Transient Gel Collapse Captured on Film

We have captured the onset of collapse of a transient gel “on film”, in other words in a time series of 3D confocal image stacks. So far as we are aware this process has never before been captured in this way.

The emulsion system comprised 30% oil aggregated with 0.1% PEO. Each image stack in the time series comprised 64 slices, and measured 107.3 microns in x, y and 30.7 microns in the z direction, the direction of motion into the sample.

The animations below, commencing at times t= 700, 840, 980, 1277 and 2627 seconds after the start of the imaging run, each progress deeper into the sample a slice at a time. The direction of gravity is down: the sample is viewed sideways on. Bear in mind that since each stack in evolving so rapidly these movies are not true 3D + time. The image quality has been slightly degraded in the process of turning the stacks into animations.

Early on, at t=700 seconds, the aggregated emulsion is sedimenting slowly and uniformly downwards. Not much is happening. Time per slice = 2.1 seconds. Download movie clip [AVI, 3Mb]

At t=840 seconds the bulk movement is transverse to the direction of gravity, and changes direction part-way through the sequence. Aggregates retain their integrity. Some small localised motion hot-spots are plainly visible. Time per slice = 2.1 seconds. Download movie clip [AVI, 2.5Mb]

At t=980 seconds again the bulk movement is mainly transverse, though rather more tentative. Time per slice = 2.1 seconds. Download movie clip [AVI, 2Mb]

At t=1277 seconds, movement is dramatic and shows bulk swirls. The overall direction of motion is now vertical. This sequence shows a nice example of a “jolt” about half way through. Time per slice = 4 seconds. Download movie clip [AVI, 1.5Mb]

At t=2627 seconds the aggregates are moving vertically and uniformly at relatively high speed. Aggregates maintain their integrity, with little discernible relative movement between aggregates. Time per slice = 4 seconds. Download movie clip [AVI, 1Mb]

To summarise, in the early stages movement is slow and downward, turning to long-range swirls and finally to rapid upward motion. Aggregates are not seen to break up or coalesce, though in the final sequence visual inspection suggests that aggregates have become less ramified, more widely spaced and possibly oriented vertically. Large droplets remain part of aggregates.

In trying to understand this behaviour, it is worth remembering that the microscopy window is small and that simultaneous behaviour elsewhere in the sample could be quite different. Notice also that the time per image slice in the first three movies is half that of the final two.