Counterion-Dependent Access to Low-Symmetry Lyotropic Sphere Packings of Ionic Surfactant Micelles
Counterion-Dependent Access to Low-Symmetry Lyotropic Sphere Packings of Ionic Surfactant Micelles
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DOI：
10.1021/acs.langmuir.7b03833
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发表时间：
2018-02-13
期刊：
影响因子：
3.9
通讯作者：
Mahanthappa, Mahesh K.
中科院分区：
文献类型：
--
作者：
Jayaraman, Ashish;Mahanthappa, Mahesh K.
研究了水驱动的同系双阴离子表面活性剂自组装成溶致液晶（LLCs）的过程，重点研究了表面活性剂的头基和反离子身份如何引导超分子球形中间相的选择。用变温小角X射线散射（SAXS）方法研究了两种烷基丙二酸盐表面活性剂（C（n）Mal-M-2）（n = 8（辛基）或10（癸基），M = Cs+或（CH_3）（4）N+）的胶束堆积结构。观察到的球形形态包括体心立方（BCC）、六方密堆积（HCP）和四面体密堆积（FK）AlS和α相（分别为Pm 3（-）n和P4（2）/mnm对称性）。此前仅在另一种最低水合表面活性剂中观察到，a相是一种罕见的LLC形态，包括含有30个亚2纳米准球形胶束的低对称性晶胞，每个胶束属于具有离散聚集数的五种对称等效类别之一。C（n）Mal M-2 LLC的温度-水浓度相图显示，σ相的形成敏感地取决于表面活性剂抗衡物的大小和极化率以及表面活性剂烷基尾的长度。这些意见是合理的全球包装对称性和局部粒子对称性之间的微妙的相互作用，以及在何种程度上counterheadgroup相关性执行后者的结构，在这些LLC阶段。
The water-driven self-assembly of homologous dianionic surfactants into lyotropic liquid crystals (LLCs) is investigated, with a focus on understanding how surfactant headgroup and counterion identities guide supramolecular spherical mesophase selection. Using temperature dependent small angle X-ray scattering (SAXS), we demonstrate that 2 alkylmalonate surfactants (C(n)Mal-M-2) with n = 8 (octyl) or 10 (decyl) and M = Cs+, or (CH3)(4)N+ form both simple and complex micelle packings. Observed spherical morphologies include body-centered cubic (BCC), hexagonally closest packed (HCP), and tetrahedrally closest-packed Frank-Kasper (FK) AlS and a phases (Pm3(-)n and P4(2)/mnm symmetries, respectively). Previously observed in only one other minimally hydrated surfactant, the a phase is a rare LLC morphology comprising a low symmetry unit cell containing 30 sub 2 nm quasispherical micelles, each of which belongs to one of five symmetry equivalent classes with discrete aggregation numbers. Temperature versus water concentration phase maps for C(n)Mal M-2 LLCs reveal that sigma-phase formation depends sensitively on the size and polarizability of the surfactant counterion and the length of the surfactant alkyl tail. These observations are rationalized in terms of a delicate interplay between global packing symmetry and local particle symmetry, and the extent to which counterion headgroup correlations enforce the latter structures in these LLC phases.