Antireflective Transparent Oleophobic Surface by Non-Interacting Cavities

Abstract

Oleophobic surfaces have been so far realized using complex micro-scale and nano-scale reentrant geometries where primary and secondary structures or overhang geometries are typically required. Here we propose a new design to create them with non-interacting cavities. The suspension of liquid droplets relies on the mechanism of compression of air under the meniscus leading to stable composite oil-air-solid interfaces. To demonstrate the concept, we make oleophobic surfaces, with contact angle for oleic acid of about 130º (and Hexadecane about 110º), using both micro-holes in silicon and nano-holes in glass. Thanks to the subwavelength dimensions and antireflection effect of the nano-holes, the glass substrate also shows a high degree of optical transparency with optical transmission exceeding that of the initial bare substrate. Crockmeter tests without any significant change of morphology, optical and wetting properties after more than 500 passes also confirm the high mechanical durability of the nano-hole surface. The results indicate the possibility of using the proposed oleophobic surfaces for a wide range of applications, including self-cleaning transparent windows, windshields for automobiles and aircrafts.