Paper Number
SC59 

Session
Suspensions and Colloids

Title
Rotational dynamics in a back-and-forth rotating magnetic field

Presentation Date and Time
October 13, 2022 (Thursday) 10:55

Track / Room
Track 1 / Sheraton 4

Authors (Click on name to view author profile)

1. Lobmeyer, Dana M. (Rice University, Chemical and Biomolecular Engineering)
2. Spatafora-Salazar, Aldo S. (Rice University, Department of Chemical and Biomolecular Engineering)
3. Cunha, Lucas Hildebrand (Rice University, Chemical and Biomolecular Engineering)
4. Joshi, Kedar (Indian Institute of Technology Goa, School of chemical and material sciences)
5. Biswal, Sibani Lisa (Rice University, Chemical and Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
Dana M. Lobmeyer¹, Aldo S. Spatafora-Salazar¹, Lucas Hildebrand Cunha¹, Kedar Joshi² and Sibani Lisa Biswal^1
1Chemical and Biomolecular Engineering, Rice University, Houston, TX 77005; ²School of chemical and material sciences, Indian Institute of Technology Goa, Ponda, Goa 403401, India

Speaker / Presenter 
Lobmeyer, Dana M.

Keywords
colloids; directed systems

Text of Abstract
Rotating magnetic fields (RMFs) have become a useful tool in directing the two-dimensional assembly of magnetic colloids. While RMFs assemble particles by producing an effectively isotropic attractive interaction, they have also been shown to produce a collective rotational motion in large particle systems. To suppress this rotational motion while maintaining isotropic interactions, a back-and-forth field has been used, where the rotating field changes direction every other period. However, effectively isotropic interactions in the back-and-forth field have not been verified. In this work, we probe a two-particle system of superparamagnetic particles to elucidate particle-particle interactions in the back-and-forth field. Through experimental rotational dynamics, we showcase anisotropy in the particle-particle interactions, thereby refuting the claim that isotropic interactions are maintained under this type of field. We present the preferred alignment of these particle pairs in the direction tangential to where the field turns around, thereby creating an angular trap. Lastly, we elucidate the presence of lateral interactions that cause the field to appear to have isotropic interactions in larger particle systems. Understanding how colloidal assembly is impacted by relatively small changes in the directing magnetic field paves the way for fine tune control at the colloidal scale.