Deformation of a Newtonian drop in a viscoelastic matrix under steady shear flow. Experimental validation of slow flow theory

The small deformation of a single drop in a Boger fluid under steady-state slow shear flow is here investigated by video-enhanced microscopy and image analysis. Data are compared to predictions of a recent perturbation analysis, dealing with the drop-in-a-flow-field problem for viscoelastic fluid components [J. Non-Newt. Fluid Mech. 107 (2002) 111]. The main experimental result, in agreement with theory, is that drop orientation towards the flow direction is significantly enhanced as compared to the Newtonian case. In fact, based on this result, an optical determination of the first normal stress difference of the matrix fluid can be obtained. Furthermore, it is shown here that the interfacial tension of the fluid pair can be readily obtained by comparison between the theoretical predictions and the optical data taken in both the “side” and “top” views (i.e. along the vorticity and velocity gradient direction, respectively) of the deformed drop.