The Meniscus Instability in Non-Newtonian Negative Squeeze Films

Abstract

This paper treats an instability at the free surface of non-Newtonian (power-law) fluid films between two tilted plates in a negative squeeze motion. The meniscus instability in a fluid with the power-law constitutive equation was analyzed on the basis of the linear stability theory. In the analysis, a capillary number for the power-law fluid was newly defined and the relationship between the capillary number and the criterion for the instability of meniscus was theoretically deduced. In the experiment, a water solution of polyacrylamide (separan) whose viscosity obeys a power-law of the strain rate was used as a sample fluid, the meniscus instability in the fluid was examined by using a VTR and the wavelength of disturbances was measured. The theoretical criterion for the instability was in good agreement with experiments and the capillary number could rearrange well the experimental results for the disturbances.