We investigate proton-charge mobility in nanoscopic water droplets with tuneable size. We find that the diffusion of confined proton charges causes a dielectric relaxation process with a maximumloss frequency determined by the diffusion constant. In volumes less than similar to 5 nm in diameter, proton-charge diffusion slows down significantly with decreasing size: for diameters < 1 nm, the diffusion constant is about 100 times smaller than in bulk water. The low mobility probably results from the more rigid hydrogen-bond network of nanoconfined water, since proton-charge mobility in water relies on collective hydrogen-bond rearrangements.

J. Chem. Phys.
Ultrafast Spectroscopy

van der Loop, T., Ottosson, N., Vad, T., Sager, W., Bakker, H., & Woutersen, S. (2017). Communication: Slow proton-charge diffusion in nanoconfined water. J. Chem. Phys., 146(13, Article number: 131101), 1–5. doi:10.1063/1.4979714