Novel optoelectronic sensing system for thin polymer films glass transition investigation

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