Effect of Cyclohexane on the Phase Behavior of L64/1-Butyl-3-Methylimidazolium Tetrafluoroborate System

The triblock copolymer poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (L64, PEO₁₃PPO₃₀PEO₁₃) in 1-butyl-3-methylimidazolium tetrafluoroborate (Bmim]BF₄]) can form lamellar liquid crystalline (L_α). The effect of apolar cyclohexane molecules on the L_α phase was investigated by using polarized optical microscopy (POM) and small-angle x-ray scattering (SAXS). The results of POM and SAXS show that a suitable amount of cyclohexane can contribute to the formation of lamellar liquid crystals, and the ordering of L_α phase is increased. For comparison, the effect of polar water on L_α phase was explored. After adding water, both EO groups and BF₄]^– anion can form hydrogen bonds with water molecules, which weakens the electrostatic interactions between L64 and Bmim]BF₄] and therefore the ordering of lamellar structures is destroyed.