Multiscale Analysis of the Impact of the Isomerization of 4-Amine Tetraortho-Azobenzenes on the Structure and Dynamics of Tubular Micelles

High Resolution Image Download MS PowerPoint Slide A multiscale analysis of photoresponsive micellar systems based on CTAB/NaSal and 4-amine tetraortho-azobenzenes (AzoCH 3 and AzoCl) was carried out to elucidate how molecular photoisomerization modulates micellar morphology, mesoscopic organization, and macroscopic dynamics in the semidilute regime. Under basic conditions (pH 11), CTAB/NaSal solutions incorporating trans-AzoCH 3 and trans-AzoCl form well-defined wormlike micelles (WLMs), as confirmed by TEM and molecular dynamics simulations, which reveal the presence of tubular structures. Dynamic light scattering (DLS) measurements indicate that these systems lie within the semidilute–entangled regime, where collective hydrodynamic behavior dominates over individual micellar dimensions, in agreement with viscosity measurements. Upon UV irradiation at 360 nm, trans–cis photoisomerization of the azobenzenes induces a pronounced disruption of the WLM network, leading to partial collapse and fragmentation of tubular structures, as evidenced by HR-TEM imaging and simulations. Despite this significant structural rearrangement, DLS measurements reveal no substantial change in the hydrodynamic correlation length, indicating that the system remains in the semidilute regime, consistent with the slight decrease in viscosity while preserving shear-thinning behavior. Thermal cis -to- trans isomerization kinetics were monitored by UV–vis spectroscopy and were well described by monoexponential behavior, confirming reversible photosensitivity within the micellar environment. These results demonstrate that azobenzene photoisomerization can modulate micellar morphology without altering the overall concentration regime, highlighting a decoupling between local micellar structure and mesoscopic collective dynamics. This behavior underscores the robustness of semidilute wormlike micellar networks and their potential for applications in light-responsive soft materials.