Acta Phys. -Chim. Sin. ›› 2012, Vol. 28 ›› Issue (06): 1411-1417.doi: 10.3866/PKU.WHXB201203262

• SOFT MATTER • Previous Articles     Next Articles

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

ZHAO Xue-Yan1, CAO Yu-Rong2, CAO Gui-Rong1, XIAO Rui-Jie1   

  1. 1. Department of Fundamental Courses, Institute of Disaster Prevention, Langfang 065201, Hebei Province, P. R. China;
    2. Department of Information, China Cleaning Industry Association, Beijing 100044, P. R. China
  • Received:2012-02-07 Revised:2012-03-23 Published:2012-05-17
  • Contact: ZHAO Xue-Yan
  • Supported by:

    The project was supported by the Teachers' Scientific Research Fund of China Earthquake Administration (20110123) and Fundamental Research Funds for the Central Universities for Innovative Research Team, China (ZY20110103).

Abstract: 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-3- methylimidazolium 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.

Key words: Ionic liquid, Block copolymer, Lamellar liquid crystalline, Aggregation behavior, Formation mechanism