The liquid crystal of the bacteriophages showed dynamic chaos of active substance

Scientists first captured in real-time chaotic motion inside three-dimensional active
a liquid crystal. Earlier this behavior was primarily studied
by means of simulations and theoretical estimations. The obtained system can be
experimental platform for studying many phenomena in active media,
such as multicomponent fluids, metamaterials, biological tissues, and groups of robots or organisms, write the authors in the journal Science.

The substance is called active,
if it contains a large number of elements, capable of moving or
to develop mechanical force. Since this activity must be constantly
waste energy, such systems by definition can’t be in
the state of thermodynamic equilibrium. An alternative definition of active
of matter says that it should in response to the inflow of energy from outside to form
large ordered areas arising from local interactions
elements.

The active substance
meet both in animate and inanimate nature, and at various
scale. For example, such a system can be self-organizing biopolymers,
a flock of birds or dissolved in a fluid of self-propelled particles. Similar environment
some aspects can be similar to gases or liquids, but on the other
hand, they may experience a number of phenomena, not typical for passive physical
objects. Until recently, most artificial active media, with whom it was possible to experiment in the laboratory was two-dimensional.

Scientists from Germany, the Netherlands and the United States under the leadership of Guillaume
Duclos (Duclos Guillaume) from Brandeis University have combined a number of techniques and had the opportunity
watch in real-time for chaotic dynamics inside three-dimensional
liquid crystal (LCD). The authors used a nematic LC (elongated particles with
allocated average orientation), with the added cross bows,
which could be extended by external forces. As a result, the substance
there were mechanical stress and instability, which gave rise to flows on
the whole volume.

Nematic unable
to resist shear deformations and behave like liquid in this
case. However, if bent they exhibit the properties of elastic bodies and
resisting this effect. In active nematics small bending
deformation multiplied due to the properties of the environment that generates
volatility and volume flows, which are called active
turbulence. Unlike standard turbulence in ordinary fluids, such
the mode of chaotic currents is characterized by the predominant occurrence of vortices
of a certain size.

Active turbulence in
the nematic studied in detail in the two-dimensional case. In such thin films vortices
formed around topological defects in the orientation of liquid crystal molecules and behave
like electrical charges can attract or repel depending on
from mark. Such “topological charges” are constant, then
there are initially devoid of defects of the LCD can not be the total charge, and
no deformation cannot change their sign. As a result of external impact
lead to the emergence of pairs of vortices with opposite direction of rotation.

In contrast to the two-dimensional
case in three-dimensional nematics may experience fundamentally different types
defects — disclinations. They can take the form of lines or loops, and not
characterized by the charge, so can occur and disappear on their own. They
well-known in the static case, the negative environments but not actually observed
directly in active media in the dynamics so far.

As constituting a
particles of the crystals is elongated molecules, the authors used viral particles
bacteriophages, whose shape is also elongated and large compared to molecules
the size of the order of micrometers, it is easy to study. Bacteriophages form a nematic
at room temperature, and to make it the active medium, the authors joined
thereto the jumpers from the microtubules and molecular motors, dedicated to their
eukaryotic cells. Adding adenosine triphosphate — standard
intracellular energy carrier — molecular motors on the move, inside
nematic appeared mechanical stresses and any dimensional vortices.

Observations enough
high resolution both in time and in space managed to hold
using the technique of polarizing microscopy light sheet. This method
lies in the layering irradiation of the sample flat beam of light with high
speed. As a result, scientists were able to capture the emergence and evolution of vortices
in real-time.

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