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Honolulu, Hawaii, United States, 2006/09/28 - ‘Smart’ polymers can recognize a stimulus as a signal and then significantly alter for instance their chain conformation in response to small changes in the environmental conditions.
Imagine to catch one, or a few, molecules dissolved in water, lock them up in a cage with a diameter of a few hundred nanometers, and keep them locked for a given length of time. Then bring these containers with the „captive” molecules to places within the solution where you want to have them, and release the captured molecules from their captivity on chemical command. Or simply keep the molecules in the cage „prison” locked up, add a few more different molecules to water, and watch their chemical reaction following movement across the container wall in „solitary” confinement within the containers with the molecules already captured. Such dreams of nanotechnologists have come much closer to reality as a result of a discovery made by a team of researchers, lead by Professor Julius Vancso of the University of Twente, from the MESA+ Institute for Nanotechnology collaborating with scientists of the Max Planck Institute of Colloids and Interfaces in Golm, Germany.
Dr. Vancso explained his team's findings to Nanowerk: "We made micro- and nanocontainers, using special polymers, containing iron in their main chain, which respond reversibly and alter their number of electrons to changes triggered by oxidation and reduction using chemical agents. Upon changes of the number of electrons on iron atoms in the polymer chains, which make up the wall of the nanocontainers, the walls can be made either open (permeable), or closed (non-permeable) for other molecules which would move into the containers or out of the containers, depending on the previous loading of the containers."
‘Smart’ polymers can recognize a stimulus as a signal and then significantly alter for instance their chain conformation in response to small changes in the environmental conditions. Researchers are very interested in molecular structures that are composed of such materials, with the ability to be triggered to contract or expand in a controlled fashion.
Conventional, organic polyelectrolyte-based microcapsules have limitations in some significant applications due to their slow response to trace amounts of trigger and restrictions on the choice of stimuli. Scientists found that electrochemical stimuli are very promising, though they requires the construction of capsules with redox-active compounds.
Vancso and his collaborators used water soluble PFS - poly(ferrocenylsilanes) - polycations and polyanions. These compounds belong to the rare class of main-chain organometallic polyelectrolytes, which have recently been reported. They all bear certain charges on the polymer side groups so that they can be used in the electrostatic layer-by-layer (LBL) self-assembly process to form multilayer films and hollow capsules with defined structure and function due to the molecular characteristics of the organometallic main chain.
Read the full article on the Nanowerk website.
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By Michael Berger, Copyright 2006 Nanowerk LLC.