A Mechanoluminescent ZnS:Cu/Rhodamine/SiO2/PDMS and Piezoresistive CNT/PDMS Hybrid Sensor: Red-Light Emission and a Standardized Strain Quantification.

We developed a hybrid strain sensor by combining mechanoluminescent ZnS:Cu/rhodamine/SiO2/PDMS composites and piezoresistive CNT/PDMS for qualitative and quantitative analysis of onsite strain. The former guarantees a qualitative onsite measure of strain with red-light emission via mechanoluminescence (ML) and the latter takes part in accurate quantification of strain through the change in electrical resistance. The PDMS matrix enabled a strain sensing in a wider range of strain, spanning up to several hundred percent in comparison to the conventional rigid matrix composites and ceramic-based ML sensors. Red-light emission would be much more effective for the visualization of strain (or stress) when ML is used as a warning sign in actual applications such as social infrastructure safety diagnosis, emergency guide lighting, and more importantly, in biomedical applications such as in the diagnosis of motility and peristalsis disorders in the gastrointestinal tract. Despite the realization of an efficient red-light-emitting ML in a ZnS:Cu/rhodamine/SiO2/PDMS composite, the quantification and standardization of strain throughout the ML has been far from complete. In this regard, the piezoresistive CNT/PDMS compensated for this demerit of mechanoluminescent ZnS:Cu/rhodamine/SiO2/PDMS composites.