B. Pittenger et al., Premelting at ice-solid interfaces studied via velocity-dependent indentation with force microscope tips - art. no 134102, PHYS REV B, 6313(13), 2001, pp. 4102
We have indented the surface of ice at temperatures between -1 degreesC and
- 17 degreesC with sharp atomic force microscope tips. For a thick viscous
interfacial melt layer, a Newtonian treatment of the flow of quasiliquid b
t tween the tip and the ice suggests that indentations at different indenta
tion velocities should have the same force/velocity ratio for a given pit d
epth. This is observed for silicon tips with and without a hydrophobic coat
ing at temperatures between -1 degreesC and -10 degreesC implying the prese
nce of a liquid-like layer at the interface between tip and ice. At tempera
tures below about -10 degreesC the dependence of force on velocity is weake
r, suggesting that plastic flow of the ice dominates. A simple model for vi
scous flow that incorporates the approximate shape of our tip is used to ob
tain an estimate of the layer thickness, assuming the layer has the viscosi
ty of supercooled water. The largest layer thicknesses inferred from this m
odel are too thin to be described by continuum mechanics, but the model fit
s the data well. This suggests that the viscosity of the confined quasiliqu
id is much greater than that of bulk supercooled water. The hydrophobically
coated tip has a significantly thinner layer than the uncoated tip, but th
e dependence of thickness on temperature is similar. The estimated viscous
layer thickness increases with increasing temperature as expected for a qua
siliquid premelt layer.