In the peel zone: tape's electric gooeyness.

Peeling a strip of adhesive tape off a smooth surface is a violent process. As the adhesive stretches into strands, or fibrils, that suddenly snap apart, electrical activity is generated at the tape-surface juncture, often accompanied by a flickering glow visible in a darkened room.

Now, J. Thomas dickinson and his coworkers at Washington State University in Pullman have investigated the microscopic details of what happens when someone strips a common type of household adhesive tape from a polished copper surface.

The researchers discovered that the electrical current generated by the peeling tape fluctuates erratically. Moreover, the tape's initially smooth but sticky surface ends up pitted with cavities having a wide range of sizes.

"The dance of fibril detachment occurring across the entire width of the tape is a chaotic process," Dickinson suggests. "Thus, the forces acting on the adhesive...result in rich void and fibril formation...that greatly influences the way tape peels."

The researchers report their findings in the November JOURNAL OF ADHESION SCIENCE AND TECHNOLOGY.

When adhesive tape comes into contact with a surface, electrons shift from one material to the other to give them opposite electrical charges. The attraction between these oppositely charged surfaces contributes to the adhesive bond.

Peeling stresses the adhesive, creating little cavities in the material. As the process continues, the walls of the cavities stretch into fibrils. At the same time, measurable electrical discharges occur between the electrically charged tape and the metal surface near these cavities. Measurements of the resulting electrical currents reveal details of the peeling process on time scales down to nanoseconds.

"The more fibril formation and stretching that you get, the stickier the adhesive is," Dickinson says. Hence, a large proportion of the energy required to peel a strongly adhering tape goes into stretching the fibrils and working the gooey adhesive.

This research represents an extension of an earlier effort to study cracking and fracture in brittle materials (SN: 5/4/91, p.279). Fractures may also generate electricity and light.