Chemistry Reference
In-Depth Information
many of the cellular structures and processes. Light microscopy, limited by the dif-
fraction barrier, is however restricted in the amount of structural information one
can extract about nanoscopic structures. While there have been advances in breaking
the diffraction barrier of light microscopy [
22
], it is not suitable in all situations. In
tially prove useful in imaging nanoscopic structures and particularly, in extracting
the structural information of lipid bilayers and transport processes such as those
described above.
1.2 Active Matter
The second part is about active matter and collective interactions that can occur in
nonequilibrium systems. In particular, we use active emulsions as a model active
matter system. The term active matter [
23
,
24
] refers to dynamic open systems that
constantly alter their state and are able to generate morphological changes, motion
and other complex behaviour. An emulsion is a mixture of two or more immiscible
liquids such that under appropriate conditions droplets of one liquid can be formed
in an external phase of the other. We use microfluidic water-in-oil emulsion droplets
with suitable chemical reactions running in the aqueous phase to create chemical
micro-oscillators and artificial swimmers. The emulsions are thus rendered active
due to the dissipation of chemical energy.
Spontaneous oscillations and motion represent the simplest examples of com-
plex dynamics and hence are ideally suited for a theoretical analysis of the inter-
actions and dynamic properties of a complex active system. Active oscillators can
generate spontaneous oscillations, which continue indefinitely. Spontaneous oscil-
lations occur only in nonlinear dynamic systems that are open i.e. there is a contin-
uous flow of energy through the system from its environment. Among the various
types of oscillatory systems such as mechanical pendula, cardiac and neural cells
or superconducting Josephson junctions to name just a few, a broad class of them
such as chemical and biological oscillators can be categorised as so called reaction-
diffusion systems. Systems such as those undergoing catalytic reactions at interfaces,
the Belousov Zhabotinsky reaction and social amoeba under stress display spatio-
temporal oscillatory patterns such as those shown in Fig.
1.4
which can be described
by a reaction-diffusion diffusion mechanism such as
2
u
∂
t
u
=
D
u
∇
+
f
(
u
,
v
,
k
1
),
2
v
τ∂
t
v
=
D
v
∇
+
g
(
u
,
v
,
k
2
)
(1.1)
which describes the evolution of the macroscopic variables, such as the concentra-
tions
u
and
v
, undergoing reaction,
f
and
g
with reaction constants
k
1
and
k
2
, and
diffusion with diffusivities
D
u
and
D
v
respectively. In the resulting spatio-temporal
patterns, the diffusion coefficients
D
i
(
i
=
u
,
v
) set the spatial scales while the rate
