Drop shape under slow steady shear flow and during relaxation. Experimental results and comparison with theory

The three-dimensional small deformation of a single Newtonian drop immersed in an immiscible Newtonian liquid was investigated, both in slow steady shear and during retraction after cessation of shear. The experiments were performed in a parallel plate apparatus equipped with video-enhanced microscopy. The drop was observed from two perpendicular directions, and accurate measurements were obtained in each view by image analysis. The results were compared to existing theoretical predictions from the exact fluid dynamic problem, obtained perturbatively for the case of small deformations of the drop. Excellent agreement between data and theory was found, thus providing the first assessment of drop shape predictions in steady flow and relaxation for Newtonian fluids.