IRG 2: Activated Architectured Materials

Senior Participants (*=coordinators): J. de Pablo, M. Gardel, W. Irvine, K.Y. Lee, *J. Park, D. Talapin, S. Vaikuntathan, *V. Vitelli, T. Witten

The vision for IRG2 is to design and build shape-morphing hybrid materials with transport properties that are programmable and spatiotemporally self-regulating.  Gaining the ability to create active materials with distributed microscopic elements that convert energy into local mechanical work would fundamentally alter existing approaches to materials design. Such materials are ubiquitous in biology, where they impart autonomy to living systems. Inspired by nature, we will design and build hybrid inorganic-biological materials that sense and interact with the enviroment to produce an “artificial” skin, or active ink-jet drops to enable reconfigurable printing. The platform on which such technologies will be developed will consist of “activated” materials. By this term we designate materials that operate inherently out of equilibrium because they are comprised of (i) chemically active components, e.g., molecular motors, (ii) building blocks driven by suitably tailored external fields, or (iii) both, acting in tandem. Research on active matter has long sought to create such materials, but attempts to date, including those by our MRSEC, have been restricted to living systems that contain mechanoenzymes or limited classes of model systems (e.g. colloidal swimmers and chiral fluids).

This IRG seeks to capitalize on new opportunities that arise when approaches from active matter are combined with recent advances in the synthesis of inorganic materials that exploit their unique mechanical, optical, thermal and electrical properties. The resulting hybrid structures, which we refer to as activated architectured materials, will harness the feedback between activation, local architecture and transport. That feedback can proceed along two distinct routes, shown as blue and orange arrows ibelow In Route 1 (blue arrows), activation modifies transport properties, e.g. the viscosity of an active fluid, leading to additional active stresses that can then change material architecture, e.g., the shape of a droplet. In Route 2 (orange arrows), activation directly impacts the structure of a material, e.g., the conformation of an activated sheet, which in turn leads to modification of its thermal transport properties.

This IRG is organized to take advantage of exciting opportunities in this field, and builds on strengths developed by the UChicago MRSEC. In FA1, we explore Route 1 using activated fluids composed of self-spinning colloids and nanoparticles as model systems. Here, modulations in the external drive provide a means for spatio- temporal control of active stresses, paving the way for self-printing ink-jet drops. We call these fluids metafluids, in analogy with metamaterials, because their properties are engineered by a suitably controlled external drive. FA2 explores Route 2 using activated sheets composed of hybrid passive-inorganic and active-biological components. Thin sheets offer a particularly promising platform arising from the soft bending modes that can be activated by bio-molecular motors. Here, shape-shifting materials powered by active stresses will be employed to control optical and thermal conductivity. FA3 brings together elements of FA1 and FA2, and considers composite structures with multiple independent sources of activation, such as “artificial skin” constructed by combining epithelial cells - which are themselves chemically active, with soft polymer electronics that provide an additional source of activation imparted by electric stimuli. Here, we will attempt to achieve in engineered materials the level of integrated bio-mechanical functionalities that are typically associated with living systems.

Activation as an order parameter for materials design. Material components (gray circles) are activated with spatial and/or time control (α(x,t)) to drive local motion and force (red arrow). This local activation is used to control material response through two routes, as described in the text.