Using external fields to control the behaviour of anisotropic particles at liquid interfaces

Newton, Bethany Jade

Abstract

In this thesis we use analytical theory and high resolution finite element simulations (using the program ‘Surface Evolver’) to consider the influence of an external magnetic field on the orientation and self-assembly of rod-like magnetic particles.

Firstly, we calculate the equilibrium tilt angle with respect to the undeformed interface and the meniscus shape around an ellipsoidal particle when a magnetic field is applied perpendicular to the interface. As we increase field strength, the particle undergoes a discontinuous transition to the ‘perpendicular’ orientation. We show that it is necessary to include meniscus deformations in our calculations in order to accurately model this transition. We also show for the first time that the tilt angle vs. magnetic field curve exhibits hysteresis behaviour.

Secondly, we study the orientation of magnetic cylindrical particles. For cylindrical particles at a liquid interface, orientational transitions induced by an external field remain when the external field is removed i.e. the switching effect is non-volatile. By tuning both the aspect ratio and contact angle, we show that it is possible to engineer cylindrical particles that have multiple locally stable orientations and hence obtain extremely rich magnetic responses to an external field. We show that such systems provide a facile platform for creating switchable functional materials.

Finally, we investigate the interactions between, and self-assembly of, multiple ellipsoidal particles. For two ellipsoidal particles, the only stable configuration was found to be the side-to-side configuration. However, for three ellipsoidal particles, the tip-to-tip configuration was also found to be locally stable. There is good qualitative agreement between our finite element simulations and a linearised analytical theory and we attribute quantitative discrepancies between the two to non-linear and many-body effects.

Citation

Newton, B. J. Using external fields to control the behaviour of anisotropic particles at liquid interfaces. (Thesis). University of Hull. https://hull-repository.worktribe.com/output/4219525

• Thesis Type: Thesis
• Deposit Date: Aug 24, 2017
• Publicly Available Date: Feb 23, 2023
• Keywords: Physics
• Public URL: https://hull-repository.worktribe.com/output/4219525
• Additional Information: Department of Physics, The University of Hull
• Award Date: Aug 1, 2016