Condensed Matter Seminar: Light-induced Reconfiguration and Directed Motion of Chemo-responsive Gels

Wed, 12/03/2014 - 16:00 - 18:00
Anna C. Balazs, University of Pittsburgh

A remarkable feature of certain biological organisms is their ability to alter their shape and functionality in response to environmental cues. Polymer gels undergoing the Belousov-Zhabotinsky (BZ) reaction are unique self-oscillating materials that can be used to design a variety of soft materials with biomimetic functionality. We focus on chemically-mediated communication between multiple pieces of BZ gels. We show that the system exhibits autochemotaxis, which results in a spontaneous self-aggregation of the pieces. We also find that the aggregated structure can undergo spontaneous, autonomous rotation. Moreover, the gels’ coordinated motion can be controlled by light, allowing us to achieve selective self-aggregation and control over the shape and motion of the aggregates. We then focus on novel polymer gels that combine two distinct functionalities. First, these gels contain spirobenzopyran (SP) chromophores grafted onto the polymer matrix; the SP moieties are hydrophilic in the dark in an acidic aqueous solution, but become hydrophobic under illumination with blue light. Hence, incorporation of these chromophores into the gel allows us to remotely control the gel's swelling or shrinking. Second, these gels also contain a Ru catalyst that is grafted onto the polymer chains. When placed into a solution containing all the reagents needed for the Belousov-Zhabotinsky (BZ) reaction, these SP-BZ gels undergo self-oscillations. We show that these systems undergo large scale shape changes, with an initially flat sheet morphing into a variety of complicated 3D forms. Moreover, these SP-BZ gels undergo self-propelled motion, with the mode of motion being controlled by external light. Our results point to a novel class of active self-oscillating materials and to a robust method for controllably re-configuring their 3D shapes and their self-propelled motion.