Cao Yu, Alaasar Mohamed, Zhang Lei, Zhu Chenhui, Tschierske Carsten, Liu Feng
Shaanxi International Research Center for Soft Matter, State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049, P. R. China.
MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, School of Physics, Xi'an Jiaotong University, Xi'an 710049, China.
J Am Chem Soc. 2022 Apr 20;144(15):6936-6945. doi: 10.1021/jacs.2c01511. Epub 2022 Apr 8.
Bicontinuous and multicontinuous network phases are among nature's most complex structures in soft matter systems. Here, a chiral bicontinuous tetragonal phase is reported as a new stable liquid crystalline intermediate phase at the transition between two cubic phases, the achiral double gyroid and the chiral triple network cubic phase with an 23 space group, both formed by dynamic networks of helices. The mirror symmetry of the double gyroid, representing a -structure of two enantiomorphic networks, is broken at the transition to this tetragonal phase by retaining uniform helicity only along one network while losing it along the other one. This leads to a conglomerate of enantiomorphic tetragonal space groups, 422 and 422. Phase structures and chirality were analyzed by small-angle X-ray scattering (SAXS), grazing-incidence small-angle X-ray scattering (GISAXS), resonant soft X-ray scattering (RSoXS) at the carbon K-edge, and model-dependent SAXS/RSoXS simulation. Our findings not only lead to a new bicontinuous network-type three-dimensional mesophase but also reveal a mechanism of mirror symmetry breaking in soft matter by partial -structure racemization at the transition from enantiophilic to enantiophobic interhelical self-assembly.
双连续和多连续网络相是软物质系统中自然界最复杂的结构之一。在此，报道了一种手性双连续四方相，它是在两种立方相（非手性双螺旋体和具有23空间群的手性三重网络立方相，两者均由螺旋动态网络形成）之间的转变过程中出现的一种新的稳定液晶中间相。双螺旋体的镜像对称性代表了两个对映体网络的结构，在向该四方相转变时被打破，因为仅沿着一个网络保持均匀螺旋度，而沿着另一个网络失去螺旋度。这导致了对映体四方空间群422和422的聚集体。通过小角X射线散射（SAXS）、掠入射小角X射线散射（GISAXS）、碳K边的共振软X射线散射（RSoXS）以及基于模型的SAXS/RSoXS模拟对相结构和手性进行了分析。我们的发现不仅导致了一种新的双连续网络型三维中间相，还揭示了在从亲对映体到憎对映体的螺旋间自组装转变过程中，通过部分结构外消旋作用实现软物质中镜像对称性破缺的机制。
