title: Core Freezing and Size Segregation in Surfactant Core-Shell Micelles.
abstract: Nonionic surfactants containing poly(ethylene oxide) are chemically simple and biocompatible and form core-shell micelles at a wide range of conditions. For those reasons, they and their aggregates have been widely investigated. Recently, irregularities that were observed in the low-temperature behavior of surfactants of the kind [CH3(CH2)(n)O(CH2CH2O)(m)H], (abbreviated CnEm) were assigned to a freezing-melting phase transition in the micellar core. In this work we expand the focus from the case of single component systems to binary surfactant systems at temperatures between 1 and 15 °C. By applying small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), and density measurements in pure C18E20 and C18E100 solutions and their mixtures, we show that core freezing/melting is also present in mixtures. Additionally, comparing SAXS data obtained from the mixture with those from the single components, it was possible to demonstrate that the phase transition leads to a reversible segregation of the surfactants from mixed micelles to distinct kinds of micelles of the two components.
authors.affiliation: †Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, 8000 Aarhus C, Denmark.
authors.forename: Beatrice
authors.initials: B
authors.lastname: Plazzotta
authors.affiliation: ‡Division of Applied Physical Chemistry, Department of Chemistry, KTH Royal Institute of Technology, Teknikringen 36, S-10044 Stockholm, Sweden.
authors.forename: Jing
authors.initials: J
authors.lastname: Dai
authors.affiliation: †Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, 8000 Aarhus C, Denmark.
authors.forename: Manja A
authors.initials: MA
authors.lastname: Behrens
authors.affiliation: ‡Division of Applied Physical Chemistry, Department of Chemistry, KTH Royal Institute of Technology, Teknikringen 36, S-10044 Stockholm, Sweden.
authors.forename: István
authors.initials: I
authors.lastname: Furó
authors.affiliation: †Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, 8000 Aarhus C, Denmark.
authors.forename: Jan Skov
authors.initials: JS
authors.lastname: Pedersen