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首页> 外文期刊>Chemistry: A European journal >Lyotropic Liquid Crystal to Soft Mesocrystal Transformation in Hydrated Salt-Surfactant Mixtures
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Lyotropic Liquid Crystal to Soft Mesocrystal Transformation in Hydrated Salt-Surfactant Mixtures

机译：水合盐-表面活性剂混合物中的溶致液晶向软介晶转变

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摘要

Hydrated CaCl_2, LiI, and MgCl_2 salts induce self-assembly in nonionic surfactants (such as C_(12)H_(25)-(OCH_2CH_2)_(10)OH) 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 CaCl_2, LiI, and MgCl_2 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 MgCl_2 and smallest in the CaCl_2 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.
机译：水合的CaCl_2，LiI和MgCl_2盐在非离子表面活性剂（例如C_（12）H_（25）-（OCH_2CH_2）_（10）OH）中诱导自组装，形成经历相的溶致液晶（LLC）中间相在环境条件下转变为新型的软介晶（SMC）。可以通过老化LLC样品来获得SMC样品，这些LLC样品是通过将透明的均质水，盐和表面活性剂溶液旋涂，浸涂或滴铸在基板表面上而制成薄膜的。 LLC中间相在CaCl_2，LiI和MgCl_2中间相中分别以高达8、10和4的盐/表面活性剂摩尔比（分别对应于59、68和40 wt％的盐/表面活性剂）存在。 SMC相可以在较高的相对湿度下转变回LLC中间相。已经使用粉末X射线衍射（PXRD），偏振光学显微镜（POM）和FTIR技术监控了相变。 LLC中间相仅在小角度发生衍射，而SMC在小角度和宽角度均发生衍射。 LLC中间相的FTIR光谱中广泛的表面活性剂特征随着SMC的形成变得清晰并得到很好的分辨。中间相的晶胞在SMC转变时膨胀，其中MgCl_2中的膨胀最大，而CaCl_2系统中的膨胀最小。 SMC的POM图像显示具有清晰边缘的双折射纹理，类似于晶体。然而，晶体的表面像屈曲图案一样被高度图案化，这表明这些晶体非常柔软。这种不寻常的相行为可能有利于在相变材料和介孔结构材料领域设计新的软材料，并且证明了盐表面活性剂介相中相行为的丰富性。

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