Issue 37, 2022

Effect of salt on the lamellar Lα-to-MLV transformation in SDS/octanol/water under microfluidic flow

Abstract

We investigate the effect of added (NaCl) salt and varying flow rate on the phase behaviour and flow response of a model surfactant Lα phase, sodium dodecyl sulfate (SDS)/octanol/water, using small angle neutron scattering (SANS) and polarised optical microscopy in microfluidics, supported by NMR, viscosity, conductivity and zeta potential measurements. A long (∼3 m) tubular microchannel device is employed to quantify the spatiotemporal structural evolution of the system towards multilamellar vesicles (MLV). The effect of salt is rationalised in terms of changes in membrane bending rigidity and phase stability. It is shown that ∼1.8 w/w% NaCl addition results in MLV formation within the shortest time (or equivalent lengthscale) and yields near-centrosymmetric scattering profiles characteristic of MLVs (at a reference 1 mL h−1 flow rate and ≃90 s−1 shear rate). Further salt addition yields biphasic systems that remain strongly aligned under flow, while lower salt content also increases scattering anisotropy, accompanied by higher membrane rigidity and solution viscosity. Increasing flow rate causes greater initial Lα alignment, and thus flow anisotropy, but also faster evolution towards isotropy and MLV formation.

Graphical abstract: Effect of salt on the lamellar Lα-to-MLV transformation in SDS/octanol/water under microfluidic flow

Supplementary files

Article information

Article type
Paper
Submitted
17 May 2022
Accepted
23 Jul 2022
First published
25 Jul 2022
This article is Open Access
Creative Commons BY license

Soft Matter, 2022,18, 7010-7019

Effect of salt on the lamellar Lα-to-MLV transformation in SDS/octanol/water under microfluidic flow

L. Donina, L. Porcar and J. T. Cabral, Soft Matter, 2022, 18, 7010 DOI: 10.1039/D2SM00643J

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