Integrated resonant structure for colloidal dispersion stability: development of a resonant optical zetameter

Long-term storage of colloidal solutions presents significant challenges in maintaining the physical and mechanical properties of manufactured products over extended periods. Ensuring stability is critical for agro-alimentary products, pharmaceutical formulations, and petroleum applications to preserve product quality and longevity during storage. Monitoring the stability of colloidal dispersions is essential for anticipating potential degradation over time. This study explores the evaluation of stability criteria using quasi-surface resonant analysis. Specifically, the zeta potential of colloidal solutions is investigated via resonant optical parameter, the Free Spectral Range (FSR), to distinguish between stable and unstable dispersions. For this purpose, sensors based on organic UV210 Micro-Resonators (MRs) were fabricated using deep UV photolithography. These MRs were integrated into an optical test platform, enabling real-time data collection with a spectrometer and dedicated MATLAB processing. The study focuses on black carbon nano powders dispersed in water and in water plus an anionic surfactant (Sodium Dodecyl Sulfate, SDS). The findings show that unstable solutions exhibit an increasing FSR over time, which is indicative of sedimentation, whereas stable dispersions maintain a constant FSR. These results are validated through complementary rheological and zeta potential measurements, establishing a clear correlation between FSR variations and colloidal dispersion stability. This study demonstrates the potential of resonant optical measurements as a novel tool for assessing colloidal dispersion stability, functioning as a “zetameter” on a surfacic platform.