Scientists at Nagoya University have developed a new way to make stimuli-responsive materials in a predictable manner. They used this method to design a new material, a mixture of carbon nanorings and iodine, which conducts electricity and emits white light when exposed to electricity. The team’s new approach could help generate a range of reliable stimuli-responsive materials, which can be used in memory devices, artificial muscles and drug delivery systems, among other applications.
Stimuli-responsive materials alter their own properties in response to external stimuli, such as photo-irradiation, heat, pressure and electricity. This feature can be controlled for a wide range of uses, such as in optical discs, computer memories and displays, as well as artificial muscles and drug delivery systems.
Researchers have been working to develop new stimuli-responsive materials in a predictable fashion. However, it has been extremely difficult to design and control the complex molecular arrangements of the materials.
Now, a simple and reliable method to synthesize stimuli-responsive materials has been developed by a team led by Nagoya University’s JST-ERATO Itami Molecular Nanocarbon Project and the Institute of Transformative Bio-Molecules (ITbM). The results of this study were recently reported in the journal Angewandte Chemie International Edition.
The ‘responsive porous host’ method takes a molecule with a porous framework and binds to it a ‘guest’ molecule that is likely to react to external stimuli (Figure 1a). In this case, the team found that cycloparaphenylene (CPP), a hydrocarbon molecule composed of 10 para-connected benzene rings, made an ideal host when combined with iodine (I). Iodine situated itself inside the porous carbon rings, and reacted to electric stimulation. Not only did it conduct electricity, it also emitted a white light, which is unusual (Figure 1b). Typically, many other components are required to obtain the white color. This shows the potential of the new material, CPP-I, for next generation illumination systems.
“This ‘responsive porous host’ approach is expected to be applicable to different stimuli, such as photo-irradiation, heat application and pH change, and open the path for devising a generic strategy for the development of stimuli-responsive materials in a controllable and predictable fashion,” said Dr. Hirotoshi Sakamoto, a group leader of the JST-ERATO project.
Figure 1. New synthetic approach for electric-stimuli-responsive materials. a) Strategy to develop electric-stimuli-responsive materials using porous solid. b) Electric-stimulus-induced generating electric conductivity and white light fluorescence of [n]CPP-I.
Synthesizing the material is surprisingly simple — the researchers mixed carbon nanorings (CPP) and iodine together, and let it dry. X-ray crystallography confirmed that the iodine molecules line up inside the hollow core of the aligned nanorings (Figure 2).
Figure 2. X-ray structure of CPP-I, carbon atoms are colored in gray and iodine atoms are colored in purple.
The team tried several variations of the mixture, changing the number of carbon nanorings, and found that 10 rings led to the most dynamic iodine atom movement and the most sensitive response to external environmental changes.
When a direct current was applied to CPP-I, the bulk resistivity of the sample became approximately 380 times lower, indicating that it conducted electricity rather than resisting electrical transmission. The bulk resistivity in mixtures with 9 or 12 nanorings did not decrease nearly as much (Figure 3). These results show that pore size in the nanoring assembly controls the response to electrical stimulation.
Figure 3. The plots of bulk resistivity of [n]CPP-I versus the time elapsed under voltage bias application.
“One of the most difficult parts of this research was to investigate how the electric conductivity of CPP-I is turned on by electric stimuli,” said Dr. Noriaki Ozaki, a postdoctoral researcher of the JST-ERATO project. “Although it only took us about three months to synthesize the molecule and discover its electric-stimuli-responsive properties, it took another year to discover the origin of its properties.”
The team finally figured out how the electric conductivity of CPP-I is turned on by electric stimuli, using X-ray absorption near-edge spectroscopy (XANES), Raman spectroscopy, and fluorescence spectroscopy. These analyses showed that the iodine atoms in the carbon nanorings form extended polyiodide chains when stimulated by electricity, which gave the material electrical conductivity.
Figure 4. Photographic images of CPP-I before (left) and after (right) the voltage bias application.
The researchers also discovered that electric stimuli can switch the photoluminescence color of CPP-I from a green-blue color to a white color (Figure 4). White luminescence means that the fluorescence spectrum of CPP-I covers the whole visible light range. Spectral broadening is attributed to the irregular distribution of the electronic structures of CPPs, which is caused by the formation of polyiodide chains (Figure 5). The white luminescence of CPP-I is a rare example of white illumination material from a single molecular assembly; white light emission is usually achieved by mixing several components of different colors.
“We were really excited to develop this simple yet powerful method to achieve the synthesis of external-stimuli-response materials,” said Professor Kenichiro Itami, director of the JST-ERATO project and center director of ITbM.
Figure 5. Schematic illustration of polyiodide chains upon application of electric stimuli.
The Latest on: Stimuli-responsive materials
Summer Spotlight: Victoria Kogan of Women’s Tennis
on July 16, 2018 at 9:06 am
The biomedical engineering major is working on a project called “Bio-inspired Multi-functional Stimuli Responsive Hybrids,” inspired ... to eventually be able to create the most optimized material(s). ... […]
These Futuristic Bandages Monitor and Automatically Treat Wounds
on July 10, 2018 at 4:56 am
The paper states A stimuli‐responsive drug releasing system comprising of a hydro ... In order to make the bandage cheaper and reusable, the research team used 3D-printed materials and detachable laye... […]
Smart Materials Market by Type - Global Opportunity Analysis and Industry Forecast, 2014-2022
on June 13, 2017 at 6:18 am
Portland, OR -- (SBWIRE) -- 06/13/2017 -- Smart Polymers, Also Known As Stimuli Responsive Materials Or Intelligent Materials, Are High Performance Polymers That Respond To The Stimuli Or Changes In T... […]
Multi stimuli-responsive nanocapsules selectively deliver drugs to exactly where they are needed
on September 20, 2016 at 5:00 pm
The nanoparticles developed by Chaobin He, Zibiao Li and their colleagues at the A*STAR Institute of Materials Research and Engineering are unusual in that they combine multiple stimuli-responsive beh... […]
Emerging applications of stimuli-responsive polymer materials
on March 17, 2015 at 5:00 pm
Frequency of updates: In most cases, our metrics data is updated hourly, In some cases, such as page views, the data is not available the first 48 hours after an article is published. Single number co... […]
Stimuli-responsive drug delivery system prevents transplant rejection
on August 13, 2014 at 12:28 pm
"Nearly every disease has an inflammatory component. Thus we believe the materials we have developed could be used for localized treatment of multiple inflammatory diseases." Added Praveen Kumar Vemul... […]
Research and Markets: A Handbook of Stimuli-Responsive Materials - Providing Comprehensive Coverage of Developments in Advanced Technologies
on June 28, 2011 at 4:45 pm
DUBLIN--(BUSINESS WIRE)--Research and Markets (http://www.researchandmarkets.com/research/8894d2/handbook_of_stimul) has announced the addition of John Wiley and Sons Ltd's new book "Handbook of Stimu... […]
Stimuli-responsive polypeptide vesicles by conformation-specific assembly
on June 30, 2009 at 5:00 pm
Departments of Materials and Chemistry, University of California, Santa Barbara, California 93106, USA Department of Materials Science and Engineering and Delaware Biotechnology Institute, University ... […]
via Google News and Bing News