Two accurate optical methods for Newtonian viscosity measurement, and observations on a surface effect with silicon oil

The paper shows how earlier work on the flow of oil films under gravity and centrifugal force may be adapted to give accurate absolute measurements of viscosity over a range from 5*10-5 m2 s-1 to 0.1 m2 s-1. In the gravity technique the oil flows down a steel plate. In the rotation technique it is placed on a small steel disc rotated at 50 rev s-1. In both techniques thickness measurement is by interferometry, timing and recording by minicomputer. Results show good agreement between the two methods, and standard deviations of nu are around 0.2%. The rotational method is shown to be more versatile and potentially more accurate, and prospects for future improvement are discussed. An advantage of the method is the very small volume of fluid, about 5 mm3, required. A surface effect is apparent with the silicon oils, affecting a thickness of the order of 40 nm, and a brief study of this is included.