Measuring the dihedral angle of water at a grain boundary in ice by an optical diffraction method

• Published in: Journal of Glaciology
• Main Authors: Walford, M.E.R., Nye, J.F.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1991
• Subjects: Earth-Surface Processes; Journal of Glaciology
• Online Access: http://dx.doi.org/10.1017/s0022143000042854; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143000042854

Abstract Optical measurements have been made on the water lenses which form under pressure at grain boundaries in polycrystalline ice. Monochromatic light from a point source is focused by the lenses but, because the lenses are microscopic in size, the image is blurred by diffraction. The diffraction pattern observed under a microscope has been compared with the computed diffraction pattern to deduce the angle 2 θ at the rim of each lens. This is the dihedral angle for water at a grain boundary in ice, and gives the ratio of the grain-boundary energy to that of an ice-water interface. The most sensitive measurements are those made on the rings of the virtual diffraction pattern formed on the object side of the lens. They give θ = 12.5 ± 0.5° for the grain boundary under observation, which is 26% lower than the previous value for θ found by ignoring diffraction.