Chemistry Reference
In-Depth Information
coarse grained such that microscopic details are ignored. Experimental work has
been mainly focussed on using shaken granular media and bacterial populations
[
4
,
19
]. The only interactions in granular media are those due to excluded volume
interactions and hydrodynamic interactions are fully absent. Experiments with bac-
terial populations are not only due to the particular importance of understanding the
collective behaviour of micro-organisms, but also because these are the only rela-
tively simple active swimmers which can be obtained in sufficient number. Even a
bacterium, however, is much more complex than the model elements used so far in
theories. Consequently, it is not yet clear which aspects of their collective behaviour
are due to physical interactions, and which trace down to more complex biological
signalling. The physical interactions are mainly mediated by the medium in which
the SPPs are suspended i.e. hydrodynamic interactions or are due to excluded volume
interactions. Biochemical interactions include olfactory, visual or chemotactic cues.
Not only flocking behaviour, but also in microbial settings, swimming can signif-
icantly affect the distribution of nutrients and chemical signals which are typically
thought to only diffuse due to their sizes. The strong flow fields of swimmers can
change the distribution of passive media via advection and this is of great significance
in understanding population dynamics and evolution. Further, it has been suggested
that the hydrodynamic interactions of swimming micro-organisms at interfaces may
have biological implications such as in fertizilation and reproduction [
20
].
In this chapter we investigate the various interactions of the droplet squirmers:
(i) with each other, (ii) with passive tracers, (iii) with walls and finally (iv) in one-
dimensional confinement.
7.2 Experimental Techniques
The experimental techniques used for the results in this chapter are the same as those
All the droplet squirmers here are produced using the non-oscillating B-Z mix-
ture which consists of two parts: (i) 50mM sulphuric acid (H
2
SO
4
) and 28mM
sodium bromate (NaBrO
3
) (ii) 400mM malonic acid (C
3
H
4
O
4
) and 2.7mM ferroin
(C
36
H
24
FeN
6
O
4
S). Droplets of this reaction mixture are produced in an external oil
phase of squalane containing 200mMmono-olein by PDMS microfluidic techniques
using step emulsification. The two dimensional observation areas are formed either
by two hydrophobic glass plates separated by PDMS spacer or are large areas on the
same PDMS chip that is used to produce the droplets. Quasi one dimensional exper-
iments are performed in hydrophobised glass capillaries (Hilgenberg GmbH) with
square cross sections of inner width of 100
m. Image
processing and droplet tracking is done using MATLAB, ImageJ and ImagePro-Plus
(Media Cybernetics) and the data is analysed using MATLAB.
μ
m and outer width of 135
μ
