Revealing molecular diffusion dynamics in polymer microspheres by optical resonances
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Updated: Jul 31, 2025

Fabrication of Polymer Microspheres for Optical Resonator and Laser Applications
Published on: June 2, 2017
Jiawei Wang1, Jin Li1, Shengqi Sun1
1School of Electronic and Information Engineering, Harbin Institute of Technology, Shenzhen 518055, China.
Abstract:
Understanding the diffusion of small molecules in polymer microsystems is of great interest in diverse fundamental and industrial research. Despite the rapidly advancing optical imaging and spectroscopic techniques, entities under investigation are usually limited to flat films or bulky samples. We demonstrate a route to in situ detection of diffusion dynamics in polymer micro-objects by means of optical whispering-gallery mode resonances. Through mode tracking, interactions between solvent molecules and polymer microspheres, including sorption, diffusion, and swelling can be quantitatively analyzed. A turning point of mode response is observed, while the diffusion exceeds the sub-wavelength-thick outermost layer as the radial extent of resonances and starts penetrating the inner core. The estimated solubility in the glassy polymer is consistent with the predicted value using Flory-Huggins theory. Besides, the non-Fickian contribution is analyzed in such a glassy polymer-penetrant system. Our work represents a high-precision and label-free approach to describing characteristics in diffusion dynamics.
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