Paradoxical peeling patterns.

Processes ranging from fracture of crystals to peeling of tape have been known for many decades to emit light through a mechanism believed to be associated with electrical charging of separating surfaces. This topic, broadly termed fractoluminescence, has been proposed to be involved in several remarkable phenomena, including medical diagnostics and the generation of X-rays in the lab and earthquake lightning in nature. Here we add the paradoxical finding that two separating surfaces produce entirely different charge patterns, despite originating from the same interface. Further, we report the discovery of a rich variety of new and unexplained patterns, and we examine the hypothesis that the patterns are produced by migration of either polar or non-polar discharge ions onto contact-charged surfaces. This hypothesis may first explain prior findings that charge patterns can extend far beyond points of contact, and second suggests that the ultimate charge imparted on surfaces depends both on well-characterized mechanisms of surface potential and on highly variable discharge ions in the surrounding environment.