title: Columnar molecular aggregation in the aqueous solutions of disodium cromoglycate.
abstract: Stack, chimneylike, and threadlike assemblies have previously been proposed for the structure of disodium cromoglycate (DSCG) aggregates in aqueous solutions. The results of the synchrotron x-ray scattering investigations reported here reveal the formation of simple columnar assemblies with π-π stacking at a separation of 3.4 Å between the DSCG molecules. Lateral separation between the assemblies is concentration and temperature dependent, varying from ∼35 to 42 Å in the orientationally ordered nematic (N) phase and from 27 to 32 Å in the columnar or middle (M) phase having long range lateral positional order. The assemblies' length depends on concentration and consists of ∼23 molecules in the N phase, becoming three to ten times larger in the M phase. The scission energy is concentration dependent in the N phase with values ∼7.19 ± 0.14 k_{B}T (15 wt %), 2.73 ± 0.4 k_{B}T (20 wt %), and 3.05 ± 0.2 k_{B}T (25 wt %). Solutions of all concentrations undergo a spinodal decomposition at temperatures above ∼40 °C, resulting in DSCG-rich regions with the M phase and water-rich regions in the N and isotropic phases.
authors.affiliation: Department of Physics, Kent State University, Kent, Ohio 44242, USA.
authors.forename: Dena M
authors.initials: DM
authors.lastname: Agra-Kooijman
authors.affiliation: Department of Physics, Kent State University, Kent, Ohio 44242, USA.
authors.forename: Gautam
authors.initials: G
authors.lastname: Singh
authors.affiliation: Department of Chemistry, Berlin Institute of Technology, Strasse des 17. Juni 124, 10623 Berlin, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Lorenz
authors.affiliation: Department of Physics & Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081, USA.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Collings
authors.affiliation: Department of Chemistry, University of Paderborn, Warburger Strasse 100, 33098 Paderborn, Germany.
authors.forename: Heinz-S
authors.initials: HS
authors.lastname: Kitzerow
authors.affiliation: Department of Physics, Kent State University, Kent, Ohio 44242, USA.
authors.forename: Satyendra
authors.initials: S
authors.lastname: Kumar
mesh_terms: D004205:Cromolyn Sodium / Q000737:chemistry*; D003460:Crystallization / Q000379:methods*; D046911:Macromolecular Substances / Q000737:chemistry; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D044367:Phase Transition; D012996:Solutions / Q000737:chemistry; D014867:Water / Q000737:chemistry*
chemical_list: D046911:Macromolecular Substances; D012996:Solutions; D014867:Water; D004205:Cromolyn Sodium