New strategies for memory formation and disruption in non-equilibrium materials*

Embedding physical memory into materials is of crucial importance to a range of technologically important materials including gels, polymers, and suspensions as well as shape memory alloys and ceramics. Despite their importance, there are very few strategies for imparting memory into such materials, which limits their use in applications. Here, I discuss new strategies for creating and destroying memories in three of these systems: gels, suspensions, and shape memory actuators. First, I will show that oscillatory shear training can embed memories of specific shear protocols in colloidal gels and that such systems can support memories both along and orthogonal to the training flow direction. Second, I will discuss memories in the context of shear thickening suspensions where disruption of the force chains responsible for thickening, i.e. erasing the flow induced memory, can be used to dethicken the suspension. Third, I will discuss a new class of reconfigurable micron-scale shape memory actuators. They function by the electrochemical oxidation/reduction of a nm thin platinum film surface, creating a strain in the oxidized layer that causes bending. They, operate at moderate voltages (~1 V), bend to the smallest radius of curvature of any electrically controlled microactuator (~ 500 nm), and are fast (< 100 ms operation). Finally, I will discuss various applications of tuning memory in these gels, suspensions, and actuators for technologies ranging from food preparation, to geological flows, and even microscoic robots.