Direct measurement of molecular stiffness and damping in confined water layers

Steve Jeffery*, Peter M. Hoffmann, John B. Pethica, Chandra Ramanujan, H. Özgür Özer, Ahmet Oral

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

101 Citations (Scopus)


We present direct and linear measurements of the normal stiffness and damping of a confined, few molecule thick water layer. The measurements were obtained by use of a small amplitude (0.36 Å), off-resonance atomic force microscopy technique. We measured stiffness and damping oscillations revealing up to seven molecular layers separated by 2.526 ± 0.482 Å. Relaxation times could also be calculated and were found to indicate a significant slow-down of the dynamics of the system as the confining separation was reduced. We found that the dynamics of the system is determined not only by the interfacial pressure, but more significantly by solvation effects which depend on the exact separation of tip and surface. The dynamic forces reflect the layering of the water molecules close to the mica surface and are enhanced when the tip-surface spacing is equivalent to an integer multiple of the size of the water molecules. We were able to model these results by starting from the simple assumption that the relaxation time depends linearly on the film stiffness.

Original languageEnglish
Article number054114
Pages (from-to)054114-1-054114-8
JournalPhysical Review B - Condensed Matter and Materials Physics
Issue number5
Publication statusPublished - Aug 2004
Externally publishedYes


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