Prehm Marko, Cheng Xiao Hong, Diele Siegmar, Das Malay Kumar, Tschierske Carsten
Martin Luther University Halle-Wittenberg, Institute of Organic Chemistry, Kurt-Mothes Strasse 2, D-06120 Halle, Germany.
J Am Chem Soc. 2002 Oct 16;124(41):12072-3. doi: 10.1021/ja027869x.
Novel lamellar mesophases which are quite distinct from conventional smectic mesophases were obtained with a bolaamphiphilic triblock molecule composed of a rigid biphenyl core, two polar 2,3-dihydroxypropoxy groups in the terminal 4- and 4'-positions, and a semiperfluorinated chain [O(CH2)6C10F21] in the lateral 3-position. The competitive combination of microsegregation and rigidity in this molecule leads to layer structures in which the bolaamphiphilic cores segregate from the lateral chains into distinct sublayers. In these sublayers the biphenyl cores are aligned parallel to the layer planes. Decreasing the temperature leads to a subsequent inset of orientational and positional order of the biphenyl unit, which leads to a transition from an uniaxial SmA phase to a biaxial SmAb phase and finally to a mesophase with an additional periodicity within the aromatic sublayers. Here, microsegregation occurs on two distinct levels: The segregation of the nonpolar chains from the aromatic cores leads to the "bulk" layer structure and segregation of polar and aromatic subunits within the aromatic sublayers gives rise to an additional periodicity within the aromatic sublayers. These phases can be regarded as smectic phases built up by quasi-2D layers with nematic, respectively SmA-like order, separated by isotropic layers of the lateral chains.
通过一种由刚性联苯核心、末端4-和4'-位的两个极性2,3-二羟基丙氧基以及3-位的侧向半全氟链[O(CH2)6C10F21]组成的双极性两亲三嵌段分子，获得了与传统近晶相截然不同的新型层状中间相。该分子中微相分离和刚性的竞争组合导致形成层状结构，其中双极性两亲核心从侧向链中分离成不同的子层。在这些子层中，联苯核心与层平面平行排列。降低温度会导致联苯单元随后出现取向和位置有序，这会导致从单轴SmA相转变为双轴SmAb相，最终转变为在芳香族子层内具有额外周期性的中间相。在此，微相分离发生在两个不同层面：非极性链与芳香族核心的分离导致“主体”层状结构，而芳香族子层内极性和芳香族亚基的分离在芳香族子层内产生额外的周期性。这些相可被视为由具有向列相或类似SmA序的准二维层构建的近晶相，由侧向链的各向同性层分隔。
