Paper Number
AD8
Session
Rheology of Active Matter and Directed Systems
Title
Assembly of paramagnetic colloidal clusters in a back-and-forth rotating magnetic field
Presentation Date and Time
October 12, 2022 (Wednesday) 4:25
Track / Room
Track 4 / Michigan AB
Authors
- Spatafora-Salazar, Aldo S. (Rice University, Department of Chemical and Biomolecular Engineering)
- Lobmeyer, Dana M. (Rice University, Chemical and Biomolecular Engineering)
- Biswal, Sibani Lisa (Rice University, Chemical and Biomolecular Engineering)
Author and Affiliation Lines
Aldo S. Spatafora-Salazar, Dana M. Lobmeyer and Sibani Lisa Biswal
Chemical and Biomolecular Engineering, Rice University, Houston, TX 77005
Speaker / Presenter
Spatafora-Salazar, Aldo S.
Keywords
colloids; directed systems; microscopy
Text of Abstract
Applying high-frequency rotating magnetic fields (RMFs) to a suspension of magnetic colloids induces an effectively isotropic interaction potential among the particles that drives their organization into two-dimensional (2D) clusters with crystalline order. The clusters of superparamagnetic particles under an RMF acquire an effective circular shape and rotate in the direction of the field. Suppression of cluster rotation can be achieved by applying a “back-and-forth” field, consisting of a rotating field that inverts the direction of its rotation at the end of every period. However, it is unclear if other structural changes occur because of this field. In this work we investigate the impact that such a field has on the assembly of superparamagnetic particles into clusters. In contrast to the conventional RMF, we find that the clusters become anisotropic in shape and display a preferred orientation as the amplitude of the magnetic field increases. The director of the clusters coincides with the tangent direction to the point of inversion of the “back-and-forth” RMF. At long times, we observe that the strength of the cluster alignment can decrease as clusters coalesce laterally with respect to the director and do not realign. The lack of realignment with the director, combined with slower growth kinetics than those found in clusters in a conventional RMF, suggests that the colloidal system is in an arrested state. Our work implies that small changes in external driving have a significant effect on the organization and control of polarizable particles, allowing for novel ways to direct colloidal assembly for the design of structured materials.