Marino Simeone

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

Abstract 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.

Red blood cell deformation in microconfined flow

In this work, we report on a systematic fluidodynamic investigation of red blood cell (RBC) suspensions flowing in microcapillaries with diameters comparable to the cell size in vitro. By using high-speed video microscopy and image analysis, we provide the first simultaneous determination of both cell velocity and shape parameters related to RBC membrane deformability over an extended range of pressure drops, and the first quantitative comparison with theoretical results from the literature. Good agreement was found with the predicted axisymmetric shapes tending towards an apparent bullet-like asymptotic configuration at increasing cell velocity. A potential application of this work is in the design of flow-based devices to study the pathological conditions affecting cell deformability, thus allowing us to overcome the limits of classical static methods, such as micropipette aspiration, which are not suitable for handling a large number of cells.