Biological membranes are dynamical entities that can rapidly adjust their composition and biophysical properties in response to external stimuli. This is partly achieved through a highly localised control of the molecular mobilities within the membrane, influenced by different lipid nanodomains, crowded protein regions, and contacts with cytoskeletal and external structures. The membrane is further coupled to the behaviour of the adjacent water and ions, rendering nanoscale quantitative measurements challenging.

Here we use approaches based on atomic force microscopy (AFM) to map to map the equilibrium organisation and local diffusion dynamics at membrane-water interfaces with nanoscale precision. The results, complemented by computer simulations, show an interplay between local effects and the emergence of mesoscale phenomena over hundreds of nanometres. For example, water-stabilised ionic clusters can spontaneously for over seconds and dramatically alter the biophysical properties of membranes with functional consequences. We also track the coupled mobility of interfacial water and of lipid molecules within fluid membranes, and show that correlated motion can control self-assembly.