Wrinkled, Dual-Scale Structures of Diamond-Like Carbon (DLC) for Superhydrophobicity

Abstract

We present a simple two-step method to fabricate dual-scale superhydrophobic surfaces by using replica molding of poly(dimethylsiloxane) (PDMS) micropillars, followed by deposition of a thin, hard coating layer of a SiO(x)-incorporated diamond-like carbon (DLC). The resulting surface consists of microscale PDMS pillars covered by nanoscale wrinkles that are induced by residual compressive stress of the DLC coating and a difference in elastic moduli between DLC and PDMS without any external stretching or thermal contraction on the PDMS substrate. We show that the surface exhibits superhydrophobic properties with a static contact angle over 160 degrees for micropillar spacing ratios (interpillar gap divided by diameter) less than 4. A transition of the wetting angle to approximately 130 degrees occurs for larger spacing ratios, changing the wetting from a Cassie-Cassie state (C(m)-C(n)) to a Wenzel-Cassie state (W(m)-C(n)), where m and n denote micro- and nanoscale roughness, respectively. The robust superhydrophobicity of the Cassie-Cassie state is attributed to stability of the Cassie state on the nanoscale wrinkle structures of the hydrophobic DLC coating, which is further explained by a simple mathematical theory on wetting states with decoupling of nano- and microscale roughness in dual scale structures.

Diamond-Like Carbon Coatings with Special Wettability for Automotive Applications

“…Furthermore, hydrophobic fi lms have been successfully deposited on patterned substrates to fabricate superhydrophobic surfaces. Rahmawan et al reported a superhydrophobic surface consisting of a SiO x -DLC fi lm and micropillars of poly(dimethylsiloxane) (PDMS) [ 18 ]. The static contact angle of the fi lm on a Si wafer was measured to be 106.4°.…”

Diffraction-Pattern Based on Spontaneous Wrinkled Thin Films

“…Researches can be roughly divided into two groups concerning to wrinkles application. First is to be the functional patterned surface, such as superhydrophobic coating 5) , high light-harvesting ef ciency device 6) , template for aligning colloidal particles 7) and living cells 8) , tunable optical grating 9) and so on. Second is as a strategy for measuring thickness, elastic moduli, Poisson s ratio, and residual stress 10,11) due to its sensitivity to the mechanical and thermal properties of the system.…”

“…15) In addition, it is a well-established system to get the averaged wavelength of wrinkles since it can minimize measurement error and quickly provide the indispensable information in spite of the diversity and complexity of samples for both off-line and in-situ observation. 5,[16][17][18][19] However, wrinkle surface morphology could also be predicted other than the wavelength by understanding the derivation mechanism from wrinkles to diffraction patterns, which is lacking at present.…”

Water Wetting Observation on a Superhydrophobic Hairy Plant Leaf Using Environmental Scanning Electron Microscopy

“…Lotus leaves exhibit low resistance to water condensation owing to the low aspect ratio (defined as the ratio of the height to the width of the structures, ca. 2 or 3) of the nanopillar structure geometries for nanopillar structures (Cha et al, 2010;Cheng et al, 2005;Rahmawan et al, 2010). The water condensation behavior of particular functional organic surfaces has been measured using environmental scanning electron microscopy (ESEM).…”