Translational diffusion of water and its dependence on temperature in charged and uncharged clays: A neutron scattering study

Abstract

Structural changes of poly( N -isopropylacrylamide)-based microgels induced by hydrostatic pressure and temperature studied by small angle neutron scattering J. Chem. Phys. 133, 034901 (2010) The water diffusion in four different, highly compacted clays ͓montmorillonite in the Na-and Ca-forms, illite in the Na-and Ca-forms, kaolinite, and pyrophyllite ͑bulk dry density b = 1.85Ϯ 0.05 g / cm 3 ͔͒ was studied at the atomic level by means of quasielastic neutron scattering. The experiments were performed on two time-of-flight spectrometers and at three different energy resolutions ͓FOCUS at SINQ, PSI ͑3.65 and 5.75 Å͒, and TOFTOF at FRM II ͑10 Å͔͒ for reliable data analysis and at temperatures between 27 and 95°C. Two different jump diffusion models were used to describe the translational motion. Both models describe the data equally well and give the following ranking of diffusion coefficients: Na-montmorilloniteഛ Ca-montmorilloniteϽ Ca-illite Ͻ Na-illiteϽ waterഛ pyrophylliteഛ kaolinite. Uncharged clays had slightly larger diffusion coefficients than that of bulk water due to their hydrophobic surfaces. The time between jumps, t , follows the sequence: Ca-montmorilloniteജ Na-montmorilloniteϾ Ca-illiteϾ Na-illiteജ kaolinite Ͼ pyrophylliteജ water, in both jump diffusion models. For clays with a permanent layer charge ͑montmorillonite and illite͒ a reduction in the water content by a factor of 2 resulted in a decrease in the self-diffusion coefficients and an increase in the time between jumps as compared to the full saturation. The uncharged clay kaolinite exhibited no change in the water mobility between the two hydration states. The rotational relaxation time of water was affected by the charged clay surfaces, especially in the case of montmorillonite; the uncharged clays presented a waterlike behavior. The activation energies for translational diffusion were calculated from the Arrhenius law, which adequately describes the systems in the studied temperature range. Na-and Ca-montmorillonite ͑ϳ11-12 kJ/ mol͒, Na-illite ͑ϳ13 kJ/ mol͒, kaolinite and pyrophyllite ͑ϳ14 kJ/ mol͒, and Ca-illite ͑ϳ15 kJ/ mol͒ all had lower activation energies than bulk water ͑ϳ17 kJ/ mol in this study͒. This may originate from the reduced number and strength of the H-bonds between water and the clay surfaces, or ions, as compared to those in bulk water. Our comparative study suggests that the compensating cations in swelling clays have only a minor effect on the water diffusion rates at these high densities, whereas these cations influence the water motion in non-swelling clays.

Elucidation of Diffusivity of Hydrogen Isotopes in Flexible MOFs by Quasi‐Elastic Neutron Scattering

“…The Gaussian distribution describes the continuous diffusion reflected in elastic scattering signals, whereas the Lorentzian distribution explains the complex diffusion process with a diffusion time greater than the neutron experimental time scale. [ 24 ] The width of the Lorentzian distribution for deuterium is broader than that of hydrogen at 77 K, indicating that the diffusion of deuterium is faster than that of hydrogen in MIL‐53(Al), which is in line with the results obtained for other rigid quantum sieving materials. [ 17 ]…”

Role of interlayer porosity and particle organization in the diffusion of water in swelling clays

“…However, such a relationship remains to be investigated in the case of clay media made of swelling clay particles with two types of porosities (i.e., interlayer and interparticle) being accessible for the water. In such dual-porosity media with charged surfaces, water mobility in the interlayer space can be drastically reduced compared to that in the interparticle porosity, as revealed by molecular dynamic simulations (Titiloye and Skipper, 2001;Marry et al, 2002;Malikova et al, 2006;Michot et al, 2012 among others) and quasi-elastic neutron scattering studies (González Sánchez et al, 2008a;Bestel, 2014) performed on low charge swelling clays, e.g. montmorillonite.…”

Slow dynamics, hydration and heterogeneity in Laponite dispersions

“…18 Other studies into diffusion of water, the dependence on temperature, and hydration in clay systems were carried out through experiments and simulations. [19][20][21][22][23][24][25] Desai et al found that the included water is likely to cause the phases in the bentonite clays. 26 Thus our present study of the hydration of Laponite and its phase behavior is studied systematically with aging.…”