In Situ Monitoring of Non-Fickian Liquid-Liquid Diffusion with a High Space-Time Resolution Fiber-Integrated Plasmonic Sensor

作者：Huang, Rongtao; Long, Li; Yang, Haiyao; Chen, Yuxin; Deng, Qiurong; Ju, Wenbo; Li, Zhiyuan^*

来源：ACS Photonics, 2024, 11(2): 780-788.

DOI：10.1021/acsphotonics.3c01713

• liquid-liquid diffusion
• non-Fickian diffusion
• optical fiber
• plasmonicsensing
• in situ monitoring

Liquid-liquid diffusion is a complex but important process, for which there is still no perfect theory. Many experimental methods have been proposed to measure the liquid-liquid diffusion coefficient, but none of them can accurately monitor the diffusion process with a large space-time range and high spatial resolution. Here, we propose a method of point-to-point concentration detection by scanning an optical fiber microscale plasmonic sensing probe in liquid to in situ monitor the diffusion process of water and 50% glycerol solution. By this method, we have measured the concentration space-time diagram in the time range of 24 h and spatial range of similar to 14.3 mm with a resolution of 15.2 mu m. From this, we have observed a non-Fickian phenomenon where the diffusion process appears as a time-dependent shift of the diffusion layer superimposed on its Fickian diffusive broadening and explain it by a non-Fickian diffusion model constructed by introducing the equivalent surface tension effect into the Fickian diffusion model. It has demonstrated the practicability and superiority of the high space-time resolution probe scanning method for in situ monitoring of various natural diffusion processes and disclosing new diffusion laws.