Versatile, high-speed, and efficient crystal actuation with
photothermally resonated natural vibrations

Date:
April 20, 2023
Source:
Waseda University
Summary:
Mechanically responsive molecular crystals are extremely
useful in soft robotics, which requires a versatile actuation
technology. Crystals driven by the photothermal effect are
particularly promising for achieving high-speed actuation. However,
the response (bending) observed in these crystals is usually
small. Now, scientists address this issue by inducing large
resonated natural vibrations in anisole crystals with UV light
illumination at the natural vibration frequency of the crystal.


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FULL STORY ========================================================================== Mechanically responsive molecular crystals are extremely useful in
soft robotics, which requires a versatile actuation technology. Crystals
driven by the photothermal effect are particularly promising for achieving high-speed actuation. However, the response (bending) observed in these crystals is usually small. Now, scientists from Japan address this issue
by inducing large resonated natural vibrations in anisole crystals with
UV light illumination at the natural vibration frequency of the crystal.


========================================================================== Every material possesses a unique natural vibration frequency such that
when an external periodic force is applied to this material close to
this frequency, the vibrations are greatly amplified. In the parlance
of physics, this phenomenon is known as "resonance." Resonance is
ubiquitous in our daily life, and, depending on the context, could be
deemed desirable or undesirable. For instance, musical instruments like
the guitar relies on resonance for sound amplification. On the other hand, buildings and bridges are more likely to collapse under an earthquake
if the ground vibration frequency matches their natural frequency.

Interestingly, natural vibration has not received much attention in
material actuation, which relies on the action of mechanically responsive crystals.

Versatile actuation technologies are highly desirable in the field
of soft robotics. Although crystal actuation based on processes like photoisomerisation and phase transitions have been widely studied,
these processes lack versatility since they require specific crystals
to work. One way to improve versatility is by employing photothermal
crystals, which show bending due to light-induced heating. While promising
for achieving high-speed actuation, the bending angle is usually small (<0.5DEG), making the actuation inefficient.

Now, a team of scientists from Waseda University and Tokyo Institute of Technology in Japan has managed to overcome this drawback with nothing
more than the age-old phenomenon of resonated natural vibration. The
team, led by Dr. Hideko Koshima from Waseda University in Japan, used 2,4-dinitroanisole b- phase crystals (1b) to demonstrate large-angle photothermally resonated high- speed bending induced by pulsed UV
irradiation. Their research was published in Volume 14 of Nature
Communications and made available online on March 13, 2023.

"Initially, the goal of this research was to create crystals that
bend largely due to the photothermal effect. Therefore, we chose 2,4-dinitroanisole (1) b- phase crystal (1b), which has a large thermal expansion coefficient," explains Koshima, speaking of the team's
motivation behind the study. "We serendipitously discovered fast and
small natural vibration induced by the photothermal effect. Furthermore,
we achieved high-speed and large bending by photothermally resonating the natural vibration." In their work, the team first cooled a methanol
solution of commercially available anisole 1 to obtain hexagonal,
rod-shaped 1b single crystals. To irradiate them with UV light, they used
a pulsed UV laser with a wavelength of 375 nm and observed the bending
response of the crystal using a digital high- speed microscope. They
found that the rod-shaped 1b crystals showed, under UV irradiation,
a fast natural vibration at 390 Hz with a large photothermal bending of
nearly 1DEG, which is larger than the value of 0.2DEG previously reported
in other crystals. Further, the bending angle due to the natural vibraton increased to nearly 4DEG when irradiated with pulsed UV light at 390 Hz
(same as the crystal's natural frequency). In addition to this large
bending, the team observed a high response frequency of 700 Hz along
with the highest energy conversion efficiency recorded till date.

These findings were further confirmed through simulations performed
by the team. To their excitement, the simulation results showed
excellent agreement with experimental data. "Our findings show that
any light-absorbing crystal can exhibit high-speed, versatile actuation
through resonated natural vibrations.

This can open doors to the applications of photothermal crystals,
leading eventually to real-life soft robots with high-speed actuation capability and perhaps a society with humans and robots living in
harmony," concludes Koshima.

* RELATED_TOPICS
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========================================================================== Story Source: Materials provided by Waseda_University. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Yuki Hagiwara, Shodai Hasebe, Hiroki Fujisawa, Junko Morikawa, Toru
Asahi, Hideko Koshima. Photothermally induced natural vibration
for versatile and high-speed actuation of crystals. Nature
Communications, 2023; 14 (1) DOI: 10.1038/s41467-023-37086-8 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/04/230420110146.htm

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