Concentration-Dependent Self-Diffusion of Water in Aqueous Solutions of Lithium Chloride Confined to Porous Glasses

Beckert, Steffen; Gratz, Marcel; Kullmann, Jens; Enke, Dirk; Stallmach, Frank

doi:10.1007/s00723-013-0447-9

Cited by 7 publications

(4 citation statements)

References 31 publications

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“…[11][12][13][14] For instance, computer simulation studies observed only moderately reduced diffusivities of ions and water near interfaces. 15,16 Backscattering neutron spectroscopy 17 and nuclear magnetic resonance (NMR) 18,19 studies probed the integral dynamic behavior of electrolyte solutions in silica matrices and found that ion and water mobilities are moderately lower in confinements with sizes of a few nanometers than in the bulk. Consistent with these studies at room temperature, it was found in calorimetric measurements at cryogenic temperatures that the glass transition temperature Tg is only slightly higher in such narrow silica confinements.…”

Section: Introductionmentioning

confidence: 99%

“…26,27 Against this backdrop, it is intriguing to ascertain confinement effects for water-mimetic liquids, in particular, for LiCl solutions. While the aforementioned studies addressed this problem at high or low temperatures, [17][18][19][20] it is the goal of this contribution to investigate the dynamics of glass-forming LiCl solutions in silica pores of various diameters d throughout the whole supercooled temperature range, especially near the proposed second critical point of bulk water at ∼225 K.…”

Section: Introductionmentioning

confidence: 99%

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NMR studies on the influence of silica confinements on local and diffusive dynamics in LiCl aqueous solutions approaching their glass transitions

Schneider

Säckel

Brodrecht

et al. 2020

The Journal of Chemical Physics

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We use 1H, 2H, and 7Li NMR to investigate the molecular dynamics of glass-forming LiCl-7H2O and LiCl-7D2O solutions confined to MCM-41 or SBA-15 silica pores with diameters in the range of d = 2.8 nm–5.4 nm. Specifically, it is exploited that NMR experiments in homogeneous and gradient magnetic fields provide access to local and diffusive motions, respectively, and that the isotope selectivity of the method allows us to characterize the dynamics of the water molecules and the lithium ions separately. We find that the silica confinements cause a slowdown of the dynamics on all length scales, which is stronger at lower temperatures and in narrower pores and is more prominent for the lithium ions than the water molecules. However, we do not observe a temperature-dependent decoupling of short-range and long-range dynamics inside the pores. 7Li NMR correlation functions show bimodal decays when the pores are sufficiently wide (d > 3 nm) so that bulk-like ion dynamics in the pore centers can be distinguished from significantly retarded ion dynamics at the pore walls, possibly in a Stern layer. However, we do not find evidence for truly immobile fractions of water molecules or lithium ions and, hence, for the existence of a static Stern layer in any of the studied silica pores.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

NMR studies on the influence of silica confinements on local and diffusive dynamics in LiCl aqueous solutions approaching their glass transitions

Schneider

Säckel

Brodrecht

et al. 2020

The Journal of Chemical Physics

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“…This fact, in addition to the great biological, geological, and technological interest in geometrically confined water and aqueous solutions has caused a rapidly growing interest of such confined systems. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Issues of importance to explore are, for instance, how the hydrogen bonds in the corresponding bulk system are altered in different types of confined geometries, and how this, in turn, affects the glass transition related dynamics. In this paper we have used broadband dielectric spectroscopy and differential scanning calorimetry (DSC) to explore how the dynamical bulk behaviors of aqueous solutions of PG and PGME are altered by the intercalation in a two-dimensional vermiculite clay.…”

Section: Introductionmentioning

confidence: 99%

Glass transition and relaxation dynamics of propylene glycol–water solutions confined in clay

Elamin

Björklund

Nyhlén

et al. 2014

The Journal of Chemical Physics

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The molecular dynamics of aqueous solutions of propylene glycol (PG) and propylene glycol methylether (PGME) confined in a two-dimensional layer-structured Na-vermiculite clay has been studied by broadband dielectric spectroscopy and differential scanning calorimetry. As typical for liquids in confined geometries the intensity of the cooperative α-relaxation becomes considerably more suppressed than the more local β-like relaxation processes. In fact, at high water contents the calorimetric glass transition and related structural α-relaxation cannot even be observed, due to the confinement. Thus, the intensity of the viscosity related α-relaxation is dramatically reduced, but its time scale as well as the related glass transition temperature Tg are for both systems only weakly influenced by the confinement. In the case of the PGME-water solutions it is an important finding since in the corresponding bulk system a pronounced non-monotonic concentration dependence of the glass transition related dynamics has been observed due to the growth of hydrogen bonded relaxing entities of water bridging between PGME molecules [J. Sjöström, J. Mattsson, R. Bergman, and J. Swenson, Phys. Chem. B 115, 10013 (2011)]. The present results suggest that the same type of structural entities are formed in the quasi-two-dimensional space between the clay platelets. It is also observed that the main water relaxation cannot be distinguished from the β-relaxation of PG or PGME in the concentration range up to intermediate water contents. This suggests that these two processes are coupled and that the water molecules affect the time scale of the β-relaxation. However, this is most likely true also for the corresponding bulk solutions, which exhibit similar time scales of this combined relaxation process below Tg. Finally, it is found that at higher water contents the water relaxation does not merge with, or follow, the α-relaxation above Tg, but instead crosses the α-relaxation, indicating that the two relaxation processes are independent of each other. This can only occur if the two processes do not occur in the same parts of the confined solutions. Most likely the hydration shell of the interlayer Na(+) ions is causing this water relaxation, which does not participate in the α-relaxation at any temperature.

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“…Single phase II ASA crystals can be obtained by crystallization of aspirin in the presence of anhydrous ASA in organic solvents [11,12]. DSC measurements revealed the difference in melting phase transition temperature at 135.5°C for phase II and at 144.9°C for phase I [13].…”

Section: Introductionmentioning

confidence: 99%

Confinement-induced polymorphism in acetylsalicylic acid–nanoporous glass composites

et al. 2018

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We report on the experimental observation of confinement-induced new phase appearance in acetylsalicylic acid (ASA)-porous glass (PG) composites. In this study, ASA was embedded in PG host matrices of various pore widths (15-200 nm). The Raman spectra and positron annihilation lifetime measurements exhibit the existence of ASA nanocrystals in the PG matrix. The DSC data revealed that the melting temperature T M and excess specific heat decrease with decreasing the size of embedded ASA nanocrystals. The close inspection of the T M dependence versus diameter of filled pores has shown that the ASA crystallizes in polymorph II in confined matrix. Moreover, it was demonstrated that the ASA spatial confinement results in the appearance of new polymorphic phase in the investigated composites-highly likely form ASA III. Both the changes in ASA melting temperatures due to the volume constraints and the decrease in specific heat may be crucial for the bioavailability of the drug.

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Concentration-Dependent Self-Diffusion of Water in Aqueous Solutions of Lithium Chloride Confined to Porous Glasses

Cited by 7 publications

References 31 publications

NMR studies on the influence of silica confinements on local and diffusive dynamics in LiCl aqueous solutions approaching their glass transitions

NMR studies on the influence of silica confinements on local and diffusive dynamics in LiCl aqueous solutions approaching their glass transitions

Glass transition and relaxation dynamics of propylene glycol–water solutions confined in clay

Confinement-induced polymorphism in acetylsalicylic acid–nanoporous glass composites

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