Sodium diffusion through amorphous silica surfaces: A molecular dynamics study

Rarivomanantsoa, M.; Jund, Philippe; Jullien, R.

doi:10.1063/1.1645511

Cited by 12 publications

(7 citation statements)

References 62 publications

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“…During shear deformation, the network modifier (Na atoms) appears to be the most mobile atomic species, followed by oxygen and silicon atoms. This order respects as well the mobility observed by thermal activation [71][72][73]. It appears that reducing the free volume in the structure (by compressing the samples) reduces the global mobility of the atoms.…”

Section: A Nonaffine Displacementssupporting

confidence: 68%

Effect of composition and pressure on the shear strength of sodium silicate glasses: An atomic scale simulation study

2017

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The elastoplastic behavior of sodium silicate glasses is studied at different scales as a function of composition and pressure, with the help of quasistatic atomistic simulations. The samples are first compressed and then sheared at constant pressure to calculate yield strength and permanent plastic deformations. Changes occurring in the global response are then compared to the analysis of local plastic rearrangements and strain heterogeneities. It is shown that the plastic response results from the succession of well-identified localized irreversible deformations occurring in a nanometer-size area. The size and the number of these local rearrangements, as well as the amount of internal deviatoric and volumetric plastic deformation, are sensitive to the composition and to the pressure. In the early stages of the deformation, plastic rearrangements are driven by sodium mobility. Consequently, the elastic yield strength decreases when the sodium content increases, and the same when pressure increases. Finally, good correlation was found between global and local stress-strain relationships, reinforcing again the role of sodium ions as local initiators of the plastic behavior observed at larger scales.

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Section: A Nonaffine Displacementssupporting

confidence: 68%

Effect of composition and pressure on the shear strength of sodium silicate glasses: An atomic scale simulation study

2017

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“…Above 300°C, a loss of NBO with a consequent increase in BO is detected; this could be attributed to the condensation of NBOs to BO upon desorption of modifier ions (Figure A). While a loss in NBO is observed on the unleached surface, there is an increase in NBO on the leached surface due to out‐diffusion of sodium (Figure B) . The formation of new NBO sites on the leached glass due to sodium out‐diffusion is not explicitly evident in the O 1s spectrum of the leached glass at 500°C in Figure because its quantity is so small.…”

Section: Resultsmentioning

confidence: 94%

“…| 649 diffusion of sodium ( Figure 2B). 26,27 The formation of new NBO sites on the leached glass due to sodium out-diffusion is not explicitly evident in the O 1s spectrum of the leached glass at 500°C in Figure 3 because its quantity is so small. Other researchers have shown that sodium inclusion into a silica network results in creation of NBO sites similar to those in sodium silicate glasses.…”

Section: Xps Quantificationmentioning

confidence: 99%

Effect of heat treatment on the surface chemical structure of glass: Oxygen speciation from in situ XPS analysis

et al. 2017

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Compositional changes in unleached and acid‐leached soda‐lime silicate surfaces were tracked with in‐vacuo heating and X‐ray Photoelectron Spectroscopy. Surface oxygen speciation was determined using a stoichiometry‐based algorithm via elemental composition, instead of the typical O 1s peak‐fitting approach. Accurate surface hydroxyl quantification is shown to require dehydration at temperatures near 200°C. On the unleached surface, no change in surface hydroxyl density (~2.5 OH/nm2) is observed in the temperature range of 200°C‐500°C after the initial dehydration. However, repolymerization in the network (non‐bridging oxygen→bridging oxygen) is observed due to volatilization of sodium. The acid‐leached surface undergoes sodium out‐diffusion from the bulk at sub‐Tg temperatures with laterally resolved inhomogeneity and shows a reduction in the concentration of hydroxyls from 4.5 OH/nm2 (200°C) to 3.2 OH/nm2 (500°C) accompanied by an increase in bridging oxygen. These results suggest that when [OH] > 2.5~3/nm2, vicinal OH undergo dehydroxylation with evolution of water, whereas when [OH] < 2.5/nm2, most OHs are non‐interacting and isolated (at temperatures below Tg). Furthermore, at temperatures exceeding 300°C, sodium has enough thermal energy to desorb in vacuum and diffuse from the bulk (depending on the abundance & local structure).

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“…46,47 In other words, lithium ions are more susceptible to diffuse toward the nearest most constrained Si− O−Si bonds, which are the most reactive sites in the silica network, than Na + and K + ions. 48 However, diffusion parameters are not the only ones to be taken into account. Indeed, Mazzara et al well described that creation of a nonbridging oxygen is accompanied by the rearrangement of silica tetrahedra surrounding the diffusing ion in a defined stereochemical order, 49 highlighting that relaxation of the amorphous silica network around the ion and finally the film densification is the combination of the creation of nonbridging oxygen atoms and also the steric effect of the diffusing cations.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…46,47 In other words, lithium ions are more susceptible to diffuse toward the nearest most constrained Si-O-Si bonds, which are the most reactive sites in the silica network, than Na + and K + ions. 48 However diffusion parameters are not the only ones to take into account. Indeed Mazzara et al well described that creation of a nonbridging oxygen is accompanied by the rearrangement of silica tetrahedra surrounding the diffusing ion in a defined stereochemical order.…”

Section: ) Sio 2 Mesopore Reconstruction Using Lithium or Potassium Ionsmentioning

confidence: 99%

Engineering of Silica Thin-Film Nanoporosity via Alkali-Ion-Assisted Reconstruction

et al. 2019

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We report a method to prepare patterned mesoporous silica-based films with a fine control of the pore sizes and the porous fraction by combining the sol gel approach with an alkali ion posttreatment. Strategy involves the porous mesostructure reconstruction of surfactant (CTAB or F127) templated silica films by alkali metal ions diffusion into the inorganic matrix at 450°C. Coatings with pores ranged from 2 nm to 100 nm, gradient of pore sizes and porous volumes as well as 2D patterned structures were obtained by optimizing the alkali ions assisted reconstruction process (alkali ions amount, liquid deposition techniques, …). Na + , Li + and K + are demonstrated as efficient silica network modifiers to significantly and rapidly tailor the mesostructure of the film. Using spectroscopic ellipsometry, SEM, environmental ellipsometry porosimetry, atomic absorption spectroscopy, and phase diagram simulations, two different alkali ions-induced mechanisms were identified: the densification of the silica framework and the separation in two phases of the silica matrix. Both mechanisms are easily controlled separately by adjusting the process conditions and the kind of ions used. This study, with the demonstration of an adaptive multi-responsive antireflective coating, shows that alkali ions assisted pore restructuration is complementary to the existing sol gel techniques and is promising for the design of new functional smart materials. Introduction:Synergic coupling between liquid-phase sol gel chemistry that permits to fashion inorganic or hybrid materials in particles, thin films, monoliths, membranes etc. [1][2][3][4] and self-assembled amphiphilic molecule mesophases 5,6 has given birth to an important class of nanostructured materials with potential applications in various fields such as catalysis and separation, drug delivery, optics, sensing, stimuli responsive materials, and so forth. [7][8][9][10][11][12][13] In such combination, micellar and lyotropic liquid-crystal phases act as a scaffold around which sol gel precursors condense, generating mesoporous materials after the elimination of the structuring agents. According to the nature of the surfactant template (divided in two main families: amphiphilic block copolymers and ionic or nonionic surfactants) and the synthesis conditions, the inorganic or hybrid porous materials can exhibit various well controlled 2D or 3D periodically ordered mesostructures (i.e. disorganized, worm-like, hexagonal and cubic symmetries) and diverse pore size distributions commonly comprised between 2 nm and tens of nanometers. For instance, cetyltrimethylammonium bromide (CTAB) is a well-known ionic surfactant forming ca. 2 nm pore sizes, while Pluronic F127 (EO 106 PO 70 EO 106 ) triblock copolymer is routinely used to reach pore sizes up to about 8 nm. 14,15

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Sodium diffusion through amorphous silica surfaces: A molecular dynamics study

Cited by 12 publications

References 62 publications

Effect of composition and pressure on the shear strength of sodium silicate glasses: An atomic scale simulation study

Effect of composition and pressure on the shear strength of sodium silicate glasses: An atomic scale simulation study

Effect of heat treatment on the surface chemical structure of glass: Oxygen speciation from in situ XPS analysis

Engineering of Silica Thin-Film Nanoporosity via Alkali-Ion-Assisted Reconstruction

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