Continuous Freezing and Melting of Water in Proximity to Nanostructured CuO Coatings¹

Nanostructured, hydrophilic CuO coatings have been used to enhance the performance of oscillating heat pipes. We use neutron scattering techniques to elucidate the effect of these coatings on the microscopic structure and dynamics of interfacial fluid (water). Our incoherent elastic neutron scattering and neutron diffraction measurements have shown that CuO interfacial water freezes continuously over the range 280 K to 200 K consistent with the formation of amorphous ice. To investigate the dynamics of water interacting with these CuO surfaces on a ns to ps time scale, we are using two backscattering spectrometers [HFBS at the NIST Center for Neutron Research and BASIS at the Oak Ridge Spallation Neutron Source (SNS)] and the cold neutron chopper spectrometer CNCS at the SNS. Preliminary measurements on the CNCS indicate that at 293 K the dominant contribution to the quasielastic spectra is from the diffusion of bulk-like water. However, spectra at 250 K taken on the HFBS from a sample of comparable hydration show water diffusing about 4 times slower than bulk supercooled water at this temperature. We expect our measurements on BASIS to yield a detailed temperature dependence of the diffusion rate of the interfacial water.