  The mechanical properties of nanoconfined water layers are still poorly
understood and continue to create considerable controversy, despite their
importance for biology and nanotechnology. Here, we report on dynamic
nanomechanical measurements of water films compressed down to a few single
molecular layers. We show that the mechanical properties of nanoconfined water
layers change dramatically with their dynamic state. In particular, we observed
a sharp transition from viscous to elastic response even at extremely slow
compression rates, indicating that mechanical relaxation times increase
dramatically once water is compressed to less than 3-4 molecular layers.
