In order to reduce the sheer forces on the vesicles, a relatively low flow rate of 2 mL/s was used, resulting in a dead time, t dead = 0.0078 s = 7.8 ms. The first frame is captured right before the end of the mixing phase and hence the first kinetic time is equal to the dead time. The wait time, t wait , between the fist and second frames is 5.0 ms, and increases according to a geometric progression with a common ratio of 1.2 between subsequent frames. The X-ray beam is blocked during the wait time by means of a fast beam shutter. Furthermore, the incident intensity was attenuated by a factor 10 in order to avoid any potential X-ray induced effects. The frame acquisition (exposure) time, t aqc , is 5.0 ms for all frames, and the kinetic time is taken to be at the midpoint of each frame. Hence, the time of frame i = 2, 3, ..., 50 (i.e. from the second frame onward) is given as t i = t dead + j<i (t wait,j + t aqc /2). A total of 50 frames are taken, the last one being at 189.7 s, and the kinetic times for all frames are given in SI (Table ). A final frame several minutes later was captured to confirm that the final state had been reached.