Study on rheology of a novel UV-light sensitive trimeric anionic–cationic surfactant/trans-o-methoxycinnamic acid micellar system

Two novel UV photosensitive micellar systems, trimeric dodecyl anionic–cationic surfactant (TDCC)/trans-OMCA, and trimeric cetyl anionic–cationic surfactant (TCCC)/trans-OMCA, were successfully synthesized by using two different carbon chain length trimeric anionic–cationic surfactants (TACS, including TDCC and TCCC) and the photosensitive additive trans-o-methoxycinnamic acid (trans-OMCA). The incorporation of trans-OMCA resulted in a peak in the zero shear viscosity (η 0) of the system at pH = 6.17–6.61. The flow behaviour of the TACS/OMCA system was well described by the Carreau-Yasuda model. Prior to UV irradiation, the TCCC/trans-OMCA system exhibited pronounced shear thinning, thixotropic, and viscoelastic properties. After UV irradiation at 365 nm, the isomerization of trans-OMCA to cis-OMCA caused the disruption of the network structures, leading to a significant decrease in the thixotropic and viscoelastic properties, resulting in a decrease in viscosity. The viscosity reduction rate of the TCCC/trans-OMCA system reached 99 %. The influence of the hydrophobic carbon chain length on the UV responsiveness was also investigated. The TDCC/trans-OMCA system exhibited an 86 % decrease in η 0 after UV irradiation, highlighting the favorable effect of longer hydrophobic tail chains in improving the UV responsiveness of the micellar system. The UV light kinetics of the TCCC/trans-OMCA solution were studied and a rheological model was developed to accurately describe the viscosity changes. The TCCC was found to predominantly exhibit cationic characteristics at pH = 6.17–6.61. In this pH range, the 2 wt% TCCC/0.12 wt% NaSal system exhibited excellent viscoelasticity, and the addition of trans-OMCA disrupted the network structure resulting in a decrease in viscosity. After UV irradiation, the viscosity of the system increased by 2.5 times, confirming the potential of the TCCC/NaSal/trans-OMCA micellar system as a UV thickener.