title: Unique Phase Behaviors in the Gemini Surfactant/EAN Binary System: The Role of the Hydroxyl Group.
abstract: The hydroxyl group in the spacer of a cationic Gemini surfactant (12-3OH-12) caused dramatic changes of the phase behaviors in a protic ionic liquid (EAN). Here, the effects of the hydroxyl group on micellization and lyotropic liquid crystal formation were investigated through the surface tension, small-angle X-ray scattering, polarized optical microscopy, and rheological measurements. With the hydroxyl group in the spacer, the critical micellization concentration of 12-3OH-12 was found to be lower than that of the homologue without hydroxyl (12-3-12) and the 12-3OH-12 molecules packed more densely at the air/EAN interface. It was then interesting to observe a coexistence of two separated phases at wide concentration and temperature ranges in this 12-3OH-12/EAN system. Such a micellar phase separation was rarely observed in the ionic surfactant binary system. With the increase of surfactant concentration, the reverse hexagonal and bicontinuous cubic phases appeared in sequence, whereas only a reverse hexagonal phase was found in 12-3-12/EAN system. But, the hexagonal phases formed with 12-3OH-12 exhibited lower viscoelasticity and thermostability than those observed in 12-3-12/EAN system. Such unique changes in phase behaviors of 12-3OH-12 were ascribed to their enhanced solvophilic interactions of 12-3OH-12 and relatively weak solvophobic interactions in EAN.
authors.affiliation: Key Laboratory of Colloid and Interface Chemistry, Shandong University, Ministry of Education , Jinan, 250100, China.
authors.forename: Qintang
authors.initials: Q
authors.lastname: Li
authors.affiliation: Drilling Engineering and Technology Company, Shengli Petroleum Engineering Corporation Limited of SINOPEC , Dongying, 257064, China.
authors.forename: Xudong
authors.initials: X
authors.lastname: Wang
authors.forename: Xiu
authors.initials: X
authors.lastname: Yue
authors.affiliation: Key Laboratory of Colloid and Interface Chemistry, Shandong University, Ministry of Education , Jinan, 250100, China.
authors.forename: Xiao
authors.initials: X
authors.lastname: Chen