Direct observation of the dynamics of single metal ions at the interface with solids in aqueous solutions.

ABSTRACT: The dynamics of ions adsorbed at the surface of immersed charged solids plays a central role in countless natural and industrial processes such as crystal growth, heterogeneous catalysis, electrochemistry, or biological function. Electrokinetic measurements typically distinguish between a so-called Stern layer of ions and water molecules directly adsorbed on to the solid's surface, and a diffuse layer of ions further away from the surface. Dynamics within the Stern layer remain poorly understood, largely owing to a lack of in-situ atomic-level insights. Here we follow the dynamics of single Rb+ and H3O+ ions at the surface of mica in water using high-resolution atomic force microscopy with 25?ms resolution. Our results suggest that single hydrated Rb+ions reside ?1?=?104?±?5?ms at a given location, but this is dependent on the hydration state of the surface which evolves on a slower timescale of ?2?=?610?±?30?ms depending on H3O+ adsorption. Increasing the liquid's temperature from 5?°C to 65?°C predictably decreases the apparent glassiness of the interfacial water, but no clear effect on the ions' dynamics was observed, indicating a diffusion-dominated process. These timescales are remarkably slow for individual monovalent ions and could have important implications for interfacial processes in electrolytes.

SUBMITTER: Ricci M 

PROVIDER: S-EPMC5322364 | biostudies-literature | 2017 Feb

REPOSITORIES: biostudies-literature