Premelting at ice-solid interfaces studied via velocity-dependent indentation with force microscope tips

Abstract

We have indented the surface of ice at temperatures between Ϫ1°C and Ϫ17°C with sharp atomic force microscope tips. For a thick viscous interfacial melt layer, a Newtonian treatment of the flow of quasiliquid between the tip and the ice suggests that indentations at different indentation velocities should have the same force/velocity ratio for a given pit depth. This is observed for silicon tips with and without a hydrophobic coating at temperatures between Ϫ1°C and Ϫ10°C implying the presence of a liquid-like layer at the interface between tip and ice. At temperatures below about Ϫ10°C the dependence of force on velocity is weaker, suggesting that plastic flow of the ice dominates. A simple model for viscous flow that incorporates the approximate shape of our tip is used to obtain an estimate of the layer thickness, assuming the layer has the viscosity of supercooled water. The largest layer thicknesses inferred from this model are too thin to be described by continuum mechanics, but the model fits the data well. This suggests that the viscosity of the confined quasiliquid is much greater than that of bulk supercooled water. The hydrophobically coated tip has a significantly thinner layer than the uncoated tip, but the dependence of thickness on temperature is similar. The estimated viscous layer thickness increases with increasing temperature as expected for a quasiliquid premelt layer.

The Quasi-Liquid Layer of ice revisited: the role of temperature gradients and tip chemistry in AFM studies

“…Regarding the QLL at the ice-air interface, the authors question the ability of AFM experiments to properly measure this thickness, as will be discussed in more detail in the Results section. Recent Molecular Dynamics simulations by Gelman Constantin et al (Gelman Constantin et al, 2015a) show that hydrophobic tips promote the presence of a QLL at the tip-ice interface during indentation, supporting the analysis performed by Pittenger et al (Pittenger et al, 2001). The authors do not find an effect of the tip on the thickness of the QLL 25 on the ice-air interface.…”

“…Among the experimental techniques, the smaller QLL thicknesses correspond to measurements such as Brewster reflectometry (Elbaum et al, 1993), XPS (Bluhm et al, 2002), X-ray scattering (Lied et al, 1994;Dosch et al, 1995 and and IR spectroscopy techniques Ewing, 2002 and2003). On the contrary, ellipsometry (Beaglehole and Nason, 1980;Furukawa et al, 1987) and AFM determinations (Petrenko, 1997;Bluhm and Salmeron, 1999;Döppenschmidt and Butt, 2000;Bluhm et al, 2000;Pittenger et al, 2001) give thicker QLL values. AFM experiments, for 30 instance, involve the interaction of a tip with the sample; thus, it is uncertain whether other phenomena are also involved in the measurements.…”

“…15 Measurements of the ice QLL layer thickness were reported in the literature using different experimental techniques such as Brewster reflectometry (Elbaum et al, 1993), ellipsometry (Beaglehole and Nason, 1980;Furukawa et al, 1987), X-Ray scattering (Lied et al, 1994;Dosch et al, 1995 and, proton channeling (Golecki and Jaccard, 1977), nuclear magnetic resonance (NMR) (Ishizaki et al, 1996), infrared spectroscopy Ewing, 2002 and2003;Richardson, 2006), photoelectron spectroscopy (XPS) (Bluhm et al, 2002), and atomic force microscopy (AFM) (Petrenko, 1997;Bluhm and 20 Salmeron, 1999;Bluhm et al, 2000;Döppenschmidt and Butt, 2000;Pittenger et al, 2001). …”

“…Pittenger et al (Pittenger et al, 2001) analyzed the force curves between the tip and the ice for different indentation/penetration rates. The ratio between force and indentation rate was studied using silicon tips, with and without hydrophobic coating, and evidence of the presence of a QLL between the tip and the ice was found between -1 and -10 ºC, 15 based on the observation that the mentioned ratio is constant for a given pit depth.…”

“…Some of the QLL thickness determinations using AFM were performed by analyzing force curves (Petrenko, 1997;Döppenschmidt and Butt, 2000;Pittenger et al, 2001); that is, measuring the force experienced by the AFM tip as it Atmos. Chem.…”