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Scientists have succeeded in creating a glue with fickle stickiness. Described in the current issue of the Journal of the American Chemical Society, the smart adhesive becomes less clingy at higher temperatures but regains its tackiness once it cools.
To make their adjustable glue, Sureurg Khongtong and Gregory Ferguson of Lehigh University started with a standard synthetic rubber. They then added an oxidizing agent to the material. This introduced so-called functional groups that are attracted to the outer coating on aluminum oxide and cause the two materials to stick together at room temperature. When the material is heated, however, the polymer chains of the rubber contract, pulling aluminum-loving carboxylic acid groups away from the surface. As a result, the bond between the metal and the polymer loosens such that the adhesion between the two surfaces is 44 percent less at 80 degrees Celsius than it is at room temperature.
After the rubbery glue returns to cooler temperatures, it regains its former sticking prowess, albeit slowly. According to the report, it takes approximately 40 hours to recover the initial level of adhesion, and this reversibility persists through multiple heating and cooling cycles. The polymer also has another interesting property: as its stickiness lessens, it becomes more water-repellent. The authors note that similar systems, in which adhesion is responsive to environmental conditions, could be put to use as barrier films to prevent buildup on underwater surfaces or as a means of controlling cell adhesion for surgical applications.
