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From the same paper as the previous image.
This figure presents a series of confocal fluorescence microscopy images of capsules, staining the wall by a dye, on increasing the outside polyelectrolyte (PE = PSS) concentration. One realizes that at low PSS concentration all the capsules are nicely spherical. However, at high PSS concentration they are all buckled. By quantitatively measuring the fraction of buckled capsules as a function of external PSS concentration, one can obtain a critical external osmotic pressure, π(crit), for which most of the capsules are buckled (See top frame in the next slide). Then, by varying the capsule wall thickness t for a given capsule radius R, one can obtain the square-dependence of π(crit) on t/R (bottom frame in the next slide), and from that dependence and the classical buckling formula for an externally pressurized spherical shell one can obtain the effective elastic modulus of the multilayered capsule wall.
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