Assessing Diffusion Relaxation of Interlayer Water in Clay Minerals Using a Minimalist Three-Parameter Model

Abstract

Using a minimal model approach for interpreting the intermediate scattering function, F(Q, t), to analyze quasi-elastic neutron scattering (QENS) data from interlayer water as a function of temperature in the 2D-layered clay minerals montmorillonite (Mt) and hectorite (Ht) a clear difference in behavior was observed. This was related to the polarization effect induced on the water molecules by both the exchangeable cation and surface charge within the interlayer. Although crucial for improving the wide range of industrial applications of clays as well as for explaining water uptake and retention by clays such information is neither obtained straightforwardly by other experimental methods nor fully accounted by molecular dynamics simulations. Furthermore, analysis of the evolution of the fitted parameters as a function of temperature shows that hydrogen atoms have a relaxation with a smaller average motional amplitude for Mt. Physically this can be explained as stronger hydrogen-bonding by water at the interlayer surfaces in Mt. These results allow for a novel and realistic description of these nanomaterials at the atomic scale, which is crucial for improving functional properties. These findings also prove that this new approach to modeling QENS captures subtle changes hidden in the spectra.

Uncovering the Dynamics of Confined Water Using Neutron Scattering: Perspectives

“…More specifically, QENS data gives insight in particularly crowded environments in the nanometer-nanosecond window, and biological applications are particularly important in this context [4,5,16,40,41]. To exploit QENS' full potential and allowing for instance to link QENS studies of protein dynamics with spectroscopic or kinetic experiments on biologically relevant time scales, such as dielectric and fluorescence correlation spectroscopy [66], harvesting information contained in QENS spectra needs a radical change in paradigm [12,15,16,26]. We consider that theoretical and molecular dynamics modelling, and consequently development of new models that provide direct insight into physical properties of bio-materials and -molecules, must be rigorously developed and implemented in the analysis of the experimental data.…”

“…Implementation of quantum interpretation of QENS describing the emergent properties of complex systems are urgently needed for a better description of the physical and chemical processes involved in complex systems. Development of "minimalistic" models to explain multiscale relaxation and anomalous diffusion, accounting for the non-Markovian properties of the dynamical heterogeneity of the water molecules constrained in a hydration environment is a promising idea [12,15,16,26]. The concept is to capture the form of QENS spectra with very few parameters and to relate these parameters to the form of the multi-minima "energy landscape" which is explored by the scattering atoms [12].…”

“…In complex systems, such as water dynamics in a constrained local environment, however, one is faced with an incompletely described problem, needing probabilistic methods to choose between likely models. An alternative, and very promising, approach is to compute the QENS spectrum theoretical parameters to identify physical models to analyze QENS data [14,15,26], and thus provide the needed experimental verification by using an energy landscape-based method [12,27]. In this new framework the QENS spectrum is described by its form, and the parameters related to the structure of the energy landscape; a concept in which the (free) energy of the system is represented by a convex envelope with many local minima and a distribution of barrier heights localized in a restricted domain of phase space.…”

“…In this Perspective article, we briefly describe why and how the MIRACLES time-of-flight backscattering spectrometer [19,28] being built at the European Spallation Source in Lund [18] will increase our understanding of water dynamics in complex systems. We will also discuss on how the vast scientific value of these data can be better exploited by using a new methodology in which the QENS spectrum theoretical parameters are computed and used to identify physical models to analyze QENS data [15,16,26] In this short Perspective, we do not attempt to lengthily review the field of QENS (and neutrons in general), we refer the interested reader to a very stimulating book where a general introduction into the production and properties of neutrons is followed by a series of papers describing the neutron scattering techniques used to study biological and biologically relevant systems [29].…”

Water Dynamics in Cancer Cells: Lessons from Quasielastic Neutron Scattering

“…In addition, the EISF has been recently explored as a minimalist approach for interpreting the intermediate scattering function, I ( Q , t ). With this method, the QENS data are parameterized in terms of the EISF, a relaxation time scale, and the relaxation form, τ ( Q ) and α ( Q ), and subtle changes hidden in the spectra can be captured [ 39 ].…”