Distortion of surfactant lamellar phases induced by surface roughness
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https://doi.org/10.1140/epjst/e2020-900220-3
THE EUROPEAN PHYSICAL JOURNAL SPECIAL TOPICS
Regular Article
Distortion of surfactant lamellar phases induced by surface roughness? Shirin Nouhi1a , Alexandros Koutsioubas2 , Vassilios Kapaklis1 , and Adrian R. Rennie1,b 1 2
Centre for Neutron Scattering, Uppsala University, 516, 75120 Uppsala, Sweden J¨ ulich Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz Zentrum (MLZ), Forschungszentrum J¨ ulich GmbH, Lichtenbergstr. 1, 85748 Garching, Germany Received 6 October 2019 / Accepted 6 August 2020 Published online 16 November 2020 Abstract. Self-assembly is a characteristic property of soft matter. Understanding the factors which assist or perturb this process is of great importance in many biological and industrial processes. Amphiphiles self-assemble and order into a variety of structures including well-ordered lamellar phases. The present work uses neutron reflectometry and neutron scattering to explore the effects of both interface roughness and temperature on the lamellar-phase structure of a non-ionic surfactant at a solid/liquid interface. The structure of concentrated solutions of tetraethyleneglycol dodecyl ether has been compared against a smooth surface and one with a roughness of the order of the lamellar spacing. This has been done in order to investigate the role perturbations have on the overall lamellar order, when these have length scales of the order of the interactions between neighboring lamellae. The results showed that the surfactant forms a well-ordered and aligned structure at a smooth surface, extending to a depth of several micrometers from the interface. Increasing the temperature of the sample and subsequent cooling promotes alignment and increases the number of oriented layers at the surface. The same sample forms a significantly less aligned structure against a rough surface that does not align to the same extent, even after heating. The perturbation of the structure caused by thermal fluctuations was found to be much less than that imposed by a small surface roughness.
1 Introduction Amphiphiles with hydrophilic head groups and hydrophobic hydrocarbon tail regions occur widely as detergents, in biological membranes and in formulations for personal care and pharmaceutical products, coatings, etc. [1–4]. They self-assemble and order into a variety of structures such as micelles, liquid crystal phases, microemulsions ? Supplementary material in the form of one pdf file available from the Journal web page at https://doi.org/10.1140/epjst/e2020-900220-3 a Present address: SWERIM, Box 7047, SE-164 07 Kista, Sweden b e-mail: [email protected]
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The European Physical Journal Special Topics
and other structures that display both long-range order and interesting dynamics. At solid/liquid interfaces, amphiphiles can organize themselves into well-ordered bilayer and even as multilayer structures. The structure and ordering of molecules at an interface are strongly influenced by both the physical and chemical properties [5,6].
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