Complex Fluids and Polymer Engineering, National Chemical Laboratory, Pune 411008, India.
Langmuir. 2011 Aug 16;27(16):9792-800. doi: 10.1021/la201767p. Epub 2011 Jul 25.
We have investigated the microstructure and phase behavior of monoglyceride-based lyotropic liquid crystals in the presence of hydrophilic silica colloidal particles of size comparable to or slightly exceeding the repeat units of the different liquid crystalline phases. Using small angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC), we compare the structural properties of the neat mesophases with those of the systems containing silica colloidal particles. It is found that the colloidal particles always macrophase separate in inverse bicontinuous cubic phases of gyroid (Ia3d) and double diamond (Pn3m) symmetries. SAXS data for the inverse columnar hexagonal phase (H(II)) and lamellar phase (L(α)) suggest that a low volume fraction of the nanoparticles can be accommodated within the mesophases, but that at concentrations above a given threshold, the particles do macrophase separate also in these systems. The behavior is interpreted in terms of the enthalpic and entropic interactions of the nanoparticles with the lamellar and hexagonal phases, and we propose that, in the low concentration limit, the nanoparticles are acting as point defects within the mesophases and, upon further increase in concentration, initiate nucleation of nanoparticles clusters, leading to a macroscopic phase separation.
我们研究了单甘油脂基溶致液晶在亲水性二氧化硅胶体颗粒存在下的微观结构和相行为，这些胶体颗粒的尺寸与不同液晶相的重复单元相当或略大于重复单元。我们使用小角 X 射线散射（SAXS）和差示扫描量热法（DSC）比较了纯中间相和含有二氧化硅胶体颗粒的体系的结构性质。结果发现，胶体颗粒总是在具有回旋体（Ia3d）和双菱形（Pn3m）对称性的反向双连续立方相（I a3d）和双菱形（Pn3m）相中宏观分离。对于反向柱状六方相（H（II））和层状相（L（α））的 SAXS 数据表明，在纳米颗粒的低体积分数下，它们可以容纳在中间相中，但在高于给定阈值的浓度下，颗粒也会在这些体系中宏观分离。这种行为是根据纳米颗粒与层状相和六方相的焓和熵相互作用来解释的，我们提出，在低浓度极限下，纳米颗粒在中间相内充当点缺陷，并且随着浓度的进一步增加，引发纳米颗粒簇的成核，导致宏观相分离。
