Multi-modal sensing using photoactive thin films

Abstract

The need for a reliable prognosis of the health of structural systems has promoted the development of sensing technologies capable of simultaneously detecting multiple types of damage. However, conventional sensors are designed to only measure a specific structural response (e.g., strain, displacement, or acceleration). This limitation forces one to use a wide variety of sensors densely instrumented on a given structure, which results in high overhead costs and requires extensive signal processing of raw sensor data. In this study, a photoactive thin film that has been engineered for multi-modal sensing to selectively detect strain and pH is proposed. In addition, the thin film is self-sensing in that it does not require external power to operate. Instead, light illumination causes the photoactive film to generate an electrical current, whose magnitude is directly related to applied strains (for deformations, impact or cracks) or pH (as a precursor of corrosion). First, the thin films were fabricated by spin-coating photoactive and conjugated polymers like poly(3-hexylthiophene) (P3HT). The thin film was also encoded with pH sensitivity by integrating polyaniline (PANI) as one component within the multilayered film architecture. Second, the optical response of the P3HT and PANI thin films subjected to applied strains or pH was characterized using absorption spectroscopy. Lastly, it was also verified that the thin films could selectively sense strain or pH depending on the wavelengths of light used for sensor interrogation.