Counterion-Dependent Access to Low-Symmetry Lyotropic Sphere Packings of Ionic Surfactant Micelles

Ashish Jayaraman, Mahesh Mahanthappa

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

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 (CnMal-M2) with n = 8 (octyl) or 10 (decyl) and M = K+, Cs+, or (CH3)4N+ 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) A15 and σ phases (Pm3(-)n and P42/mnm symmetries, respectively). Previously observed in only one other minimally hydrated surfactant, the σ 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 CnMal-M2 LLCs reveal that σ-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.

Original languageEnglish (US)
Pages (from-to)2290-2301
Number of pages12
JournalLangmuir
Volume34
Issue number6
DOIs
StatePublished - Feb 13 2018

Fingerprint

Micelles
Surface-Active Agents
Liquid Crystals
micelles
Surface active agents
surfactants
Liquid crystals
symmetry
liquid crystals
crystal morphology
water temperature
Water
Crystal symmetry
X ray scattering
Self assembly
self assembly
Agglomeration
Temperature
cells
scattering

PubMed: MeSH publication types

  • Journal Article
  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

Cite this

Counterion-Dependent Access to Low-Symmetry Lyotropic Sphere Packings of Ionic Surfactant Micelles. / Jayaraman, Ashish; Mahanthappa, Mahesh.

In: Langmuir, Vol. 34, No. 6, 13.02.2018, p. 2290-2301.

Research output: Contribution to journalArticle

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