Repellent surfaces. Turning a surface superrepellent even to completely wetting liquids (original) (raw)

Characterization of super liquid-repellent surfaces

Current Opinion in Colloid & Interface Science, 2014

Characterization of the wetting properties is a prerequisite for a fundamental understanding and the targeted development of superhydrophobic and superamphiphobic layers. To fabricate super liquid-repellent layers, two requirements need to be met: The surfaces have to be of low energy and their nano-and microstructure needs to be designed in a way that leads to the entrapment of air. The challenge is to design and produce suitable nano-and microstructures to control wetting. Here we describe important methods to quantify wetting properties of super liquid-repellent layers. These properties include the apparent advancing and receding contact angles, the roll-off angle, tensile and lateral adhesion, the impalement pressure, and the observation of drop impact. The most important one is the apparent receding contact angle because it also limits lateral adhesion. The link of these properties to the nano-and microscopic structure of the layer is discussed. Limits, problems, and future challenges are pointed out.

Recent Progress in Preparation of Superhydrophobic Surfaces: A Review

In nature, water-repellency (superhydrophobicity) is found, besides in plants, in insects and bird feathers. The booming field of biomimetics allows one to mimic nature to develop nanomaterials, nanodevices, and processes which offer de- sirable properties. Biomimetics means mimicking biology or nature. Inspired from nature, which reveals excellent su- perhydrophobicity, researchers have recently developed and implemented biomimetic superhydrophobic surfaces in a variety of smart and simple ways. Superhydrophobicity is an effect where surface roughness and chemical composition combine to generate unusual water repellent surface, causing water to bounce and roll off the surface. This review arti- cle provides the overview of the recent progress (within the last four years) in the synthesis, characterization, theoretical modelling, and applications of superhydrophobic surfaces, with focus on the different techniques used and how they have developed over the years. At last, the difficulties related to implementation of superhydrophobic surfaces in day to day life are discussed. This review can find interesting for students, scientists and industrial companies working espe- cially on superhydrophobic surfaces.

Origins of Extreme Liquid Repellency on Structured, Flat, and Lubricated Hydrophobic Surfaces

2018

There are currently three main classes of liquid-repellent surfaces: micro- or nanostructured superhydrophobic surfaces, flat surfaces grafted with "liquidlike" polymer brushes, and lubricated surfaces. Despite recent progress, the mechanistic explanation for the differences in droplet behavior on such surfaces is still under debate. Here, we measure the dissipative force acting on a droplet moving on representatives of these surfaces at different velocities U=0.01-1 mm/s using a cantilever force sensor with submicronewton accuracy and correlate it to the contact line dynamics observed using optical interferometry at high spatial (micron) and temporal (<0.1 s) resolutions. We find that the dissipative force-due to very different physical mechanisms at the contact line-is independent of velocity on superhydrophobic surfaces but depends nonlinearly on velocity for flat and lubricated surfaces. The techniques and insights presented here will inform future work on liquid-...

Super-hydrophobic and super-wetting surfaces: Analytical potential?

The Analyst, 2004

Roughening or texturing surfaces provides super-liquid repellent or film forming properties without alteration of the surface chemistry. These surfaces are easy to produce, can amplify wetting properties and can be either "sticky" or "slippy" to liquids. Their use as waterrepellent coatings is established, but their potential for use in microfluidics and sensor applications remains largely unfulfilled. This article explains several key ideas and suggests why there may be potential for analytical applications.

Superomniphobic Surfaces for Effective Chemical Shielding

Journal of the American Chemical Society, 2013

Superomniphobic surfaces display contact angles >150°and low contact angle hysteresis with essentially all contacting liquids. In this work, we report surfaces that display superomniphobicity with a range of different non-Newtonian liquids, in addition to superomniphobicity with a wide range of Newtonian liquids. Our surfaces possess hierarchical scales of re-entrant texture that significantly reduce the solid−liquid contact area. Virtually all liquids including concentrated organic and inorganic acids, bases, and solvents, as well as viscoelastic polymer solutions, can easily roll off and bounce on our surfaces. Consequently, they serve as effective chemical shields against virtually all liquids organic or inorganic, polar or nonpolar, Newtonian or non-Newtonian. Communication pubs.acs.org/JACS

Biomimetic Coating-free Superomniphobicity

Scientific Reports

Superomniphobic surfaces, which repel droplets of polar and apolar liquids, are used for reducing frictional drag, packaging electronics and foods, and separation processes, among other applications. These surfaces exploit perfluorocarbons that are expensive, vulnurable to physical damage, and have a long persistence in the environment. Thus, new approaches for achieving superomniphobicity from common materials are desirable. In this context, microtextures comprising "mushroom-shaped" doubly reentrant pillars (DRPs) have been shown to repel drops of polar and apolar liquids in air irrespective of the surface make-up. However, it was recently demonstrated that DRPs get instantaneously infiltrated by the same liquids on submersion because while they can robustly prevent liquid imbibition from the top, they are vulnerable to lateral imbibition. Here, we remedy this weakness through bio-inspiration derived from cuticles of Dicyrtomina ornata, soil-dwelling bugs, that contain cuboidal secondary granules with mushroom-shaped caps on each face. Towards a proof-of-concept demonstration, we created a perimeter of biomimicking pillars around arrays of DRPs using a two-photon polymerization technique; another variation of this design with a short wall passing below the side caps was investigated. The resulting gas-entrapping microtextured surfaces (GEMS) robustly entrap air on submersion in wetting liquids, while also exhibiting superomniphobicity in air. To our knowledge, this is the first-ever microtexture that confers upon intrinsically wetting materials the ability to simultaneously exhibit superomniphobicity in air and robust entrapment of air on submersion. These findings should advance the rational design of coating-free surfaces that exhibit ultra-repellence (or superomniphobicity) towards liquids. Liquid-repellent surfaces are utilized in a broad spectrum of applications, such as preventing 1 and harvesting fog 2 , removing bubbles from aqueous feeds 3 , fluid drag reduction and self-cleaning 4 , preventing adhesion of barnacles onto ship hulls 5 , and anti-corrosion coatings 6 , among others 7. In this context, superomniphobic surfaces are known to repel polar and apolar liquids, such as water and hexadecane, respectively, and characterized by advancing and receding contact angles satisfying the empirical relations θ >°150

A novel and inexpensive technique for creating superhydrophobic surfaces using Teflon and sandpaper

Journal of Physics D: Applied Physics, 2010

Great efforts have been spent over the last decade developing hydrophobic surfaces exhibiting very large contact angles with water. Many of these methods require complex and expensive fabrication techniques. We demonstrate that sanding Teflon can produce superhydrophobic surfaces with advancing contact angles of up to 151° and contact angle hysteresis of less than 4°. Furthermore, we show that a wide range of both advancing contact angles and contact angle hysteresis can be achieved by varying the grit size of the sandpaper, allowing for future hysteresis and contact angle studies. Scanning Electron Microscopy (SEM) images of the roughened surfaces depict the range and amplitude of lengthscales imparted on the surface by the sandpaper, which leads to deeper understanding of the state of wetting on the surface.

Hierarchical roughness of sticky and non-sticky superhydrophobic surfaces

2011

Submitted for the DFD11 Meeting of The American Physical Society Hierarchical roughness of sticky and non-sticky superhydrophobic surfaces MUHAMMAD AKRAM RAZA, STEFAN KOOIJ, AREND VAN SILFHOUT, HAROLD ZANDVLIET, BENE POELSEMA, University of Twente-The importance of superhydrophobic substrates (contact angle >150˚with sliding angle <10˚) in modern technology is undeniable. We present a simple colloidal route to manufacture superstructured arrays with single-and multi-length-scaled roughness to obtain sticky and non-sticky superhydrophobic surfaces. The largest length scale is provided by (multi-)layers of silica spheres (1µm, 500nm and 150nm diameter). Decoration with gold nanoparticles (14nm, 26nm and 47nm) gives rise to a second length scale. To lower the surface energy, gold nanoparticles are functionalized with dodecanethiol and the silica spheres by perfluorooctyltriethoxysilane. The morphology was examined by helium ion microscopy (HIM), while wettability measurements were performed by using the sessile drop method. We conclude that wettability can be controlled by changing the surface chemistry and/or length scales of the structures. To achieve truly non-sticky superhydrophobic surfaces, hierarchical roughness plays a vital role.