Light-induced Patterning and Grafting for Slippery Surfaces based on Silane-coated Nanoporous Structures

Our research introduces a DLP-based technique to fabricate spatial pattern SLIPS, addressing limitation in achieving selective availability control. Key experimental challenges include fabricating sleeves on complex geometric, existing method are time-consuming, multi-step, and lack high-resolution or selective variability. To begin, mix the photocurable polyurethane acrylate resin with PEG 200 at a weight ratio of 50%Using a magnetic stirrer, stir the mixture at 500 revolutions per minute for five minutes.

Dispense the mixed solution as sessile droplets onto a polyethylene terephthalate film. Cover the droplets with a fluorinated ethylene propylene film. And apply uniform pressure using a roll-to-plate system to ensure even spreading.

Expose the polyurethane acrylate resin to ultraviolet light at 365 nanometers using a light-emitting diode ultraviolet curing system. After polymerization, remove the fluorinated ethylene propylene films from the surface. Now immerse the cured specimen in deionized water for one hour to extract unreactive PEG 200.

Dry the sample in an oven at 70 degrees Celsius for one hour to remove residual water and complete fabrication of the nanoporous surface. Perform ultraviolet ozone treatment at 185 and 254 nanometers to introduce hydroxyl groups as pre-treatment for self-assembled monolayer formation. Next, place a hot plate inside a nitrogen filled glove box.

Position a clean beaker on the hot plate and dispense one milliliter of OTS solution as a sessile droplet at the bottom. Secure the PET film specimens onto glass slides. Place the slides face down over the beaker to initiate vapor phase deposition of OTS.

Heat the setup to 120 degrees Celsius for 40 minutes. Now remove the specimens from the glove box. Clean the beaker using a lint-free wipe to eliminate any residual OTS.

For light induced grafting, perform ultraviolet ozone treatment at 185 and 254 nanometers on the OTS-coated surface. Now apply 20 microliters per square centimeter of 10 centistoke silicone oil to the surface by sessile droplet deposition. Irradiate the specimen for 15 minutes with a high-intensity ultraviolet lamp, placed 15 centimeters above the surface.

Then tilt the specimen at a 30 degree angle and hold the position for five minutes to allow excess silicone oil to drain off the surface. To fabricate the pattern slippery structure, first, design the desired shapes using CAD software and export as stereo lithography files. Load the files into slicing software and generate two dimensional projection images for digital light processing.

Transfer the files to the three dimensional printer. Place the polymer-coated film onto the digital light processing printer window. Expose the film to 365 nanometers ultraviolet light at 180 millijoules per square centimeter with the digital projection pattern to selectively cure the resin.

Submerge the exposed sample in deionized water for one hour to extract PEG 200. Then dry the sample at 70 degrees Celsius for one hour to remove residual water and complete the nanoporous structure. Conduct OTS treatment and light-induced grafting to complete the fabrication of the pattern slippery surfaces.

The nano porous surfaces fabricated via polymerization-induced phase separation exhibited a dominant pore size distribution of 60 to 100 nanometers. The static water contact angle measured on the porous surface was 84.4 degrees. After silanization, the surface became hydrophobic, but a second ultraviolet ozone treatment temporarily reduced the contact angle.

This reduction was reversed by PDMS brush layer formation, which restored hydrophobicity. The slippery behavior of four representative liquids:deionized water, octane, honey, and artificial human saliva was validated by contact angle, sliding angle, sliding speed, and contact angle hysteresis measurements. Printed line width measurements from the PEG, PUA resin showed high fidelity at the minimum feature size of 50 micrometers, with increasing deviations at larger widths.

Patterned nanoporous surfaces were fabricated with graphical and letter designs using digital light processing, including maze, gear, and JoVE logos. Following all surface treatments and silicone oil infusion, the patterns became optically transparent due to reduced refractive index contrast. Transmittance measurements showed that treated porous surfaces reached over 90%transparency.

When water containing ink was applied, droplets selectively migrated to untreated hydrophilic regions, avoiding the slippery domains, forming defined liquid shapes. We found that when we make nanoporous surface with UVU grafting, they become very slippery. The contact angle hysteresis is really small, so we can create selective droplet patterns on the surface.

Our method use DLP 3D printing so we can pattern the surface in a single, faster step with a high-resolution. It also works on a flexible substrate. Compared to typical multi-step process, it is very simple and very quick.

Because we can control where the surface is wettable or slippery, we can guide how droplets move and stay on a surface. This can help future work on things like directional droplet transport, microfluidic device, self-cleaning coatings, and even water harvesting surface.