A diffraction-based degradation sensor for polymer thin films

With the recent rise of organic electronics, bioelectronics, and transient devices, polymer thin films are finding prominence as substrates, functional layers and diffusion barriers. While some of these applications require degradable polymers, others necessitate materials with high stability and resistance to degradation during operation. Due to their minuscule thickness and mass, it is challenging to characterize the degradation and stability of thin films using existing techniques developed mainly for bulk materials. We introduce here a diffraction-based degradation sensor that can monitor the physical changes that take place as polymer chains are removed during the surface degradation of a polymer film without requiring expensive equipment and extensive sample preparation. To assess the degradation of a polymer film, the surface of the polymer is first patterned with a diffraction grating. This grating forms the key component of the degradation sensor, which also includes a laser and a photodetector to monitor diffraction efficiency as a function of time. When the patterned polymer surface degrades, the diffraction efficiency decreases. As validation, we use this approach to observe both enzymatic degradation of polyhydroxybutyrate films, and dissolution stability of silk. We demonstrate that the degradation sensor can monitor, with high reliability, the degradation of samples with minute mass changes, enabling qualitative and quantitative comparisons in different sample types and/or exposed to various degradation environments.