Flexible superomniphobic doubly re-entrant (Dual-T) microstructures
inspired by springtails have attracted growing attention due to their
excellent liquid-repellent properties. However, the simple and practical
manufacturing processes of the flexible Dual-T microstructures are
urgently needed. Here, we proposed a one-step molding process coupled
with the lithography technique to fabricate the elastomeric polydimethylsiloxane
(PDMS) Dual-T microstructure surfaces with high uniformity. The angle
between the downward overhang and the horizontal direction could reach
90° (vertical overhang). The flexible superomniphobic Dual-T
microstructure surfaces, without fluorination treatment and physical
treatments, could repel liquids with a surface tension lower than
20 mN m–1 in the Cassie–Baxter state. Owing
to the excellent robustness of the one-step molding downward overhanging,
the max breakthrough pressure of this surface could reach up to 164.3
Pa for ethanol droplets. Furthermore, the flexible superomniphobic
Dual-T surface allowed impinging ethanol droplets to completely rebound
at the Weber number up to 7.1 with an impact velocity of ∼0.32
m s–1. The Dual-T microstructure surface maintained
excellent superomniphobicity even after surface oxygen plasma treatment
and exhibited excellent structural robustness and recoverability to
various large mechanical deformations.
Doubly re-entrant surfaces inspired by springtails exhibit
excellent
repellency to low-surface-tension liquid. However, the flexible doubly
re-entrant surfaces are difficult to fabricate, especially for the
overhang of the structure. Herein, we demonstrate a simple Fresnel
aperture diffraction modulation strategy in microscale lithography
coupled with a molding process to obtain the flexible doubly re-entrant
superomniphobic surfaces with nanoscale overhangs. The negative nanoscale
overhang features were formed in a single-layer photoresist due to
the fine-modulation of the optical intensity fluctuation of the Fresnel
aperture diffraction. The as-prepared flexible non-fluorinated polydimethylsiloxane
(PDMS) doubly re-entrant microstructure based on the Fresnel aperture
diffraction (D-BF) surface (without any additional treatments) could
repel ethanol droplets (21.8 mN m–1) in the Cassie–Baxter
state. The robust nanoscale overhangs obtained by the molding process
enable the maximum breakthrough pressure for the low-surface-tension
ethanol droplets on the D-BF surfaces up to about 230 Pa, allowing
ethanol liquids with Weber numbers up to 8.7 to fully bounce off.
The fabricated non-fluorinated D-BF superomniphobic surface maintains
outstanding liquid repellency after the surface wettability modification
and deformation test.
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