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Honolulu, Hawaii, United States, 2006/10/24 - New research shows that waterborne PSAs containing single-wall carbon nanotubes meet the requirements of environmental regulations while improving the adhesive performance.
Adhesives may be broadly divided in two classes: structural and pressure sensitive. To form a permanent bond, structural adhesives harden via processes such as evaporation of solvent or water (white glue), reaction with radiation (dental adhesives), chemical reaction (two part epoxy), or cooling (hot melt). In contrast, pressure sensitive adhesives (PSAs) form a bond simply by the application of light pressure to attach the adhesive to the adherend. PSAs adhere instantly and firmly to nearly any surface under the application of light pressure, without covalent bonding or activation. Waterborne pressure-sensitive adhesives solve the problem of meeting environmental regulations that forbid the emission of volatile organic compounds in manufacturing. However, often waterborne PSAs have poor adhesive performance. Another problem, particularly relevant to display technologies, is how to make an electrically-conducting material that is also flexible and optically transparent. Indium tin oxide is commonly used as a transparent electrode in displays, but it is brittle and prone to mechanical failure or scratching. Adhesives can be made electrically conductive through the addition of metal particles, but then they lose optical transparency, and their adhesiveness is diminished. New research shows that waterborne PSAs containing single-wall carbon nanotubes (SWNTs) meet the requirements of environmental regulations while improving the adhesive performance. The resulting unprecedented combination of adhesion and conductivity properties holds enormous potential for demanding applications in displays and electronics.
To achieve the maximum tack energy (i.e. energy for de-bonding), a PSA must dissipate a large amount of energy on deformation, but it must not have an elastic modulus, E, that is too high. Recent work has shown that using nanocomposite polymer films opens the door to fabricating high performance PSAs.
"These nanocomposite PSAs have it all" says Dr. Joseph Keddie, reader in Physics in the Soft Condensed Matter Group at the University of Surrey in the UK.
Keddie explains the new findings to Nanowerk: "The E of poly(butyl acrylate), which is too low to make it a good adhesive, is increased with the addition of SWNTs. At the same time, the amount of energy dissipated increases with SWNT addition. These two factors lead to an optimum SWNT concentration for achieving the maximum tack energy."
Read the full article on the Nanowerk website.
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By Michael Berger, Copyright 2006 Nanowerk, LLC