An unusual visual microcracking/healing phenomenon in polycarbonate at room temperature

Polycarbonate samples show no visible changes upon removal from boiling water. However, during a subsequent storage stage at room temperature they begin to develop visible disc-shaped microcracks whose number and size increase with time. At a certain time during the room temperature storage period a healing process begins leading in many cases to a complete visual disappearance of the microcracks. The cracking/healing phenomenon is explained in terms of water-supersaturated systems undergoing water phase-separation creating water filled microcracks. These thin water filled microcracks then lose their water to the environment during drying at room temperature, close, and visually heal.