Light-responsive multillamellar vesicles in coumaric acid/alkyldimethylamine oxide binary systems: Effects of surfactant and hydrotrope structures

Herein, we report a series of novel light-responsive multilamellar vesicles based on the surfactantihydrotrope binary systems. The phase behaviors of alkyldimethylamine oxide (C(m)DOMA, m = 10, 12, 14) and trans-coumaric acid (trans-CA) isomerides, including trans-ortho-coumaric acid (trans-OCA), trans-meta-coumaric acid (trans-MCA) and trans-para-coumaric acid (trans-PCA), show that the multilamellar vesicle (MLV) formation region is commonly presented in the trans-CA/C(m)DMAO systems except trans-PCA/C(12)DMAO. Moreover, the molecular structures of C(m)DMAO and trans-CA affect the multilamellar vesicle formation region significantly. Generally speaking, the bigger the m, the larger the MLV region. Various techniques such as rheology, polarized optical microscopy (POM), H-1 NMR, H-2 NMR, cryogen transmission electron microscopy (cryo-TEM) and freeze-fracture transmission electron microscopy (FF-TEM) are used to characterize the aggregate structures. The multilamellar vesicles can transform into a homogeneous and transparent micelle phase or a two-phase system in the trans-OCA/C(m)DMAO binary systems under UV light irradiation, which depends on the chain length of C(m)DMAO and the molar ratio of [trans-OCA]/[C(m)DMAO]. Specifically, the light-stimuli response of multilamellar vesicles in the trans-OCA/C(12)DMAO system is representatively studied in detail. UV-vis spectra and H-1 NMR measurements illustrate that the light-induced trans-OCA to cis-OCA isomerization is essential during the transitions and the light induced two-phase formation is attributed to the enrichment of surfactants, because the trans-cis isomerization can not only strengthen the hydrophilicity of cis-OCA but also increase the steric hindrance between cis-OCA and C(12)DMAO, and thereby altering the morphology of aggregate and the rheological response of bulk phase significantly. (C) 2016 Elsevier Inc. All rights reserved.