Investigation on the aggregation behavior of photo-responsive system composed of 1-hexadecyl-3-methylimidazolium bromide and 2-methoxycinnamic acid

Abstract

A novel fluid system composed of 2-methoxycinnamic acid (trans-OMCA) and 1-hexadecyl-3-methylimidazolium bromide (C₁₆mimBr) in an aqueous solution was investigated. The compounds trans-OMCA and C₁₆mimBr in an aqueous solution can self-assemble and form viscoelastic worm-like micelles. The concentrations of trans-OMCA and C₁₆mimBr have a significant influence on the rheological properties of the system. The samples were characterized by rheological measurements. The structural isomerization of trans-to-cis for trans-OMCA occurred after UV light irradiation. The transformation of the system after UV light irradiation was determined by UV-vis absorption spectroscopy, rheological measurement and cryo-TEM observation. Surface tension measurements were carried out to investigate the role of trans-OMCA and UV light in C₁₆mimBr aqueous solution. Critical aggregation concentration (cac), effectiveness of surface tension reduction (Π_cac), maximum excess surface concentration (Γ_max) and minimum area occupied per surfactant molecule (a_s) were investigated. Critical packing parameter was introduced to express the mechanism of aggregation behavior transition.