Abstract

In order to understand the molecular mechanics involved in the adhesion of a bimaterial interface bond, a Raman microprobe shear apparatus has been designed and fabricated. The apparatus is fabricated to perform a pure shear experiment on a bimaterial interface produced by the vapor deposition of a thin film of ice on a cold metallic substrate under a controlled temperature, humidity, and vapor-flow rate environment. The textures of four metal surfaces (titanium, copper, aluminum, stainless steel) and one polymer surface have been investigated with the use of the scanning electron micrograph. The shear experiment is optically coupled to a Raman microprobe at the 180° and 135° scattering geometry. The Raman spectra provide <i>in situ</i> information regarding the molecular structure and vibrational modes at the bimaterial interface before and after the shearing event. The results indicate that the adhesive bonds are formed primarily by the interaction of oxygen atoms in the ice lattice with the atoms of the solid surface. A solid, which displays good lattice matching with ice, shows good adhesive strength. The adhesive strength is found to be proportional to the extent of mechanical interlocking and inversely proportional to the contact angle of the water droplet. An activation energy analysis of the adhesive strength shows that the failure of the ice/metal bond is rate sensitive while the ice/polymer bond is relatively insensitive to the strain rate. The failure of the ice/metal bond is cohesive while the failure of the ice/polymer bond is interfacial. The structure of the ice layers on metals is polycrystalline, which is marginally influenced by the crystalline structure of the substrate and shows increased ordering in vibrational modes. The sheared ice has a larger number of defects as reflected by the increase in the half-power bandwidth of the Raman peaks.

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