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Issue 11, 2020
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A single-component photorheological fluid with light-responsive viscosity

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Viscoelastic fluids whose rheological properties are tunable with light have the potential to deliver significant impact in fields relying on a change in flow behavior, such as in-use tuning of combined efficient heat-transfer and drag-reduction agents, microfluidic flow and controlled encapsulation and release. However, simple, single-component systems must be developed to allow integration with these applications. Here, we report a single-component viscoelastic fluid, capable of a dramatic light-sensitive rheological response, from a neutral azobenzene photosurfactant, 4-hexyl-4′butyloxymonotetraethylene glycol (C6AzoOC4E4) in water. From cryo-transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS) and rheology measurements, we observe that the photosurfactant forms an entangled network of wormlike micelles in water, with a high viscosity (28 Pa s) and viscoelastic behaviour. UV irradiation of the surfactant solution creates a less dense micellar network, with some vesicle formation. As a result, the solution viscosity is reduced by four orders of magnitude (to 1.2 × 10−3 Pa s). This process is reversible and the high and low viscosity states can be cycled several times, through alternating UV and blue light irradiation.

Graphical abstract: A single-component photorheological fluid with light-responsive viscosity

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Article information

06 Dec 2019
05 Mar 2020
First published
12 Mar 2020

Nanoscale, 2020,12, 6300-6306
Article type

A single-component photorheological fluid with light-responsive viscosity

E. A. Kelly, N. Willis-Fox, J. E. Houston, C. Blayo, G. Divitini, N. Cowieson, R. Daly and R. C. Evans, Nanoscale, 2020, 12, 6300
DOI: 10.1039/C9NR10350C

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