Mechanoluminescence of poly(methyl methacrylate)

sA short-term emission induced at the instant of the mechanical fracture of PMMA in a high vacuum was experimentally detected. The kinetics of mechanoluminescence is presented by two separate stages: the first stage is related to the propagation of the main crack at a subsonic speed, whereas the second stage is provided by the cracking of a freshly formed fracture surface upon its rapid cooling and a concomitant vitrification. Synchronous processes of mechanoluminescence emission and crack nucleation and propagation allow one to assume that this behavior is exclusively provided by the rupture of polymer chains and, hence, may be used as a method for controlling the nucleation and growth of brittle cracks in polymers. A carbonyl group in a polymer unit is shown to be responsible for the luminescence in PMMA. Spectral and kinetic studies of photoluminescence in PMMA show the existence of both fluorescent and phosphorescent components of light emission. However, the time characteristics of mechanoluminescence exclusively attest to its fluorescent nature.