Robust and Transparent Lossless Directional Omniphobic Ultra-Thin Sticker-Type Film with Re-entrant Micro-Stripe Arrays

Directional droplet-sliding control without wetting the
surface
is immensely required in advanced surface engineering, including biological
and chemical analyses or green technology. However, the development
of robust and transparent thin sticker-type directional omniphobic
films for portable usage in smart microfluidic platforms is rare.
In this study, we report a novel perfluoropolyether (PFPE) directional
omniphobic film (PDOF). The PDOF is a robust and transparent ultra-thin
sticker-type film that can control the anisotropic sliding of various
liquid droplets on the surface. The PFPE is a chemically stable and
turgid material compared to polydimethylsiloxane (PDMS), which is
often used to fabricate liquid-repellent thin films. A well-designed
fabrication criterion through adhesion engineering in the soft-molding
process was developed using the PFPE to obtain a PDOF with a thickness
of 56 μm, with re-entrant micro-stripe structures on the surface.
The fabricated PDOF showed intriguing liquid sliding properties based
on the direction and spacing of the microstructures. This aspect is
defined as an anisotropic factor.