Ferguson and Khongtong modified a 1-4 polybutadiene, a standard synthetic rubber, by treating it with aqueous permanganate, an oxidizing agent that triggers formation of carboxylic acids and other functional groups attracted to aluminum oxide. At room temperature, the molecular chains of the treated rubber extend and hook onto the metal oxide layer, Ferguson says. When heated, the molecular chains resume their disordered higher-entropy state, pulling away from the surface and weakening the polymer-metal bond.
When they heated the interface to 80 C and then quickly cooled it to room temperature, the researchers observed a 44 percent reduction in the adhesion bonding the two surfaces, confirming the temperature dependence of the bond. The interface regained its original stickiness 40 hours after the return to room temperature, and the reversibility persisted through multiple heating and cooling cycles. The scientists also report that the polybutadiene becomes more hydrophobic when it loses its adhesion at elevated temperature.