Photorheological Ionic Liquids

Smart Fluid System Dually Responsive to Light and Electric Fields: An Electrophotorheological Fluid

Electrophotorheological (EPR) fluids, whose rheological activity is dually responsive to light and electric fields (E fields), is formulated by mixing photosensitive spiropyran-decorated silica (SP-sSiO₂) nanoparticles with zwitterionic lecithin and mineral oil. A reversible photorheological (PR) activity of the EPR fluid is developed via the binding and releasing mechanism of lecithin and merocyanine (MC, a photoisomerized form of SP) under ultraviolet (UV) and visible (VIS) light applications. Moreover, the EPR fluid exhibits an 8-fold higher electrorheological (ER) performance compared to the SP-sSiO₂ nanoparticle-based ER fluid (without lecithin) under an E field, which is attributed to the enhanced dielectric properties facilitated by the binding of the lecithin and SP molecules. Upon dual application of UV light and an E field, the EPR fluid exhibits high EPR performance (ca. 115.3 Pa) that far exceeds its separate PR (ca. 0.8 Pa) and ER (ca. 57.5 Pa) activities, because of the synergistic contributions of the PR and ER effects through rigid and fully connected fibril-like structures. Consequently, this study offers a strategy on formulation of dual-stimuli responsive smart fluid systems.

UV and NIR dual-responsive self-assembly systems based on a novel coumarin derivative surfactant

Controllable self-assembly systems have attracted increasing attention in both the academic and industrial fields recently. Herein, we designed and synthesized a new photo-degradable anionic surfactant (PAS) with a coumarin group which could be degraded by both UV and NIR light. Thus, the micelles that are formed by sodium salts of PAS (PAS-Na) could be broken controllably under UV or NIR irradiation. Surface tension measurements, DLS, and Cryo-TEM were adopted to investigate the formation and disruption of PAS-Na micelles. PAS could also form wormlike micelles and vesicles when they co-assembled with common surfactant tetradecyldimethylamine oxide (C₁₄DMAO). These wormlike micelles and vesicles could be degraded by UV and NIR irradiation due to the participation of PAS. Accordingly, the rheology properties of the wormlike micelles and vesicles were also changed significantly. Finally, the stimulus-responsive system was used to control the diffusion of hydrophobic and hydrophilic molecules. And it has shown controllable release effects on both the hydrophobic and hydrophilic molecules.