# Magnetic cylindrical colloids at liquid interfaces exhibit non-volatile switching of their orientation in an external field

## Authors

Bethany J. Newton

##### Abstract

We study the orientation of magnetic cylindrical particles adsorbed at a liquid interface in an external field using analytical theory and high resolution finite element simulations. Cylindrical particles are interesting since they possess multiple locally stable orientations at the liquid interface so that the orientational transitions induced by an external field will not disappear when the external field is removed, i.e., the switching effect is \emph{non-volatile}. We show that, in the absence of an external field, as we reduce the aspect ratio $\alpha$ of the cylinders below a critical value ($\alpha_c \approx 2$) the particles undergo spontaneous symmetry breaking from a stable side-on state to one of two equivalent stable tilted states, similar to the spontaneous magnetisation of a ferromagnet going through the Curie point. By tuning both the aspect ratio and contact angle of the cylinders, we show that it is possible to engineer particles that have one, two, three or four locally stable orientations. We also find that the magnetic responses of cylinders with one or two stable states are similar to that of paramagnets and ferromagnets respectively, while the magnetic response of systems with three or four stable states are even more complex and have no analogs in simple magnetic systems. Magnetic cylinders at liquid interfaces therefore provide a facile method for creating switchable functional monolayers where we can use an external field to induce multiple non-volatile changes in particle orientation and self-assembled structure.

 Publication Date Jun 28, 2016 Journal Soft matter Print ISSN 1744-683X Electronic ISSN 1744-6848 Publisher Royal Society of Chemistry Peer Reviewed Peer Reviewed Volume 12 Issue 24 Pages 5285-5296 Institution Citation Newton, B. J., & Buzza, D. M. A. (2016). Magnetic cylindrical colloids at liquid interfaces exhibit non-volatile switching of their orientation in an external field. Soft matter, 12(24), 5285-5296. https://doi.org/10.1039/c6sm00136j DOI https://doi.org/10.1039/c6sm00136j Keywords Magnetic cylindrical colloids; Liquid interfaces; Non-volatile switching Publisher URL http://pubs.rsc.org/en/Content/ArticleLanding/2016/SM/C6SM00136J#!divAbstract Additional Information Authors' accepted manuscript of article published in: Soft matter, 2016, v.12, issue 24.

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