Novel optoelectronic sensing system for thin polymer films glass transition investigation

The glass transition zone of thin polymer films on silica substrates has been investigated by using a novel optoelectronic integrated sensor involving refractive index and temperature simultaneous measurements. The sensor design is based on the deposition of a thin polymer film on the distal end of a standard optical fiber. Direct reflectometric interrogation and fiber Bragg grating operations have been used to simultaneously retrieve information about the refractive index variation over the glass transition region revealed by a temperature ramping. The glass transition has been identified by measuring the change of thermo-optic coefficient in cooling down experiments. The comparison between refractive index and standard calorimetric analysis has been carried out to test the optoelectronic integrated sensor reliability. The proposed sensing system has been demonstrated able to measure the glass transition temperature of thin polymer films. Moreover systems and procedures can be readily implemented to investigate the effect of polymeric sample finite size and specific energetic interactions on the glass transition zone.