Motorized droplets thanks to feedback effects

Date:
October 19, 2021
Source:
Heinrich-Heine University Duesseldorf
Summary:
Physicists have examined a special system of colloidal particles
that they activated using laser light. The researchers discovered
that self- propelling droplets, which they have named 'droploids',
formed which contain the particles as an internal motor.



FULL STORY ==========================================================================
A team of physicists from Germany and Sweden working with first author
Jens Christian Grauer from Heinrich Heine University Du"sseldorf (HHU)
has examined a special system of colloidal particles that they activated
using laser light.

The researchers discovered that self-propelling droplets, which they
have named 'droploids', formed which contain the particles as an internal motor. They describe these droploids in more detail in the latest edition
of the journal Nature Communications.


========================================================================== According to an age-old saying, the whole is often more than the sum of
its parts. After all, a sandwich made of bread, lettuce and mayonnaise
tastes better than its individual components. A team of physicists from
HHU, TU Darmstadt and Sweden's University of Gothenburg has determined
that this adage is also true in the realm of physics, and that combining individual parts can create something with entirely new properties.

The research project involved combining different atoms and larger
particles and studying the effects they have on each other. It is
ultimately a typical example of what the matter that surrounds us
is composed of. The researchers extended this general principle of
combination to include additional feedback processes, thus creating new
kinds of dynamic structures referred to as 'positive feedback loops'.

Specifically, they combined two different types of colloid particles --
in a water-lutidine heat bath. They irradiated the bath with lasers,
and the light from the lasers brought the liquid near the particles to
the critical point.

The fluctuations are particularly strong at this point, allowing
droplet-like structures to form that in turn surround the particles.

Inside the droplets, the two types of colloid particles heat up to
different temperatures. This results in effective forces that contradict Newton's fundamental law of motion (actio = reactio) to propel the
droplets forwards.

This means that the colloid particles induce the formation of droplets
that encapsulate the colloids and are in turn propelled by the
particles. This feedback loop results in novel superstructures with
a self-organised colloidal motor. The researchers adopted the term
'droploids', a portmanteau of the words 'droplets' and 'colloids',
to describe these superstructures.

The research team combined theoretical and experimental approaches,
with the system modelling performed in Du"sseldorf and Darmstadt, while
the colleagues in Gothenburg verified the findings using real-life
experiments, thus confirming the theoretical models.

Prof. Dr. Hartmut Lo"wen, Head of the Institute of Theoretical Physics
II at HHU, had this to say: "It's important here that the process can
be controlled entirely by laser illumination. This makes it possible
to steer the system externally so that it is flexible for different applications." Prof. Dr. Benno Liebchen, leader of the "Theory of Soft
Matter" working group at TU Darmstadt, explained the actual use of the droploids as follows: "Besides justifying a novel concept for micromotors,
the droploids and the non- reciprocal interactions involved could serve
as important ingredients for generating future biomimetic materials." ========================================================================== Story Source: Materials provided by
Heinrich-Heine_University_Duesseldorf. Note: Content may be edited for
style and length.


========================================================================== Journal Reference:
1. Jens Grauer, Falko Schmidt, Jesu's Pineda, Benjamin Midtvedt,
Hartmut
Lo"wen, Giovanni Volpe, Benno Liebchen. Active droploids. Nature
Communications, 2021; 12 (1) DOI: 10.1038/S41467-021-26319-3 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211019110532.htm

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