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The role of counterions on the elasticity of highly charged lamellar phases: A small-angle x-ray and neutron-scattering determination

Abstract : The structure and fluctuations of the swollen Lα lamellar phase of highly charged surfactant didodecyldimethylammonium halide fluid bilayers (DDA+X−) are studied using high-resolution small-angle x-ray scattering and medium-resolution, high-contrast small-angle neutron-scattering. The Caillé parameter η, as a function of the swelling (Lα periodicity d), was determined from the full q-range fits of the measured scattering profiles for three different counterions (X−=Cl−, Br−, and NO−3). This parameter quantifies the amplitude of the membrane fluctuations within the Landau–de Gennes smectic-A linear elasticity theory. The different anions used gave strong specific effects at the maximum swelling of the Lα phase, while at lower swellings a two-phase coexistence of swollen and collapsed lamellae (d∼30 and ∼80Å) was observed for bromide and nitrate ions. Over the intermediate dilution range for all three counterions, a single Lα phase can be continuously swollen with pure water which is governed by an equation of state (i.e., osmotic pressure versus period) and thermally excited fluctuation amplitudes that can be well described by the same Poisson–Boltzmann calculation. The membranes were found to be slightly stiffer than predicted by purely electrostatic repulsions, and this is tentatively attributed to an extra bending rigidity contribution from the surfactant chains.
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https://hal-univ-lemans.archives-ouvertes.fr/hal-02538768
Contributeur : Guillaume Brotons <>
Soumis le : jeudi 9 avril 2020 - 16:15:38
Dernière modification le : samedi 11 avril 2020 - 01:17:54

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Guillaume Brotons, Monique Dubois, Luc Belloni, Isabelle Grillo, Theyencheri Narayanan, et al.. The role of counterions on the elasticity of highly charged lamellar phases: A small-angle x-ray and neutron-scattering determination. Journal of Chemical Physics, American Institute of Physics, 2005, 123 (2), pp.024704. ⟨10.1063/1.1950667⟩. ⟨hal-02538768⟩

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