title: Thermal conductance of hydrophilic and hydrophobic interfaces.
abstract: Using time-domain thermoreflectance, we have measured the transport of thermally excited vibrational energy across planar interfaces between water and solids that have been chemically functionalized with a self-assembled monolayer (SAM). The Kapitza length--i.e., the thermal conductivity of water divided by the thermal conductance per unit area of the interface--is analogous to the "slip length" for water flowing tangentially past a solid surface. We find that the Kapitza length at hydrophobic interfaces (10-12 nm) is a factor of 2-3 larger than the Kapitza length at hydrophilic interfaces (3-6 nm). If a vapor layer is present at the hydrophobic interface, and this vapor layer has a thermal conductivity that is comparable to bulk water vapor, then our experimental results constrain the thickness of the vapor layer to be less than 0.25 nm.
authors.affiliation: Department of Materials Science and Engineering, the Frederick Seitz Materials Research Laboratory, and the Beckman Institute for Advanced Science and Technology, University of Illinois, Urbana, Illinois 61801, USA.
authors.forename: Zhenbin
authors.initials: Z
authors.lastname: Ge
authors.forename: David G
authors.initials: DG
authors.lastname: Cahill
authors.forename: Paul V
authors.initials: PV
authors.lastname: Braun