ICE SOLID ADHESION ANALYSIS USING LOW-TEMPERATURE RAMAN MICROPROBE SHEAR APPARATUS

In order to understand the molecular mechanics involved in the adhesio n of a bimaterial interface bond, a Raman microprobe shear apparatus h as been designed and fabricated. The apparatus is fabricated to perfor m a pure shear experiment on a bimaterial interface produced by the va por deposition of a thin film of ice on a cold metallic substrate unde r a controlled temperature, humidity, and vapor-flow rate environment. The textures of four metal surfaces (titanium, copper, aluminum, stai nless steel) and one polymer surface have been investigated with the u se of the scanning electron micrograph. The shear experiment is optica lly coupled to a Raman microprobe at the 180-degrees and 135-degrees s cattering geometry. The Raman spectra provide in situ information rega rding the molecular structure and vibrational modes at the bimaterial interface before and after the shearing event. The results indicate th at the adhesive bonds are formed primarily by the interaction of oxyge n atoms in the ice lattice with the atoms of the solid surface. A soli d, which displays good lattice matching with ice, shows good adhesive strength. The adhesive strength is found to be proportional to the ext ent of mechanical interlocking and inversely proportional to the conta ct angle of the water droplet. An activation energy analysis of the ad hesive strength shows that the failure of the ice/metal bond is rate s ensitive while the ice/polymer bond is relatively insensitive to the s train rate. The failure of the ice/metal bond is cohesive while the fa ilure of the ice/polymer bond is interfacial. The structure of the ice layers on metals is polycrystalline, which is marginally influenced b y the crystalline structure of the substrate and shows increased order ing in vibrational modes. The sheared ice has a larger number of defec ts as reflected by the increase in the half-power band-width of the Ra man peaks.