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Wednesday, November 1, 2017 at 4:00pm to 5:00pm
Clark Hall, 700
Nate Cira, The Rowland Institute, Harvard University
Host: Iwijn de Vlaminck
Boundary conditions in soft matter: dancing droplets and elastomeric focusing
Boundary conditions can have profound effects on otherwise well understood systems. Here I present two different examples, one with liquids and one with elastomers. In the first example, instead of spreading completely flat on wetting surfaces, certain two-chemical combinations form stable droplets. Furthermore, these droplets have unique properties such as absence of contact line pinning, which allows them to respond to minute forces, giving rise to life-like behaviors such as chemotaxis and chasing. I show how evaporation and surface tension gradients at the droplet surface lead to this unique state and that the effects can be leveraged to create droplet machines. In the second example, confining an elastomeric material by rigid materials at the boundaries enables amplified displacements upon expansion of the elastomer. I show how this "elastomeric focusing" effect enables micromechanical actuators which can be used as fluidic valves. These valves can be controlled optically, or directly with a small amount of electrical power, enabling portable complex liquid handling systems.