Interactions and Transport of Charged Species in Bulk and at Interfaces
Heterogeneous dynamics of water in soft confinementSam Hanot
Institute Laue-Langevin, Grenoble, France, France
Coauthor(s) : Stefano Mossaa*, and Sandrine Lyonnarda
Univ. Grenoble Alpes, CEA-INAC, F-38000 Grenoble, France
Confinement at the nano-scale and interaction with interfaces profoundly alter structure and dynamics of water. Grasping the nature of these modifications at the molecular level is crucial, in contexts as diverse as biology or materials science. A situation of broad interest is that of water adsorbed in natural or synthesized soft media, including biomolecules, polymers, self-assembled or active materials. The function-structure interplay in these systems is expected to correlate to the peculiar properties of the adsorbed fluid. In particular, water close to soft charged boundaries shows significant deviations from the bulk state, which in turn profoundly impacts the morphology and functional response of the confining medium. Insight on this complex interplay can be obtained by computer simulation.
I will discuss our recent Molecular Dynamics simulation work on a self-assembling model system, to demonstrate and rationalize the existence of spatially heterogeneous dynamics in water adsorbed in soft confining media. We have followed the evolution of water confined in ionic surfactants phases, ranging from lamellae to micelles, at low and high hydration respectively. We have analysed in depth the main dynamical features, also in terms of quantities measured in scattering experiments with Neutrons, and found clear evidences of anomalous sub-diffusion. We have identified water molecules lying at the charged interfaces with the hydrophobic confining matrix as the main responsible for this unusual feature, and given a comprehensive picture for dynamics based on a precise analysis of life-times at the interfaces. I will conclude by proposing a unified picture for rationalizing the existence of dynamical heterogeneities in fluids under soft confinement.
 S. Hanot, S. Lyonnard, and S. Mossa, Soft Matter 11, 2469 (2015)
 S. Hanot, S. Lyonnard, and S. Mossa, Nanoscale 8, 3314 (2016)