Design and synthesis of an azobenzene–betaine surfactant for photo-rheological fluids
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Date
2021-07-15
Journal Title
Journal ISSN
Volume Title
Publisher
Elsevier
Abstract
Hypothesis
Morphology of surfactant self-assemblies are governed by the intermolecular interactions and packing constraints of the constituent molecules. Therefore, rational design of surfactant structure should allow targeting of the specific self-assembly modes, such as wormlike micelles (WLMs). By inclusion of an appropriate photo-responsive functionality to a surfactant molecule, light-based control of formulation properties without the need for additives can be achieved.
Experiments
A novel azobenzene-containing surfactant was synthesised with the intention of producing photo-responsive wormlike micelles. Aggregation of the molecule in its cis and trans isomers, and its concomitant flow properties, were characterised using UV–vis spectroscopy, small-angle neutron scattering, and rheological measurements. Finally, the fluids capacity for mediating particle diffusion was assessed using dynamic light scattering.
Findings
The trans isomer of the novel azo-surfactant was found to form a viscoelastic WLM network, which transitioned to inviscid ellipsoidal aggregates upon photo-switching to the cis isomer. This was accompanied by changes in zero-shear viscosity up to 16,000x.UV–vis spectroscopic and rheo-SANS analysis revealed interactions of the trans azobenzene chromophore within the micelles, influencing aggregate structure and contributing to micellar rigidity. Particles dispersed in a 1 wt% surfactant solution showed a fivefold increase in apparent diffusion coefficient after UV-irradiation of the mixture. Crown Copyright © 2021 Published by Elsevier Inc.
Description
Keywords
Neutron diffraction, Synthesis, Rheology, Surfactants, Betaine, Visible radiation
Citation
Butler, C. S. G., King, J. P., Giles, L. W., Marlow, J. B., Vidallon, M. L. P., Sokolova, A., de Campo, L., Tuck, K. L. & Tabor, R. F. (2021). Design and synthesis of an azobenzene–betaine surfactant for photo-rheological fluids. Journal of Colloid and Interface Science, 594, 669-680. doi:10.1016/j.jcis.2021.02.061