Transition from a Sponge-Like to an Onion-Like Nanostructure in the L3 Phase - Part I

Philipp Menold; Reinhard Strey; Stefan Roitsch; Natalie Preisig; Cosima Stubenrauch

doi:10.1016/j.jcis.2023.09.194

Transition from a Sponge-Like to an Onion-Like Nanostructure in the L₃ Phase - Part I

J Colloid Interface Sci. 2024 Jan;653(Pt B):1743-1752. doi: 10.1016/j.jcis.2023.09.194. Epub 2023 Oct 2.

Authors

Philipp Menold¹, Reinhard Strey², Stefan Roitsch², Natalie Preisig¹, Cosima Stubenrauch³

Affiliations

¹ Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany.
² Institute of Physical Chemistry, University of Cologne, Luxemburger Straße 116, 50939 Cologne, Germany.
³ Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany. Electronic address: cosima.stubenrauch@ipc.uni-stuttgart.de.

PMID: 37827012
DOI: 10.1016/j.jcis.2023.09.194

Abstract

Hypothesis: In the phase diagram of the system H₂O/NaCl - AOT (sodium bis(2-ethylhexyl) sulfosuccinate) a homogeneous L₃ channel can be detected at T = 25 °C as a function of the surfactant and the NaCl mass fraction. Our hypothesis is that a structural transition from a sponge-like to an onion-like structure occurs in this channel.

Experiments: We (a) determined the relevant part of the phase diagram, (b) carried out electrical conductivity and viscosity measurements, (c) visualized the nanostructure with freeze-fracture electron microscopy (FFEM) and freeze fracture direct imaging (FFDI), (d) determined the characteristic length scales from Small Angle Neutron Scattering (SANS) curves.

Findings: We detected a narrow one-phase L₃ channel in which the conductivities decrease, while the viscosities increase with increasing surfactant and salt mass fractions. Together with the FFEM/FFDI images and the SANS curves we provide experimental evidence for a structural transition from a sponge-like to an onion-like structure: all structures as well as their coexistences are thermodynamically stable.

Keywords: Transition between sponge-like and onion-like structures; onion-like structure of L(3) phases; structures in ternary system H(2)O/NaCl-AOT.