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02/14/2017 HYU News > Academics


Transition of PDA Crystals

Professor Kim Jong-man (Department of Chemical Engineering)


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In the 21st century, nanoscience is coming into the limelight, as more sophisticated technologies are urgently in need to solve crimes or enhance the quality of life. Here is the leader of the Institute of Nano Science and Technology (INST) of Hanyang University- Kim Jong-man, professor at the Department of Chemical Engineering, who is currently leading the field of nanoscience. In the paper “Photoinduced reversible phase transition of azobenzene-containing polydiacetylene crystals,” Kim revealed how an azobenzene-containing supramolecular polydiacetylene (PDA) crystal undergoes a photo-induced reversible red-to-blue phase transition accompanied by crystal tearing.
Kim reveals the reversible phase transition that azobenzene-containing PDA crystals undergo.
Polydiacetylene, also called as PDA, is an organic polymer that conducts electricity, which is created by the polymerization of substituted diacetylene. PDA is a commonly used compound in the scientific field, considering its multiple applications- from development of organic films to immobilizations of other molecules.

Recently, Kim and his research team have found out that when azobenzene, a synthetic crystalline organic compound, is incorporated to PDAs, it showed grand responsiveness to ultraviolet (UV) radiation. “The ultimate goal of this research was to find out what kind of changes the azobenzene-containing PDA crystal undergoes when exposed to UV rays. The result was phenomenal, as crystal tearing was detected in the vulnerable areas of its crystalline structure,” said Kim.
Photo-isomerization of azobenzene is a form of light-induced molecular motion, which simply means the compound is capable of absorbing light. When azobenzene is incorporated into PDA crystals, crystal tearing occurred, along with red-to-blue color phase transition between frail crystal structures. These measured up to about 25 degrees in angle. When the UV exposure was removed, the crystalline structure returned to its original state.
The video above shows the reversible phase transition of azobenzene-containing PDA crystal, and its crystalline tearing, along with red-blue transition.
(Video courtesy of Kim)
The graph above shows the angle of crystal tearings when the UV is turned on and off. 
(Photo courtesy of Kim)

“This crystal-tearing phenomenon was a startling finding, because in the beginning, our team only expected color changes, not alternations in the structure. This six month-long experiment proved that light, such as UV rays, can be used as remote controls to regulate nano-compounds,” mentioned Kim. A remote control of nano-particles using lights is called an ‘actuator’, and Kim is hoping to enhance the sophistication of its design based on this experiment.
PDA is an intriguing compound, due to its scientifically academic characteristic and practicality. PDAs can bear several colors, mostly red and blue, which is a rare phenomenon found in an organic compound. When certain physical or chemical pressure is applied to PDAs, they usually change their color from red to blue. When the pressure is removed, the color will change back from blue to red, which is called the reversible transition phase. Using this reversibility, Kim discovered various practical applications of PDAs, such as the ‘Forged Gasoline Identification Kit’ or the 'Pore Map', which identifies inherent pore structures.
Kim explains various applications of polydiacetylenes.

“It is my ultimate goal to develop sensitive sensors using PDAs that can be applied to carbon nanotubes or lung cancer detectors,” added Kim. Carbon nanotubes are allotropes of carbon that are useful in a lot of areas, such as nanotechnology, optics, electronics and material sciences.

The lung cancer detector that Kim desires to formulate is designed based on the fact that human breaths consist of about 40 kinds of volatile organic compounds (VOC). Among the VOCs, there is a compound called toluene, which lung cancer patients possess three times more than normal people in their breaths. Based on this, Kim longs to create a kit that can verify whether a test taker is ill or not, just by breathing into the kit.
“These practical applications do have restrictions, since the area they are used for are sensitive- economically and security-wise. As a professor, I'm more interested in enhancing the academic foundation of material science, especially PDAs, for the future of nanotechnology,” said Kim.

“I want my students and trainees to become scientists, not technicians. While technicians do what they are told to do, scientists ponder upon new ideas and move forward creatively. This approach will allow the futures of our students - including science - to shine.”
"Becoming a questioning scientist, instead of a passive technician, is key to the bright future of science."

Kim Ju-hyun
Photos by Kim Youn-soo
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