Memories in Matter: Adhesive Tape as a Mechanical Comparator

Soft matter offers unique opportunities to study how history dependent systems can store, recall, and forget information. When driven with an oscillating tension, voltage, or shear strain, some systems form memories of multiple distinct amplitudes. However, most existing frameworks pertain to driving that oscillates symmetrically around an equilibrium, despite many common examples of asymmetric driving in everyday life. One such example is a strip of ordinary adhesive tape that is partially peeled off a surface and laid back down. We show that peeling tape leaves a line of strong adhesion at the turning point, which is a memory read as a spike in the force when the tape is later peeled past that point. Repeating this partial peeling by successively shorter distances can store multiple lines of strong adhesion, much as a combination lock stores a series of values. We take advantage of tape's variable adhesive strength to examine the nature of memory erasure for different tape and substrate combinations. Using the simple example of tape, we establish a generic model for multiple memories under asymmetric driving and consider the tape as a mechanical computation device that acts as a one-back comparator.