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 𝜙, before passing through a liquid-solid transition at a critical 𝜙𝑐 related to random close packing. Introducing ssDNA leads to a liquid-solid transition at 𝜙<𝜙𝑐, the onset being set by the droplet valency 𝑁 and the ssDNA concentration (or simulated binding strength 𝜀). Using insight from simulation, we identify three key behaviors: (i) jammed suspensions (𝜙>𝜙𝑐≈0.64) show weak effects of functionalization, with elastic rheology instead governed by droplet stiffness; (ii) suspensions with 𝜙<𝜙𝑐 and 𝑁=1, 2 always exhibit viscous rheology, regardless of functionalization; and (iii) for 𝜙<𝜙𝑐 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.