UV-responsive micellar systems and aqueous two-phase systems based on cationic ester-containing gemini surfactant and sodium trans-ortho-methoxycinnamate

Abstract

Three ester-containing gemini surfactants (CmDEGs) were used to construct UV-responsive micellar systems with sodium trans-ortho-methoxycinnamate (trans-NaOMCA) as photo-sensitive additive. The effect of tail-chain length and spacer chain length on the UV-responsive ability was preliminarily explored. Longer tail chain and shorter spacer chain are favorable factors for enhancing UV-responsive ability. The addition of trans-NaOMCA into N,N′-bis(2-(dodecanoyloxy)ethyl)-N,N,N′,N′-tetramethyl-1,3-propane diammonium dibromide (C12DEG3) aqueous solution leads to a peak in zero-shear viscosity (η0) versus composition curve, and its further addition induces aqueous two-phase separation. For the C12DEG3/trans-NaOMCA/H2O mixed micellar systems, the UV responsiveness of significant decrease in η0 ascribes to microstructural transitions arising from the changes in counterion binding modes due to the trans-cis photoisomerization of NaOMCA. In comparison with the gemini surfactant 12-3-12, C12DEG3 has ester groups introduced in its tail chains. The introduction of ester groups leads to a significant effect on enhancing the photo-responsive ability in viscosity decrease of the constructed UV-responsive micellar systems. Furthermore, the effect of the addition of an amino acid–based surfactant sodium lauroylglutamate (SLGlu) into the C12DEG3/trans-NaOMCA/H2O mixed system on the UV-responsive behaviors was explored. In addition to UV-induced significant decrease in η0 and phase transition from aqueous two-phase systems (ATPS) to isotropic single-phase systems, the addition of SLGlu can also cause UV-induced increase in η0 and lead to richer UV-induced phase transition behaviors. The reason leading to these differences due to the presence of SLGlu was discussed based on 1H NMR spectra, molecular dynamics (MD) simulation, and molecular electrostatic potential (MEP) analysis.