MATERIALS SCIENCE COLLOQUIUM

Refreshments will be served at 10:45 a.m.

ABSTRACT: Self-assembly, a natural tendency of simple building blocks to organize into complex architectures is a unique opportunity for contemporary materials science. In order to support structural complexity and functional diversity, self-assembled materials must actively consume energy and “live” out of equilibrium. We study a variety of simple active colloidal systems: from a suspension of swimming bacteria to a ferromagnetic colloidal suspension confined at the interface between two immiscible liquids and energized by an alternating magnetic field. We have designed a hybrid bio-mechanical system in which common aerobic bacteria Bacillus subtilis, swimming in a free-standing fluid film, power sub-millimeter gears decorated with asymmetric teeth. For a ferromagnetic colloidal suspension, a variety of dynamic self-assembled structures is observed: from self-propelled magnetic swimmers - magnetic snakes to localized asters and arrays of asters. The asters, remotely controlled by an external magnetic field, perform simple robotic functions including capture, transport, and positioning of target particles. Observed phenomena are described by a first-principles mathematical model for the dynamic self-assembly of magnetic colloids at a water-air interface. Our work provides new insights into the design and fabrication of “smart” synthetic materials with self-repairing, multitasking, and reconfiguring capabilities.