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.

Effects of a Spacer on the Phase Behavior of Gemini Surfactants in Ethanolammonium Nitrate

“…A broad interaction peak appeared at medium q , and I ( q ) decreased with the oscillation at high q . These characteristics indicated the formation of micelles . On the other hand, the I ( q ) curve of LP was rather weak, indicating no sign of micelles.…”

“…The sample at C 12‑2‑12 = 20% was taken as an example for further characterizations. 1 H NMR was employed to determine the composition of the two phases, with the results shown in Figure S2 . It was found that the amount of 12-2-12 in UP was around 41% of the total UP weight whereas there was little in LP.…”

Aggregation Behavior of Pyrrolidinium Ionic Liquid Surfactants in −OH-Functionalized Ammonium-Based Protic Ionic Liquids

“…The standard Gibbs free energy change and enthalpy and entropy changes (Δ G m 0 , Δ H m 0 , and Δ S m 0 ) for the aggregation process have been determined by the following equations: ,, Here, x cmc is the cmc expressed in mole fraction. The n = 1, because the high ion environment in PILs completely neutralizes the charge of the surfactant head groups. ,,, …”

“…The n = 1, because the high ion environment in PILs completely neutralizes the charge of the surfactant head groups. 6,25,38,39 The as-obtained thermodynamic parameters for the aggregation process are given in Tables 7−9. As can be seen from these tables, all the ΔG m 0 values were negative, suggesting that the aggregation of the surfactants in PILs was a favorable process.…”

Self‐Assembly of Anionic Gemini‐Surfactant‐Assisted Fabrication of Copper Oxide Nanostructures

“…The tendency of the hydrophobic tails aggregating in aqueous solution is the driving force for spherical micelles formation, which is spontaneously the primary self‐assembly behavior of surfactant. While the hydroxyls on the hydrophilic head groups display the active functional groups for hydrogen bonds formation and for secondary self‐assembly ,. According to Figure , the self‐assembly of C 12 ‐Ar‐C 12 leads to the formation of threadlike micelles, which is structurally similar to cylindrical micelles, in which the hydrophobic tails pack in the core of the micelles while the hydrophilic moieties displayed on the surface.…”