Role of Water in the Lyotropic Liquid Crystalline Mesophase of Lithium Salts and Non-ionic Surfactants

Abstract

The lyotropic liquid crystalline (LLC) mesophase forms upon evaporation of water from aqueous solutions of LiX salts (X is Cl − , Br − , NO 3 − , or SCN − ) and a surfactant [C 12 H 25 (OCH 2 CH 2 ) 10 OH, abbreviated as C 12 E 10 ]. The LiX/ C 12 E 10 /H 2 O aqueous solutions have been monitored (during evaporation of their excess water to obtain stable LLC mesophases) by gravimetric, spectroscopic, and conductivity measurements to elucidate the role of water in these mesophases. The water/salt molar ratio in stable mesophases changes from 1.5 to 8.0, depending on the counteranion of the salt and the ambient humidity of the laboratory. The LiX/C 12 E 10 /H 2 O LLC mesophases lose water at lower humidity levels and absorb water at higher humidity levels. The LiCl-containing mesophase holds as few as four structural water molecules per LiCl, whereas the LiNO 3 mesophase holds 1.5 waters per salt (least among those assessed). This ratio strongly depends on the atmospheric humidity level; the water/LiX mole ratio increases by 0.08 ± 0.01 H 2 O in the LLC mesophases per percent humidity unit. Surprisingly, the LLC mesophases are stable (no salt leaching) in broad humidity (10−85%) and salt/surfactant mole ratio (2−10 LiX/C 12 E 10 ) ranges. Attenuated total reflectance Fourier transform infrared spectroscopic data show that the water molecules in the mesophase interact with salt species more strongly in the LiCl mesophase and more weakly in the case of the nitrate ion, which is evident by the shift of the O−H stretching band of water. The O−H stretching peak position in the mesophases decreases in the order ν LiCl > ν LiBr > ν LiSCN > ν LiNO 3 and accords well with the H 2 O/LiX mole ratio. The conductivity of the LLC mesophase also responds to the amount of water as well as the nature of the counteranion (X − ). The conductivity decreases in the order σ LiCl > σ LiBr > σ LiNO 3 > σ LiSCN at low salt mole ratios and in the order σ LiBr > σ LiCl > σ LiNO 3 > σ LiSCN at higher ratios due to structural changes in the mesophase.

Understanding specific ion effects and the Hofmeister series

“…351 The fact that mixed salt effects have also been studied in polyelectrolytes 352,353 and neutral polymer solutions (Section 5) presents alternative opportunities for studying SIEs via ionic surfactants, which are already known to influence mesophase behaviour in mixed salt-surfactant systems in an ion-specific way. 354,355 Ionic surfactants also enable systematic investigation and manipulation of SIEs, for instance by using a constant charge group with increasing aliphatic tail length ( i.e. in order to maintain a constant Coulombic interaction between the surfactant and the solvent, while varying non-Coulombic effects).…”

Nanoarchitectonics of Mesoporous M2P2O7 (M = Mn(II), Co(II), and Ni(II)) and M2–xCoxP2O7 and Transformation to Their Metal Hydroxides with Decent Charge Capacity in Alkali Media

“…Most of the volatile species (water and nitrate) are removed in 3 h, and the evaporation is almost complete in 24 h of aging under ambient condition. The weight versus time plot is quite different in the [M­(H 2 O) 6 ]­(NO 3 ) 2 /PPA/P123 system compared to a salt–surfactant system that forms a stable molten salt mediated LLC mesophase; this is likely due to an additional nitrate decomposition in the presence of PPA (see later). The final composition after the complete evaporation process is M 2 H x P 2 O 7 (NO 3 ) x · n H 2 O (where M is any of the above transition metal ions and x and n are nitrate/M (0.2–0.35) and water/M (3.0–1.8) mole ratios, respectively) under ambient conditions and depends on humidity (see latter).…”

Light-Induced Synthesis of Single-Crystalline Gold Microplates in an Open System

“…In fact, the LLC phase loses water at lower humidity levels and absorbs water at higher humidity levels. The LLC phase takes and gives water reversibly during its exposure to ambient conditions depending on the humidity of the environment, and the LLC phase is indeed stable (no leaching out salts) in a broad humidity level (10–85%) . Therefore, during the photochemical reaction, both matter (water) and energy (light or heat) can be exchanged with the environment.…”

“…The LLC phase takes and gives water reversibly during its exposure to ambient conditions depending on the humidity of the environment, and the LLC phase is indeed stable (no leaching out salts) in a broad humidity level (10−85%). 25 Therefore, during the photochemical reaction, both matter (water) and energy (light or heat) can be exchanged with the environment. Therefore, the LLC mesophase used in this study is an open system.…”