Facile creation of hierarchical PDMS microstructures with extreme underwater superoleophobicity for anti-oil application in microfluidic channels

Abstract

Composition modification and surface microstructures have been widely utilized in interface science to improve the surface performance. In this paper, we observed a significant improvement of oil contact angle (CA) from 66 ± 2° to 120 ± 4° by introducing a radical silanol group on a flat PDMS surface through oxygen plasma pretreatment. By combining surface microstructures and plasma modification, we produced three kinds of superoleophobic surfaces: 20 μm pitch micropillar arrays, 2.5 μm pitch micropillar arrays and gecko foot-like hierarchical microstructures. Among them, the hierarchical surface with high surface roughness showed extreme underwater superoleophobicity, which featured ultrahigh CA (175 ± 3°) and ultrasmall sliding angle (<1°). Quantitative measurements demonstrated that these superoleophobic surfaces exhibited distinct adhesive behaviors, by which they were interpreted as Wenzel's, Cassie's and the Lotus state, respectively. A microfluidic channel with superoleophobic microstructures was further created by novel curve-assisted imprint lithography, and the characterization based on anti-oil contamination applications was carried out and discussed. We believe that the superoleophobic surfaces will power broad applications in oil microdroplet transportation, anti-oil channels and droplet microfluidic systems.

Temperature‐Driven Switching of Water Adhesion on Organogel Surface

“…[ 1 ] In the past few years, our group has achieved great success in developing hydrogel-based materials, forming L 1 / L 2 /solid (LLS) triple-phase system with excellent underwater superoleophobicity, which has broad applications in underwater self-cleaning, [ 2 ] water/oil separation, [ 3 ] control of environmental pollution [ 4 ] and in fi elds of scientifi c research such as non-loss miniature reactors and lab-on-chip devices. [ 5 ] The key factor in realizing underwater oil-repellency is to effectively trap the L 2 (water) on the hierarchical-structured surfaces or on the hydrogel surfaces. Furthermore, due to the existence of water-affi nitive groups, hydrogel can immobilize L 2 (water) on the molecular level by turning free water into bound water via hydrogen bond network, [ 6 ] making the low-oil-adhesion performance stable to harsh environments.…”

Laser interference fabrication of large-area functional periodic structure surface

“…3(c) [19]. The larger period and smaller period structures were superhydrophilic and superoleophilic in the air environment.…”

“…As shown in Fig. 3(a), in situ switching from the pinned to the roll-down state was evident due to the curvature of the surface viewed in macro [18,19]. Structure arrays were fabricated by four-beam interference with a contact angle of 150°AE2°.…”

“…3 (a) Reversible switching of three superhydrophobic states by curvature change and reversible tests for the switching between the pinned and roll-down states; (b) the corresponding state changing in experiment [18]; (c) tilted scanning electron microscopy images of 20 mm period, 2.5 mm period pillar arrays, and hierarchical gecko foot-like microstructures; (d) the contact angle in air and water, and their self-cleaning anti-oil capability on extreme superoleophobic surfaces [19] If n exposures of N-beam interference are found, then the light intensity is expressed as Eq. (4) [12],…”

“…The setup of laser interference is relatively simple, with 2/3/4-beam interferences being the common cases [5,[17][18][19]. Split beams from a coherent laser interfering on the sample are used to form a redistributed fringe-like intensity.…”