Featured Research

from universities, journals, and other organizations

Fast, Inexpensive Sensors? Gel Changes Color On Demand

Date:
October 25, 2007
Source:
Massachusetts Institute of Technology
Summary:
MIT researchers have created a new structured gel that can rapidly change color in response to a variety of stimuli, including temperature, pressure, salt concentration and humidity. A critical component of the structured gel is a material that expands or contracts when exposed to certain stimuli. Those changes in the thickness of the gel cause it to change color, through the entire range of the visible spectrum of light.

Photonic gel crystals demonstrate the 'tunability' of materials made from alternating layers of hard and soft polymers. The soft polymers are easily swollen with liquid or vapor causing the materials to reflect different colors of light based on the way their molecules are chemically 'tuned.'
Credit: Photo by Donna Coveney / Courtesy of MIT

MIT researchers have created a new structured gel that can rapidly change color in response to a variety of stimuli, including temperature, pressure, salt concentration and humidity.

Among other applications, the structured gel could be used as a fast and inexpensive chemical sensor, says Edwin Thomas, MIT's Morris Cohen Professor of Materials Science and Engineering. One place where such an environmental sensor could be useful is a food processing plant, where the sensor could indicate whether food that must remain dry has been overly exposed to humidity.

A critical component of the structured gel is a material that expands or contracts when exposed to certain stimuli. Those changes in the thickness of the gel cause it to change color, through the entire range of the visible spectrum of light.

Objects that reflect different colors depending on which way you look at them already exist, but once those objects are manufactured, their properties can't change. The MIT team set out to create a material that would change color in response to external stimuli.

"We wanted to develop something that was 'tunable,'" said Thomas, who is head of MIT's Department of Materials Science and Engineering.

To do that, they started with a self-assembling block copolymer thin film made of alternating layers of two materials, polystyrene and poly-2-vinyl-pyridine. The thickness of those layers and their refractive indices determine what color light will be reflected by the resulting gel.

By keeping the thickness of the polystyrene layer constant and altering the thickness of the poly-2-vinyl-pyridine layer with external stimuli such as pH and salt concentration, the researchers were able to change the gel's color in fractions of a second.

"This is an ingenious and easy-to-implement method for making photonic materials whose optical properties can be readily tuned over a wide range," said Andrew Lovinger, director of the Polymers Program at the National Science Foundation, which funded this research.

The key to manipulating the thickness of the poly-2-vinyl-pyridine (2VP) layer is to give the nitrogens on each segment of the 2VP block a positive charge, yielding a polyelectrolyte chain that can swell to more than 1,000 percent its volume in water.

If the charges along the chain's backbone are electrically shielded from each other, for example by adding a high concentration of salt ions to the water that has permeated the gel, the 2VP chains collapse into disordered tangles, like balls of string. When the salt ions are washed away, the 2VP positive charges again repel each other and the chain extends, causing each 2VP layer to expand and the material to reflect a different color.

Because the diblock polymer film is a one-dimensional periodic stack, swelling is limited to one dimension, yielding a color shift of 575 percent in the reflected wavelength, a dramatic improvement over earlier color-changing gels that are made of charged colloids in a 3D lattice structure. Those gels expand in three dimensions, giving a much smaller range of color change.

The new gels are also sensitive to changes in pressure, humidity and temperature. "You can use mechanical or chemical forces to get really big responses, going through the entire range of light from ultraviolet (300 nanometers) to infrared" (1600 nm), Thomas said.

The research team is also working on a gel that changes color in response to applied voltages.

Thomas is senior author of a paper on the work to be published in the Oct. 21 online edition of Nature Materials.

The lead author of the Nature Materials paper is former MIT postdoctoral associate Youngjong Kang, now a professor at Hanyang University in Seoul, Korea. Other authors are Joseph Walish and Taras Gorishnyy, MIT graduate students in materials science and engineering.

The work was funded by the Defense Advanced Research Projects Agency and the National Science Foundation.


Story Source:

The above story is based on materials provided by Massachusetts Institute of Technology. Note: Materials may be edited for content and length.


Cite This Page:

Massachusetts Institute of Technology. "Fast, Inexpensive Sensors? Gel Changes Color On Demand." ScienceDaily. ScienceDaily, 25 October 2007. <www.sciencedaily.com/releases/2007/10/071021142334.htm>.
Massachusetts Institute of Technology. (2007, October 25). Fast, Inexpensive Sensors? Gel Changes Color On Demand. ScienceDaily. Retrieved July 22, 2014 from www.sciencedaily.com/releases/2007/10/071021142334.htm
Massachusetts Institute of Technology. "Fast, Inexpensive Sensors? Gel Changes Color On Demand." ScienceDaily. www.sciencedaily.com/releases/2007/10/071021142334.htm (accessed July 22, 2014).

Share This




More Matter & Energy News

Tuesday, July 22, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Government Approves East Coast Oil Exploration

Government Approves East Coast Oil Exploration

AP (July 18, 2014) The Obama administration approved the use of sonic cannons to discover deposits under the ocean floor by shooting sound waves 100 times louder than a jet engine through waters shared by endangered whales and turtles. (July 18) Video provided by AP
Powered by NewsLook.com
Sunken German U-Boat Clearly Visible For First Time

Sunken German U-Boat Clearly Visible For First Time

Newsy (July 18, 2014) The wreckage of the German submarine U-166 has become clearly visible for the first time since it was discovered in 2001. Video provided by Newsy
Powered by NewsLook.com
Obama: U.S. Must Have "smartest Airports, Best Power Grid"

Obama: U.S. Must Have "smartest Airports, Best Power Grid"

Reuters - US Online Video (July 17, 2014) President Barak Obama stopped by at a lunch counter in Delaware before making remarks about boosting the nation's infrastructure. Mana Rabiee reports. Video provided by Reuters
Powered by NewsLook.com
Crude Oil Prices Bounce Back After Falling Below $100 a Barrel

Crude Oil Prices Bounce Back After Falling Below $100 a Barrel

TheStreet (July 16, 2014) Oil Futures are bouncing back after tumbling below $100 a barrel for the first time since May yesterday. Jeff Grossman is the president of BRG Brokerage and trades at the NYMEX. Grossman tells TheStreet the Middle East is always a concern for oil traders. Oil prices were pushed down in recent weeks on Libya increasing its production. Supply disruptions in Iraq fading also contributed to prices falling. News from China's economic front showing a growth for the second quarter also calmed fears on its slowdown. Jeff Grossman talks to TheStreet's Susannah Lee on this and more on the Energy Department's Energy Information Administration (EIA) report. Video provided by TheStreet
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins