Thermal effects on the VOC-sensitive polydimethylsiloxane holographic gratings

The imperative for monitoring volatile organic compounds (VOCs) emerges from their harmful impact on human health when inhaled excessively over a long term. Polydimethylsiloxane (PDMS), valued for its transparency and excellent flexibility, has already been demonstrated as a promising biocompatible and cost-effective transducer for optical VOCs sensing. Moreover, it facilitates further functionalisation with adsorbing materials to enhance sensitivity and selectivity for specific VOCs detection. We fabricated and examined PDMS-based surface diffraction gratings after exposure to selected VOCs, demonstrating different response for polar and non-polar molecules. Investigated gratings were prepared by replicating sinusoidal surface relief structures inscribed in acrylamide photopolymer using a holographic recording method. Our study is primarily concerned with gratings featuring a period of 8.4 ± 0.2 micrometres and an amplitude of 585 ± 32 nanometres. The proposed sensing method relies on diffraction efficiency modulations induced by the analyte causing a dimensional change in the PDMS layer and altering its refractive index by filling its pores. Here, we delve deeper into the intrinsic properties of PDMS that influence diffraction efficiency when the surrounding temperature is varied. Any temperature sensitivity may significantly impact the response of the grating to VOCs in a thermally unstable environment. The implications of this study are particularly important for sensor applications for air quality monitoring, as they are susceptible to variations stemming from seasonal influences throughout the year. The variation of the diffraction efficiency of the surface relief PDMS gratings was studied in the temperature range 20 to 60 °C. It was observed that diffraction efficiency alters with the amplitude of diffraction efficiency change in the range of 0.08-0.42%.