Issue 31, 2013
From the journal:

Soft Matter

Dynamic flow behaviour of surfactant vesicles under shear flow: role of a multilamellar microstructure

Angelo Pommella,*ab   Sergio Casertaabc  and  Stefano Guidoabc  

* Corresponding authors

a Dipartimento di Ingegneria Chimica, dei Materiali e della Produzione Industriale, Università di Napoli Federico II, 80125 Napoli, Italy
E-mail: angelo.pommella@gmail.com
Fax: +39 0812391800
Tel: +39 0817682261

b CEINGE Advanced Biotechnologies, 80145 Napoli, Italy

c Dipartimento di Ingegneria Chimica, dei Materiali e della Produzione Industriale, Università di Napoli Federico II, UdR INSTM, P.le Tecchio, 80, Napoli, Italy

Abstract

Surfactant based systems are ubiquitous in everyday life products, including food, pharmaceuticals, and detergents. In concentrated solutions, surfactants may assemble into multilamellar, onion-like vesicles, whose size distribution is known to be affected by the action of flow during processing and usage. However, very little is known about the dynamic behaviour and the mechanisms by which the packed microstructure of a surfactant multilamellar vesicle (MLV) is deformed under flow. In this work, the microstructure of surfactant MLVs is investigated both at rest by confocal microscopy and under flow by a rheo-optical parallel plate apparatus using bright field and polarized light microscopy. Small MLVs have a more homogeneous multilamellar structure extending to the vesicle centre and show small deformation regimes, such as tumbling and breathing. Larger MLVs have an inner isotropic core surrounded by a multilamellar shell and can also exhibit a tank-treading deformation mode depending on the flow conditions. The main result of this work is that tank-treading is associated with the formation of parabolic focal conic defects in the outer shell, which is driven by shear-induced bilayer dilation and undulation as in smectic A liquid crystals, and with convection-induced surfactant re-arrangement at a constant shell volume. This finding is supported by the analysis of vesicle retraction upon cessation of flow, which scales with the inverse third power of radius and thus is consistent with the effect of a compressibility modulus.

Graphical abstract: Dynamic flow behaviour of surfactant vesicles under shear flow: role of a multilamellar microstructure

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Article information

DOI
https://doi.org/10.1039/C3SM50617G
Article type
Paper
Submitted
28 Feb 2013
Accepted
31 May 2013
First published
31 May 2013

Soft Matter, 2013,9, 7545-7552

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Dynamic flow behaviour of surfactant vesicles under shear flow: role of a multilamellar microstructure

A. Pommella, S. Caserta and S. Guido, Soft Matter, 2013, 9, 7545 DOI: 10.1039/C3SM50617G

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