  We report on experiments that consist in deforming a collection of
monodisperse droplets produced by a microfluidic chip through a flow-focusing
device. We show that a proper numerical modelling of the flow is necessary to
access the stress applied by the latter on the droplet along its trajectory
through the chip. This crucial step enables the full integration of the
differential equation governing the dynamical deformation, and consequently the
robust measurement of the interfacial tension by fitting the experiments with
the calculated deformation. Our study thus demonstrates the feasibility of
quantitative in-situ rheology in microfluidic flows involving e.g. droplets,
capsules or cells.
