Gozde Barim - Lyotropic Liquid Crystal to Soft Mesocrystal Transformation in Hydrated Salt–Surfactant Mixtures

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  Publication Details (including relevant citation   information):

    Dr. Cemal Albayrak,

    Gözde Barım,

    Prof. Ömer Dag

  Article first   published online: 17 SEP 2013


    Hydrated CaCl2,   LiI, and MgCl2    salts induce self-assembly in nonionic surfactants (such as   C12H25(OCH2CH2)10OH)   to form lyotropic liquid-crystalline (LLC) mesophases that   undergo a phase transition to a new type of soft mesocrystal   (SMC) under ambient conditions. The SMC samples can be obtained   by aging the LLC samples, which were prepared as thin films by   spin-coating, dip-coating, or drop-casting of a clear homogenized   solution of water, salt, and surfactant over a substrate surface.   The LLC mesophase exists up to a salt/surfactant mole ratio of 8,   10, and 4 (corresponding to 59, 68, and 40 wt % salt/surfactant)   in the CaCl2,   LiI, and MgCl2    mesophases, respectively. The SMC phase can transform back to a   LLC mesophase at a higher relative humidity. The phase   transformations have been monitored using powder X-ray   diffraction (PXRD), polarized optical microscopy (POM), and FTIR   techniques. The LLC mesophases only diffract at small angles, but   the SMCs diffract at both small and wide angles. The broad   surfactant features in the FTIR spectra of the LLC mesophases   become sharp and well resolved upon SMC formation. The unit cell   of the mesophases expands upon SMC transformation, in which the   expansion is largest in the MgCl2    and smallest in the CaCl2    systems. The POM images of the SMCs display birefringent textures   with well-defined edges, similar to crystals. However, the   surface of the crystals is highly patterned, like buckling   patterns, which indicates that these crystals are quite soft.   This unusual phase behavior could be beneficial in designing new   soft materials in the fields of phase-changing materials and   mesostructured materials, and it demonstrates the richness of the   phase behavior in the salt–surfactant mesophases.

  Address (URL): http://onlinelibrary.wiley.com/doi/10.1002/chem.201301662/abstract;jsessionid=80 5DF452E86EE4088A6E8F492F7797F8.f02t03