Visualization of Gas Mass Transfer by Interferometric Microsphere Microscopy

In situ observation of the gas mass transfer process is crucial for the development of high-performance sensing and catalytic materials. However, visualizing gas distribution patterns at the micro/nano interface remains challenging due to the weak optical signal of gas molecules as well as the trade-off between high resolution and a large field of view (FOV). To overcome these limitations, we developed label-free interferometric microsphere microscopy (IMM), achieving a resolution of 50 nm within an FOV of 100 μm². A 45 μm microsphere was selected for the large-scale imaging. To improve the resolution within this large FOV, multiwavelength gas images were obtained by using frequency shift technology and fused using an algorithm. The structure-performance relationship of colorimetric gas sensors was established by analyzing the gas dynamics. The critical transition from laminar to vortical flow at micro/nano interfaces occurs at a Knudsen number (Kn) of 0.01, which depends on the size of the micropores. Laminar flow was observed at Kn = 0.008 and a micropore size of 6.3 μm. As the Kn value increased to 0.01, the micropore size corresponding to this value decreased to 4.5 μm, resulting in the formation of a vortex gas diffusion regime and improving the sensor response by 70%. The IMM shows great promise for real-time gas dynamics detection and is a powerful tool for determining the quantitative relationship between the structure and performance of functional materials.