MSGID: 1:317/3 6442117d   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    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.   
      
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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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