Chemistry Reference
In-Depth Information
Fig. 7.9
Bacterial rectification using asymmetric walls [
26
].
To p
A microfabricated chamber with
inlet and outlet ports at
top
and
bottom
.Arowof
V-shaped
walls divides the chamber into two
halves. A fluorescence image of bacteria in the chamber where there is a uniform distribution at
the start of the experiment (
left
) and the steady state after 80 min (
right
).
Bottom
(
left
) Schematic
drawing of the interaction of bacteria with the walls. Bacteria on the
left side
may (trace 1) or
may not (trace 2) get through the gap, depending on the angle of attack. On the
right
, all bacteria
colliding with the wall are diverted away from the gap.
Bottom
(right) Snapshots from a simulation
[
27
], mimicking the above experiment, with point particles that move ballistically along walls
to a concentration on the right side of the chamber. Recent simulations [
27
] with
ballistic point swimmers in the presence of the asymmetric walls, revealed a similar
rectification effect. Therefore, the key ingredients for the rectification seem to be
ballistic motion along the walls and an asymmetry of the walls to guide the motion,
both readily available in our system.
We created a 2-dimensional chamber similar to the one shown in Fig.
7.9
with
V-shaped barriers separating the chamber into to equal halves. We guide droplet
squirmers into this chamber with an equal distribution on both sides of the barriers
and observe their dynamics. As seen in the top panel of Fig.
7.10
, which is an overlay
of 20 images, each 1 second apart, the walls have a guiding effect on the droplets
just as that described above for the case of the bacteria. While the droplets from
the bottom half are guided through the gaps, the walls reflect the droplets hitting
them from the top. Indeed, the swimmers move ballistically along the channel walls,
resulting eventually in an average movement of a population of swimmers from the
bottom half of the chamber to the top. Since the droplet size is smaller than the side
