The role of confined water in the emergence of electrostatic strong coupling as revealed by nanoseparated charged lipid layers

Swen Helstroffer; Ludovic Gardré; Giovanna Fragneto; Arnaud Hemmerle; Léo Henry; Laurent Joly; Fabrice Thalmann; Claire Loison; Pierre Muller; Thierry Charitat

doi:10.1021/acs.jpclett.5c01538

arXiv · 2505.11617

The role of confined water in the emergence of electrostatic strong coupling as revealed by nanoseparated charged lipid layers

Swen Helstroffer·Ludovic Gardré·Giovanna Fragneto·Arnaud Hemmerle·Léo Henry·Laurent Joly·Fabrice Thalmann·Claire Loison·Pierre Muller·Thierry Charitat

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Abstract

This study investigates the interplay between Strong Coupling (SC) attraction and hydration repulsion in nanoconfined water between like-charged phospholipid layers. It challenges the assumption that SC attraction requires multivalent counterions by showing that hydration water can enhance electrostatic interactions. We combine reflectivities with numerical simulations to analyze supported phospholipid layers under different relative humidity and surface charge densities. X-ray fluorescence demonstrates that we can control the valence of the associated counterions. Experimental measurement of the water thickness, combined with precise determination of charged surface positions by numerical simulations, enable us to compare our experiments with a theoretical model. It shows that charge-screening by hydration water induces SC attraction, even at moderate surface charge densities with monovalent counterions. Furthermore, hydration repulsion is stronger for DPPS compared to DPPC. These findings offer insights into the forces that control interactions between phospholipid layers and have important implications for biological and colloidal systems.

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Swen Helstroffer, Ludovic Gardré, Giovanna Fragneto, Arnaud Hemmerle, Léo Henry, Laurent Joly, Fabrice Thalmann, Claire Loison, Pierre Muller, Thierry Charitat. 2025-08-14. The role of confined water in the emergence of electrostatic strong coupling as revealed by nanoseparated charged lipid layers. https://doi.org/10.1021/acs.jpclett.5c01538

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