Anomalously Immobilized Water: A New Water Phase Induced by Confinement in Nanotubes

Confinement can induce unusual behavior in the properties of matter. Using molecular dynamics simulations, we show here that water confined to carbon nanotubes of a critical size under ambient conditions (1 bar, 300 K) can undergo a transition into a state having icelike mobility with an amount of hydrogen bonding similar to that in liquid water. The onset of this behavior occurs rapidly, raising the possibility that confinement inside nanotubes, and perhaps even buckyballs, can provide an environment in which the dynamics of phase changes may be studied directly by simulation. Moreover, because of a variety of evidence suggesting that water ordering may modulate proton conductance via a "proton wire" hydrogen bonding network, the ability to modulate water ordering with geometry suggests a possible mechanism for a switchable nanoscale semiconductor.