Collective Dynamics of Magnetically-Driven Colloids

Abstract:  

Colloidal suspensions driven out of equilibrium exhibit rich and unexpected behaviors, from dynamic clustering to self-organized phase coexistence. These nonequilibrium systems challenge conventional thermodynamic intuition, yet their dynamics often resemble equilibrium phase transitions such as crystallization, condensation, and phase separation. By leveraging time-varying magnetic fields, we explore new avenues for controlling soft matter systems and uncover emergent material properties. I will first introduce the collective behavior of superparamagnetic colloids under rotating magnetic fields. These driven particles self-organize into a steady-state vapor-liquid coexistence, reminiscent of equilibrium phase transitions. Using Kelvin’s equation, we extract an “effective vapor pressure” for this nonequilibrium system, offering a new statistical mechanics framework to describe active matter. In the second example, I will introduce a magnetically tunable colloidal model for semiflexible filaments, composed of DNA-linked paramagnetic beads. These engineered chains exhibit persistence lengths spanning five orders of magnitude, allowing us to probe the intricate balance between external forces, viscous dissipation, and filament elasticity. In dynamic magnetic fields, these filaments undergo buckling, coiling, and other emergent motions that provide design principles for microbots and rheological probes.

Bio:

Dr. Lisa Biswal is the Department Chair and William M. McCardell Professor in the Department of Chemical and Biomolecular Engineering at Rice University in Houston, Texas. She has a B.S in chemical engineering from Caltech and a Ph.D. in chemical engineering from Stanford University. She leads the Soft Matter Engineering Laboratory, where she focuses on establishing connections between the rheological behaviour of particulate and multiphase systems and the underlying physics governing colloidal assemblies, surfactant stabilization related to foams and emulsions, and the development of polymer composites for batteries. Her research aims to uncover new insights and ideas that can be used to engineer innovative solutions for a diverse range of technological challenges in the fields of materials and energy. She is the recipient of the 2025 Provost’s Award for Outstanding Doctoral Advisor. She is also Fellow of the American Physical Society (APS) and the American Institute of Chemical Engineers (AICHE)