Printed parts were designed using Autodesk Inventor 2018. The CAD files were sliced at 50 μM intervals using MII Utility Shortcut V 3.27 and printed using a CADworks3D M50–405 printer (MiiCraft, CADworks3D). The commercial resins included were BV-007A (Clear) (MiiCraft, CADworks 3D), Green Master Mold (MiiCraft, CADworks 3D), Dental LT Clear Resin (V2) (FormLabs), and Asiga PlasClear V2 (iMakr). A house-made photoresin consisting of 0.4 % w/v phenylbis(2,4,6-trimethylbenzoyl)phosphineoxide (Irgacure 819) (Therofisher) dissolved in poly(ethylene glycol) diacrylate (PEG-DA) (MW 250) (Sigma Aldrich) was also included in the suite of resins tested.38 The printer setting for each resin can be found in Table S1. Printed parts were rinsed with either 95% ethanol (Koptec), isopropanol (Fisher chemical), or methanol (Fisher chemical) as recommended for by the manufacturer for the resin. Printed pieces were post-cured in an UV-light box, then stored at room temperature on the bench top in polystyrene petri dishes (Fisher) prior to silanization.
Surface Treatment of 3D Printed Pieces
Where noted, some printed parts were plasma treated using a BD-20AC laboratory corona treater (Electro-Technic Products, Chicago IL, USA). Printed parts were placed 3 mm below the plasma source and treated for 5 – 60 s immediately prior to surface silanization. For gas-phase deposition, 200 μL of neat tridecafluoro-1,1,2,2-tetrahydrooctyl trichlorosilane (Gelest Inc., Morrisville PA, USA) was placed in a vacuum desiccator in a small polypropylene dish, followed immediately by the printed parts, and a vacuum was applied for 2 hours at room temperature. For solvent deposition, the surface of the printed part was submerged in a 10% v/v solution of tridecafluoro-1,1,2,2-tetrahydrooctyl trichlorosilane in solvent (Fluorinert FC-40 (Sigma Aldrich) or 200 proof ethanol (Koptec) for 30 min at room temperature, unless otherwise specified. After silanization, surfaces were rinsed with 95% ethanol and DI water and dried with a nitrogen gun.
Contact Angle Measurement
Surface air/water contact angles were measured using a ramé-hart goniometer (model 200–00, ramé-hart instrument co., Succasunna NJ, USA) and DROPimage Advanced software. Contact angle was measured for 3 separate printed pieces per condition, by pipetting one 5-μL droplet of DI water per print onto the silanized surface. 8×8×8 mm3 cubes were used for the printed piece, and oriented so the smooth flat face of the printed cube was tested.
Surface Chemistry Characterization with Infrared Spectroscopy
The surface chemistry of the printed parts was examined by using an iD7 ATR Nicolet IS5 FT-IR spectrophotometer (Thermo Fischer Scientific). The IR spectrum was measured on the flat smooth face of a 10×10×2 mm3 printed rectangular prism. The instrument was set to a constant gain of 4, and the background was collected prior to each session. Data was collected, visualized, and processed using the OMNIC software (Thermo Fischer Scientific).
Printed pieces were silanized according to the optimized method. To test the resistance to mechanical damage, the parts were clamped with two binder clips against a clean petri dish to apply constant pressure and rubbed together for 30 s at a time. Air/water contact angles of the silanized surfaces were measured before and after the mechanical test. To test stability after storage, silanized printed parts were stored in a petri dish at room temperature under ambient light, and the air/water contact angles were repeatedly measured over time. Finally, contact angles were measured before and after soaking the printed parts for 2 hours in methanol.
Selective Patterning of 3D Printed Surfaces
Rectangular prisms (20×15×3 mm3) were printed using BV-007A resin. Each print contained an embossed cross-shaped open channel with a rectangular cross-section (1 mm deep, 2 mm wide). Scotch tape (3M) was cut and aligned manually to prevent the fluoroalkyl silane solution from coming into contact with portions of the printed surface inside the channel. Taped pieces were immersed in a solution of 10% v/v (tridecafluoro-1,1,2,2-tetrahydrooctyl) trichlorosilane in FC-40 for 30 min in a fume hood at room temperature. After treatment, pieces were rinsed with 95% ethanol and DI water and dried with nitrogen. To test the functionality of the patterned surface, solutions of food coloring in water were pipetted into the arms of the embossed features.
3D printed Droplet Generator
A simple T-junction was designed in AutoCAD, consisting of a 10 mm channel with a 0.5 × 0.5 mm cross-section, with a 3 mm channel length with a 0.5 × 0.5 mm cross-section channel that intersects the longer channel. The enclosed channel was fluorinated by filling the channel with a solution of 10% v/v (tridecafluoro-1,1,2,2-tetrahydrooctyl) trichlorosilane in FC-40 for 30 min, in a fume hood at room temperature. A syringe (1 mL, BD) with a 27 G needle (BD) was filled with FC-40 oil containing 0.5 mg/mL RfOEG (triethyleneglycol mono[1H,1H-perfluorooctyl]ether, a surfactant synthesized in house).29 Another syringe was filled with 1 M Fe(SCN)2+(aq) in water. Connections to the device were made with nonshrinkable PTFE TT-30 tubing (Weico Wire, Edgewood NY, USA). Pressure driven flow was achieved using a Chemyx syringe pump (Fusion 200, Houston TX, USA), using flow rates of 30 μL/min for the oil and 10 μL/min for the aqueous solution. Brightfield images were collected using an Zeiss AxioZoom macroscope (Carl Zeiss Microscopy, Germany) at 1.6 magnification with an Axiocam 506 Mono camera. Images were collected at 1 s intervals for 10 s. All images were analyzed in Zen 2 software.
Statistical tests and curve fitting were performed using Graphpad Prism version 9. Half-lives and half-times of exponential fits were calculated according to half time = ln 2/k, where k is the rate constant from the fit.