Mechanically Switchable Wetting Petal Effect in Self-Patterned Nanocolumnar Films on Poly(dimethylsiloxane)

Abstract

Switchable mechanically induced changes in the wetting behavior of surfaces are of paramount importance for advanced microfluidic, self-cleaning and biomedical applications. In this work we show that the well-known polydimethylsiloxane (PDMS) elastomer develops self-patterning when it is coated with nanostructured TiO2 films prepared by physical vapor deposition at glancing angles and subsequently subjected to a mechanical deformation. Thus, unlike the disordered wrinkled surfaces typically created by deformation of the bare elastomer, well-ordered and aligned micro-scaled grooves form on TiO2/PDMS after the first post-deposition bending or stretching event. These regularly patterned surfaces can be reversibly modified by mechanical deformation, thereby inducing a switchable and reversible wetting petal effect and the sliding of liquid droplets. When performed in a dynamic way, this mechanical actuation produces a unique capacity of liquid droplets (water and diiodomethane) transport and tweezing, this latter through their selective capture and release depending on their volume and chemical characteristics. Scanning electron and atomic force microscopy studies of the strained samples showed that a dual-scale roughness, a parallel alignment of patterned grooves and their reversible widening upon deformation, are critical factors controlling this singular sliding behavior and the possibility to tailor their response by the appropriate manufacturing of surface structures.

Fundamentals and utilization of solid/ liquid phase boundary interactions on functional surfaces

“…Another promising way of wettability regulation is the utilization of mechanical stimuli to alter surface texture [183]. In most of the literature examples of this feature, elastomeric matrix materials, such as PDMS [184,185] are applied to promote reversible transitions. To produce uniform response, these surfaces possess highly ordered structure, which can be elaborated via destructive methods, such as photo-or plasma etching [186].…”

Multifunctional Biomimetic Composite Coating with Antireflection, Self-Cleaning and Mechanical Stability

“…However, large-area preparation of biomimetic coatings with excellent antireflective and superhydrophobic self-cleaning properties remains a challenge. Currently, the chemical/physical vapor deposition method [ 16 , 17 , 18 ], electrochemical machining method [ 19 , 20 , 21 ], and the femtosecond laser method [ 22 , 23 ] are mainly used to fabricate functional coatings on metal substrate. In particular, large-scale application of these techniques is difficult due to the complex preparation process, high cost, and single surface function.…”