Photo-responsive wormlike micellar systems based on mixed cationic/anionic surfactants and mixed photo-sensitive additives

摘要

A method to construct photo-responsive wormlike micellar systems with high photo-responsive efficiency and strong photo-responsive ability and reduced impact on the environment by mixed cationic/anionic surfactants and mixed photo-sensitive additives has been proposed. For this purpose, a cleavable cationic ester-containing gemini surfactant, NN-bis(2-(dodecanoyloxy)ethyl)-N,N,N',N'-tetramethyl-1,3-propane diammonium dibromide (C(12)DEG(3)), and five anionic biocompatible carboxylate surfactants, have been selected. The mixed photo-sensitive additives are composed of sodium trans-ortho-methoxycinnamate (trans-NaOMCA) and sodium trans-cinnamate (trans-NaCA). The mixed cationic/anionic surfactants are superior to the single cationic surfactant C(12)DEG(3) in constructing UV light-responsive wormlike micellar systems due to their stronger self-assembly ability. The molecular structure of anionic surfactant, such as the length of hydrophobic tail, the introduction of the N-methylated amide group between the hydrophobic tail and carboxylate headgroup, and the number of hydroxyl group in bile salts, is important factor influencing the self-assembly ability of the mixed systems. For single C(12)DEG(3) or the mixed cationic/anionic surfactants, the mixed photo-sensitive additives have the advantages of both trans-NaCA and trans-NaOMCA. The fast reaction rate of the trans-to-cis photo-isomerization of NaOMCA leads to the high photo-responsive efficiency of the wormlike micellar systems. The addition of trans-NaCA promotes the growth of wormlike micelles and leads to larger difference between viscosities before and after UV irradiation, demonstrating higher photo-responsive ability. The experimental results reveal that the UV light induced trans-to-cis isomerization of NaOMCA is the main reason inducing the microstructural transition from wormlike micelles to coexistence of spherical and short rodlike micelles and thus causing reduction in shear viscosities by 3-4 orders of magnitude.