ChE Seminar: Sibani Lisa Biswal, Rice University, “Driving Colloids Out of Equilibrium: Chain Dynamics and Emergent Phases”

Content

Host:  Peter Beltramo
 

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 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. 

In a second example, we examine 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.