We analyze and explain the reversible humidity-responsive behavior of porous structured luminescent oxygen (O2) sensing films in terms of O2 permeability and optical light scattering. The luminescent O2 sensing films are composed of an O2-sensitive dye within porous polymer matrices, where the porous structure is formed via phase separation between immiscible polystyrene (PS) and polyethylene glycol (PEG). A comparison of the sensing film with a porous polymeric film without an O2-sensitive dye by in situ measurement of both the photocurrent signal and diffused reflectance under different relative humidity (RH) levels reveals the origin of the optical variations in the luminescent O2 sensing film as a function of RH. Here, the hygroscopic PEG surrounded by the PS matrix swells and fills up the pores as the RH increases, which mainly tunes the optical scattering property of the porous polymeric films, and the variation in light scattering of the porous polymeric films is explained by Mie scattering theory. By considering and analyzing the humidity response in luminescent O2 sensing films in the aspects of fabrication processes and experimental systems as well as the hydration property of the materials, this study can provide fundamental insights into the cross-sensitivity of optical O2 sensors to humidity. Moreover, the fully reversible humidity-driven tuning of the light scattering properties in porous polymeric films allows various applications, such as dual monitoring of O2 and RH in wearable sensors, responsive coating or smart windows, that require optical tuning without extra energy.
Bibliographical noteFunding Information:
This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (grant number: 2018R1A2B6001390 )
© 2019 Elsevier B.V.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Surfaces, Coatings and Films
- Metals and Alloys
- Electrical and Electronic Engineering
- Materials Chemistry