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 language | English (US) |
|---|---|
| Pages (from-to) | 2290-2301 |
| Number of pages | 12 |
| Journal | Langmuir |
| Volume | 34 |
| Issue number | 6 |
| DOIs | |
| State | Published - Feb 13 2018 |
Bibliographical note
Funding Information:This work has been supported by National Science Foundation grant CHE-1608115. Synchrotron SAXS analyses were conducted at Sector 12 of the Advanced Photon Source (APS), a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract no. DE-AC02-06CH11357. Research reported in this publication was supported by the Office of the Director, National Institutes of Health under award number S10OD011952. This content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. We also thank Dr. Sung Kim, Dr. Tyler J. Mann and Grayson L. Jackson for helpful discussions.
Funding Information:
This work has been supported by National Science Foundation grant CHE-1608115. Synchrotron SAXS analyses were conducted at Sector 12 of the Advanced Photon Source (APS), a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract no. DE-AC02-06CH11357. Research reported in this publication was supported by the Office of the Director, National Institutes of Health under award number S10OD011952. This content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. We also thank Dr. Sung Kim, Dr. Tyler J. Mann, and Grayson L. Jackson for helpful discussions.
Publisher Copyright:
© 2018 American Chemical Society.