of large solute mobility. Similarly, molecular reorientation is dramatically slowed in silica pores, often by as much as an orderof-magnitude or more.…”

Section: Additional Considerationsmentioning

confidence: 99%

Solute location in a nanoconfined liquid depends on charge distribution

Harvey

Thompson

2015

The Journal of Chemical Physics

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Nanostructured materials that can confine liquids have attracted increasing attention for their diverse properties and potential applications. Yet, significant gaps remain in our fundamental understanding of such nanoconfined liquids. Using replica exchange molecular dynamics simulations of a nanoscale, hydroxyl-terminated silica pore system, we determine how the locations explored by a coumarin 153 (C153) solute in ethanol depend on its charge distribution, which can be changed through a charge transfer electronic excitation. The solute position change is driven by the internal energy, which favors C153 at the pore surface compared to the pore interior, but less so for the more polar, excited-state molecule. This is attributed to more favorable non-specific solvation of the large dipole moment excited-state C153 by ethanol at the expense of hydrogen-bonding with the pore. It is shown that a change in molecule location resulting from shifts in the charge distribution is a general result, though how the solute position changes will depend upon the specific system. This has important implications for interpreting measurements and designing applications of mesoporous materials. C 2015 AIP Publishing LLC. [http://dx

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“…Though Al co-doping consistently correlates with lower density, the effect of Al co-doping on the intensity of ET peaks is not yet fully understood. Using alternative immersion solution solvents could provide additional information, as water is known to adsorb on the internal pore surfaces of the sol-gel glass by hydrogen bonding with remaining silanols [17]. Re-heating procedures using a range of temperatures are also being explored.…”

Section: Conclusion and Further Investigationmentioning

confidence: 99%