Real-Time and Remote Isomerization Measurement of Photochromic Polymer Nanoparticles via Dynamic Speckle Pattern Analysis

We introduce dynamic speckle pattern (DSP) analysis as a remote and real-time method for monitoring the photoisomerization dynamics in photochromic polymer latex nanoparticles. A photoresponsive latex-based system is developed by physically incorporating spiropyran, a reversible photochromic compound, into a water-based polymer matrix synthesized via emulsion copolymerization of methyl methacrylate (MMA), 2-hydroxyethyl methacrylate (HEMA), and acrylamide (AAm). The resulting latex-based nanoparticles demonstrate excellent colloidal stability and reversible light-induced color switching under aqueous conditions, highlighting their suitability for smart coatings, optical sensors, and anticounterfeiting applications. The photoisomerization and nonphotoisomerization under UV exposure process is monitored in situ by acquiring time-resolved speckle patterns under controlled environmental conditions, followed by statistical analysis to quantify temporal fluctuations associated with bond reformation and network recovery. Time-resolved DSP analysis enables quantitative evaluation of both forward photoisomerization kinetics and relaxation dynamics following cessation of irradiation. These results demonstrate the intrinsic reversible switching behavior of spiropyran-integrated polymers and establish DSP analysis as a powerful in situ characterization approach for real-time investigation of dynamic photoresponsive materials.