Micellar Mimicry of Intermetallic C14 and C15 Laves Phases by Aqueous Lyotropic Self-Assembly

• Published in: ACS nano 2018-04, Vol.12 (4), p.3226-3234
• Main Authors: Baez-Cotto, Carlos M, Mahanthappa, Mahesh K
• Format: Article
• Language: English
• Subjects: Frank−Kasper phases; Group theory; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Lattices; liquid crystals; lyotropic phase; Micelles; self-assembly; superlattices; Surfactants; X-ray scattering
• ISSN: 1936-0851; 1936-086X
• DOI: 10.1021/acsnano.7b07475

Concentration-dependent supramolecular self-assembly of amphiphilic molecules in water furnishes a variety of nanostructured lyotropic liquid crystals (LLCs), which typically display high symmetry bicontinuous network and discontinuous micellar morphologies. Aqueous dispersions of soft spherical micelles derived from small molecule amphiphile hydration typically pack into exemplary body-centered cubic and closest-packed LLCs. However, investigations of hydrated mixtures of the ionic surfactant tetramethylammonium decanoate loaded with 40 wt % n-decane (TMADec-40) revealed the formation of a high symmetry bicontinuous double diamond LLC, as well as cubic C15 and hexagonal C14 Laves LLC phases that mirror the MgCu2 and MgZn2 intermetallic structure types, respectively. Detailed small-angle X-ray scattering analyses demonstrate that the complex C15 and C14 LLCs exhibit large unit cells, in which 12 or more ∼3–4 nm diameter micelles of multiple discrete sizes arrange into tetrahedral close packing arrangements with exceptional long-range translational order. The symmetry breaking that drives self-assembly into these low-symmetry LLC phases is rationalized in terms of a frustrated balance between maximizing counterion-mediated micellar cohesion within the ensemble of oil-swollen particles, while simultaneously optimizing local spherical particle symmetry to minimize molecular-level variations in surfactant solvation.