Ptfe membrane

Designs of
the microfluidic recycler device were finished in Autodesk Inventor
Professional 2022 (details and measurements are available in the Supporting Information). The device was fabricated
by a stereolithographic 3D printer (Asiga, MAX X UV385) with a transparent
methacrylate-based resin, GR-10 (Pro3dure Medical). The as-printed
device was thoroughly washed in three consecutive 2-propanol (IPA)
baths right after being removed from the printer. IPA was also injected
using a 20 mL syringe to flush the internal channel. The device was
then immersed in IPA in a glass beaker and placed in an ultrasonic
bath (Elma, E15H) at 30 °C for 20 min and air-dried completely
prior to the next step. A piece of polytetrafluoroethylene (PTFE)
membrane with pore size 0.1 μm (Sterlitech) was cut to a proper
shape and placed on the separation position of the recycler. A quick-cure
epoxy (Bob Smith Industries) was applied to combine the two halves
of the recycler. The recycler sat for 2 h to allow full curing of
the epoxy. 200 μL of either BMIM-NTf₂ or BMPYRR-NTf₂ was injected into the recycler to prewet the membrane, and
the excessive IL was withdrawn after the 2 h incubation.

To fabricate the liquid-infused film used for electrowetting, the transparent glass substrate coated with Indium Tin Oxide (ITO) was first cleaned by plasma for ~30 min. After cleaning, the PTFE membrane (thickness ~ 20 μm, Sterlitech Corporation) was gently placed on the top of ITO glass slide. To make the PTFE membrane smooth and be of good contact with the ITO substrate, we wet the membrane using ethanol with the help of capillary wicking effect. Then after the evaporation of ethanol, we added the liquid lubricant with a pre-determined volume into the membrane. In our experiment, the low surface tension 3 M Fluorinert FC-70 (γ ≈ 18 mN/m, η ≈ 12 cSt) and Dupont Krytox GPL 103 (γ ≈ 16 ~ 20 mN/m, η ≈ 80 cSt) were chosen as liquid lubricants to spread on PTFE membrane and form a stable film via capillary wicking. The thickness of the liquid-infused film H is determined by the fluid volume V according to the equation H = (V + m/ρ)/S, where ρ is the PTFE membrane density, m and S are the weight (measured by analytical balance, AY220, Shimadzu) and the surface area of the membrane, respectively. In our experiment, the thickness of the as-prepared liquid-infused film was tailored to ~20 μm and ~50 μm, respectively.