Article
Diverging Effects of NaCl and CsCl on the Mechanical Properties of Nanoconfined Water
Journal of the Electrochemical Society
(2018)
Abstract
Using an ultra-sensitive home-built atomic force microscope, we have studied the dynamic mechanical responses of pure water, 1 M NaCl, and 1 M CsCl aqueous solutions to understand the effects of ions on the viscoelastic properties of nanoconfined (≤ 1 nm) water films. In 1 M NaCl, we observed peaks in the Maxwell relaxation time, indicating a solid-like, elastic response due to jamming (dynamic solidification) during squeeze-out. NaCl also extended the range of ordering of water molecules further away from the mica surface up to 4–5 molecular layers (∼1 nm). By contrast, in 1 M CsCl, the relaxation time peaks were suppressed, even at high compression speeds, indicating a more liquid-like, viscous response. The addition of NaCl significantly increases the probability of the nanoconfined water film to react elastically in response to compression, while 1 M CsCl decreases the probability of water layers to show an elastic response. Our measurements support the notion that Na+ acts as a kosmotrope (order enhancer) and Cs+ as a chaotrope (order destroyer), directly influencing the hydration structure of water, and altering the mechanical response of the nanoconfined liquid layers to compression and squeeze-out.
Disciplines
Publication Date
2018
Citation Information
Peter M. Hoffmann and Shah H. Khan. "Diverging Effects of NaCl and CsCl on the Mechanical Properties of Nanoconfined Water" Journal of the Electrochemical Society (2018) Available at: http://works.bepress.com/peter_m_hoffmann/8/