Rheology of novel photosensitive viscoelastic trimeric cationic surfactant/trans-ortho-methoxycinnamic acid micellar solutions

Photosensitive micellar solutions of mixed surfactants and photosensitive additives have gained much interest. However, there are no reports on photosensitive micellar solutions containing trimeric cationic surfactant. In the study, novel photosensitive viscoelastic micellar solutions consisting of trimeric cationic surfactant (TEC) and trans-ortho-methoxycinnamic acid (trans-OMCA) were investigated. This study utilized rheology, UV–vis spectroscopy, and cryo-TEM to investigate the photo-responsive behavior and mechanism of the TEC/trans-OMCA micellar solutions. Rheological studies revealed that the concentration of TEC and trans-OMCA, as well as temperature, significantly affected the viscoelastic properties of the micellar solutions. Furthermore, the Carreau and Maxwell models might be used to characterize the flow curves and viscoelasticity of the micellar solutions, respectively. Notably, TEC/trans-OMCA micellar solutions exhibited excellent light-induced thinning characteristic, with the optimal performance at a mass ratio of φ = 0.5. After UV irradiation, the zero-shear viscosity of TEC/trans-OMCA (0.6/0.3 wt%) micellar solution was reduced by 352 times, while the viscoelasticity and the area of hysteresis loops were significantly reduced. This drastic change in the rheological characteristics of the micellar solutions could be attributed to the photoisomerization of trans-OMCA and the resulting changes in the internal microstructure of the solutions. Moreover, the viscosity of the micellar solutions diminished as the temperature increased, with the remaining viscosity of the TEC/trans-OMCA (1.0/0.5 wt%) micellar solution at 36.4 mPa s at 95°C. This study expands on the potential utilization of oligomeric surfactants in the construction of photorheological viscoelastic fluids.