by De = λv L$_{Char}$ ≈ λ$_{Zimm}$µ$_{EOF}$E L$_{Char}$ . (1) We estimate the relaxation time λ of our liquid using the Zimm estimate λ$_{Zimm}$ ≈ 0.03 s and L$_{Char}$ ≈ 12 µ m for our channels; see Ref. [22]. For our setup and polymer De > 1/2 for driving voltages ≳ 20 V, and here we operate well above the threshold at 200 V to ensure highly unstable flows. As we find µ$_{EOF}$ is not modified by the presence of polymer in the dilute concentration regime all flows are comparable. The strategy to promote instabilities discussed here is simple. The addition of polymer is facilitated if pre-solvated polymer mixtures are added to working fluids. The use of high viscosity solvents or concentrated polymer is not required: low viscosity, lightly polymer doped liquids undergo instability under typical electro-osmotic flow conditions. The mixing efficiency is found by measuring the homogeneity of a fluid domain [27], and here is calculated using the first moment mixing index where c is the dye concentration and c the average concentration; for unmixed streams M1 = 1 and mixing is perfect for M1 = 0 (homogenous). In “normal” microfluidics smooth laminar flows are observed, as seen in Fig. 2 for our polymer-free solutions. As the fluid flows downstream diffusion across the channel will eventually result in homogenously mixed fluid (not show). We observe that mixing values for polymer-free flows scale approximately exponentially as a function of distance downstream; while perfect exponential scaling is not expected calculating M1 using the theoretical erf- profile [28] for laminar mixing in uniform channels results in an approximate exponential drop off [45]. Addition of polymer results in large instabilities, as can be seen in Fig. 3 and Fig. 4. The fluctuations move material transverse to the flow direction, spanning almost the entire channel. There is no dominant frequency in the flow, indicating chaotic flow [14], and the overall pattern displayed are striations with “comb-like” teeth randomly spaced. Increasing the concentration from 32 to 64 ppm results in larger fluctuations and tooth spacing. As the solutions move downstream through additional elongation regions additional striations 6 M1 = 〈| c − c |〉 c (2)