  Encapsulation of chemicals using polymer membranes enables to control their
transport and delivery for applications such as agrochemistry or detergency. To
rationalize the design of polymer capsules, it is necessary to understand how
the membranes' mechanical properties control the transport and release of the
cargo. In this article, we use microfluidics to produce model polymer capsules
and study in situ their behavior in controlled elongational flows. Our model
capsules are obtained by assembling polymer mono and hydrogen-bonded bilayers
at the surface of an oil droplet in water. We also use microfluidics to probe
in situ the mechanical properties of the membranes in a controlled elongational
flow generated by introducing the capsules through a constriction and then in a
larger chamber. The deformation and relaxation of the capsules depend on their
composition and especially on the molecular interactions between the polymer
chains that form the membranes and the anchoring energy of the first layer. We
develop a model and perform numerical simulations to extract the main
interfacial properties of the capsules from the measurement of their
deformations in the microchannels.
