Bulk rheology of sticky DNA-functionalized emulsions

We measure by experiment and particle-based simulation the rheology of concentrated, non-Brownian droplet emulsions functionalized with surface-bound single-stranded (ss), "sticky," DNA. In the absence of ssDNA, the emulsion viscosity increases with the dispersed phase volume fraction phi, before passing through a liquid-solid transition at a critical phi c related to random close packing. Introducing ssDNA leads to a liquid-solid transition at phi phi c, the onset being set by the droplet valency N and the ssDNA concentration (or simulated binding strength e). Using insight from simulation, we identify three key behaviors: (i) jammed suspensions (phi phi c and N = 1, 2 always exhibit viscous rheology, regardless of functionalization; and (iii) for phi < phi c and N 3, functionalization leads to a controllable viscous-elastic transition. We present state diagrams showing the range of rheological tuning attainable by these means.