FIG. 6: Mixing as a function of concentration in the 2 nd expansion unit, as measured by the first moment mixing index M1 (M1 → 0 for perfect mixing and M1 → 1 for no mixing). Using space- time diagrams mixing is measured for c = 16, 32, 64, 128, and 256 ppm (the overlap concentration is c$_{∗}$ ≈ 300); error in M1 is estimated as ≲ 5%. The mixing index slowly raises with concentration in the dilute regime; this indicates that while instabilities are promoted by the presence of polymers absolute mixing is reduced (diffusion is hindered by the presence of polymers). The lack of enhanced diffusion demonstrates that small scale instabilities are not excited to any significant extent. FIG. 7: Mixing as a function of constriction unit, as measured by the first moment mixing index M1. Using space-time diagrams mixing was measured downstream of the initial junction at N=2, 4, 8. The mixing index scales exponentially, and the mixing lengths mildly reduce with concentration (4.5 for 0 ppm, 4.2 for 32 ppm, and 3.2 for 64 ppm). The vertical shift for polymer doped fluids relative to undoped fluid is due to reduced diffusion limiting the mixing, as increased polymer concentration reduces the diffusion constant by increasing viscosity. elastic turbulence which has been shown to be a realization of Batchelor turbulence [38, 39]. In Batchelor turbulence it has been established that the velocity spectrum decays rapidly (the wavenumber k scales as k − $^{x}$, where x has experimentally been found to be in the 11