嵌段共聚物L64在1-丁基-3-甲基咪唑四氟硼酸盐离子液体中形成的层状液晶

利用偏光显微镜(POM)、小角X射线散射(SAXS)及傅里叶变换红外(FTIR)光谱技术研究了嵌段共聚物PluronicL64(PEO13PPO30PEO13)(PEO:聚氧乙烯;PPO:聚氧丙烯)在室温离子液体1-丁基-3-甲基咪唑四氟硼酸盐[Bmim][BF4]中的聚集行为.绘制了L64/[Bmim][BF4]体系的相图,当L64浓度介于40%-65%(w,质量分数)之间时,L64可与[Bmim][BF4]形成层状液晶.SAXS结果表明,液晶层间距随L64浓度的增加而降低.温度对液晶微结构影响较大,液晶层间距随温度的升高而增大,极性头截面积则减小.并且,在一定温度范围内,升温可使体系的有序性增强.但是,随温度的进一步升高,[Bmim][BF4]与PEO链段之间的氢键被破坏,双折射现象消失,液晶有序性降低.此外,分析了层状液晶的形成机理,[Bmim][BF4]与L64分子间的氢键作用力、静电作用力以及疏溶剂力是液晶形成的驱动力.

Lamellar Liquid Crystalline Phase Formed by Triblock Copolymer L64 in 1-Butyl-3-methylimidazolium Tetrafluoroborate Ionic Liquid

The aggregation behavior of the triblock copolymer poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)(L64,PEO13PPO30PEO13) in the room-temperature ionic liquid 1-butyl-3methylimidazolium tetrafluoroborate([Bmim] [BF4]) was investigated using polarized optical microscopy(POM),small-angle X-ray scattering(SAXS),and Fourier transform infrared(FTIR) spectroscopy.The phase diagram of the L64/[Bmim][BF4] system is described,where the micellar phase(L1),a mixture of lamellar liquid crystalline(Lα) and L1 phases,the Lα phase,a mixture of Lα and reverse micellar(L2) phases,and the L2 phase are sequentially mapped.Among these phases,the behavior of the Lα phase formed in the L64/[Bmim][BF4] system in the L64 concentration region of 40%-65%(w,mass fraction) was focused on because it forms highly-ordered structures.The Maltese cross texture was found through POM characterization,and was typical for the Lα phase.The SAXS patterns further confirm the formation of the Lα phase.In addition,the lattice spacings of the Lα phase were obtained from the SAXS patterns.The effect of temperature on the microstructure of the Lα phase was also elucidated.As the temperature was increased,the lattice spacing and ordering of the Lα phase increased,while the interfacial area decreased for a certain temperature range.However,the birefringence of the Lα phase disappeared when the temperature reached a certain level,which was attributed to the breakdown of hydrogen bonding between [Bmim] [BF4] and poly(ethylene oxide) chains,so the ordering of the Lα phase was decreased.The formation mechanism of the Lα phase is also discussed.Hydrogen bonding,electrostatic and solvophobic interactions are believed to be the main driving forces for the formation of Lα phase in the L64/[Bmim][BF4] system.