Characterization of ultrahydrophobic hierarchical surfaces fabricated using a single-step fabrication methodology (original) (raw)
Related papers
Microstructure Design for Artificial Superhydrophobic Surfaces
International Journal of Engineering and Advanced Technology, 2020
Superhydrophobic surfaces are the surfaces that do not allow the droplets of liquid to spread and wet it. Ideally, the droplets remain almost spherical in shape and with a very small angle of tilt, slide away from the surface. This occurs due to very high contact angle. A perfectly spherical droplet would make 1800 angle of contact, but practically this high contact angle is never possible for a stable droplet. The surfaces that make contact angle (CA)>90o are said to be hydrophobic surfaces. If CA is greater than 150o , the surface is known as superhydrphobic surface. This property of the surface is termed as superhydrophobicity. In this paper, the surface morphology to be engineered is studied, which is governed by certain principles. Theories of Thomas Young [1], Wenzel [2] and Cassie-Baxter [3] are reviewed and effect of micro and nano level of roughness, producing hierarchical structures is analyzed. Subsequently, the designing of such super hydrophobic surfaces is attempted.
Effects of Hierarchical Surface Roughness on Droplet Contact Angle
Langmuir : the ACS journal of surfaces and colloids, 2015
Superhydrophobic surfaces often incorporate roughness on both micron and nanometer length scales, although a satisfactory understanding of the role of this hierarchical roughness in causing superhydrophobicity remains elusive. We present a two-dimensional thermodynamic model to describe wetting on hierarchically grooved surfaces by droplets for which the influence of gravity is negligible. By creating wetting phase diagrams for droplets on surfaces with both single-scale and hierarchical roughness, we find that hierarchical roughness leads to greatly expanded superhydrophobic domains in phase space over those for a single scale of roughness. Our results indicate that an important role of the nanoscale roughness is to increase the effective Young's angle of the microscale features, leading to smaller required aspect ratios (height to width) for the surface structures. We then show how this idea may be used to design a hierarchically rough surface with optimally high contact angles.
Superhydrophobicity Due to the Hierarchical Scale Roughness of PDMS Surfaces
Langmuir, 2008
Wettability control has been widely investigated in the last decades for technological applications such as microfluidic devices and self-cleaning surfaces by modifying both the chemical composition and the geometric structure of the surfaces. Inspired by the typical morphology of superhydrophobic leaves (such as lotus leaves), we have developed a dual-scale roughness, micro-and nanosized, on polydimethylsiloxane (PDMS) surfaces. By combining different geometric parameters and plasma treatment conditions, the structures were controlled hierarchically, at different independent length scales. Both the microsized replicated pillars and the nanosized etched posts tuned the wettability of the PDMS surfaces in a very simple way, up to contact angles of 170°. Furthermore, changes in the influence of micro-and nanoscale geometrical structures were investigated. Hysteresis and contact angles of water droplets are evaluated as a combined effect of micropillars and a superimposed roughness, resulting in high advancing contact angles and low sliding angles.
Wetting and Dewetting Transitions on Hierarchical Superhydrophobic Surfaces
Langmuir, 2011
Many natural superhydrophobic structures have hierarchical two-tier roughness which is empirically known to promote robust superhydrophobicity. We report the wetting and dewetting properties of two-tier roughness as a function of the wettability of the working fluid, where the surface tension of water/ethanol drops is tuned by the mixing ratio, and compare the results to one-tier roughness. When the ethanol concentration of deposited drops is gradually increased on one-tier control samples, the impalement of the microtier-only surface occurs at a lower ethanol concentration compared to the nanotier-only surface. The corresponding two-tier surface exhibits a two-stage wetting transition, first for the impalement of the microscale texture and then for the nanoscale one. The impaled drops are subsequently subjected to vibration-induced dewetting. Drops impaling one-tier surfaces could not be dewetted; neither could drops impaling both tiers of the two-tier roughness. However, on the two-tier surface, drops impaling only the microscale roughness exhibited a full dewetting transition upon vibration. Our work suggests that two-tier roughness is essential for preventing catastrophic, irreversible wetting of superhydrophobic surfaces.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2018
Highlights Microstructured surfaces are developed for various hydrophobicity values An experimental and analytical study has been conducted to investigate the influence of micronano-textured surfaces on the liquid wetting phenomena. The wetting phenomena with different microstructured surfaces as well as an unstructured surface have been evaluated Experimental results of droplet contact angle and surface energy are then compared with analytical calculations (thermodynamic model and capillary Laplace equation) Experimental results reveal that the average water contact angle increases by 34.5 % and 52.5 % for the square-grooved and v-grooved surface, respectively. The surface coating of the square-grooved surface has a larger average contact angle than the Vgrooved surface by 4.6 %.
Nanostructures Increase Water Droplet Adhesion on Hierarchically Rough Superhydrophobic Surfaces
Langmuir, 2012
Hierarchical roughness is known to effectively reduce the liquid−solid contact area and water droplet adhesion on superhydrophobic surfaces, which can be seen for example in the combination of submicrometer and micrometer scale structures on the lotus leaf. The submicrometer scale fine structures, which are often referred to as nanostructures in the literature, have an important role in the phenomenon of superhydrophobicity and low water droplet adhesion. Although the fine structures are generally termed as nanostructures, their actual dimensions are often at the submicrometer scale of hundreds of nanometers. Here we demonstrate that small nanometric structures can have very different effect on surface wetting compared to the large submicrometer scale structures. Hierarchically rough superhydrophobic TiO 2 nanoparticle surfaces generated by the liquid flame spray (LFS) on board and paper substrates revealed that the nanoscale surface structures have the opposite effect on the droplet adhesion compared to the larger submicrometer and micrometer scale structures. Variation in the hierarchical structure of the nanoparticle surfaces contributed to varying droplet adhesion between the high-and low-adhesive superhydrophobic states. Nanoscale structures did not contribute to superhydrophobicity, and there was no evidence of the formation of the liquid−solid−air composite interface around the nanostructures. Therefore, larger submicrometer and micrometer scale structures were needed to decrease the liquid−solid contact area and to cause the superhydrophobicity. Our study suggests that a drastic wetting transition occurs on superhydrophobic surfaces at the nanometre scale; i.e., the transition between the Cassie−Baxter and Wenzel wetting states will occur as the liquid−solid−air composite interface collapses around nanoscale structures. Consequently, water adheres tightly to the surface by penetrating into the nanostructure. The droplet adhesion mechanism presented in this paper gives valuable insight into a phenomenon of simultaneous superhydrophobicity and high water droplet adhesion and contributes to a more detailed comprehension of superhydrophobicity overall.
2010
The engineering of liquid behavior on surfaces is important for infrastructure, transportation, manufacturing, and sensing. Surfaces can be rendered superhydrophobic by microstructuring, and superhydrophobic devices could lead to practical corrosion inhibition, selfcleaning, fluid flow control, and surface drag reduction. To more fully understand how liquid interacts with microstructured surfaces, this dissertation introduces a direct method for determining droplet solid-liquid-vapor interfacial geometry on microstructured surfaces. The technique performs metrology on molten metal droplets deposited onto microstructured surfaces and then frozen. Unlike other techniques, this visualization technique can be used on large areas of curved and opaque microstructured surfaces to determine contact line. This dissertation also presents measurements and models for how curvature and flexing of microstructured polymers affects hydrophobicity. Increasing curvature of microstructured surfaces leads to decreased slide angle for liquid droplets suspended on the surface asperities. For a surface with regularly spaced asperities, as curvature becomes more positive, droplets suspended on the tops of asperities are suspended on fewer asperities. Curvature affects superhydrophobicity because microscopic curvature changes solid-liquid interaction, pitch is altered, and curvature changes the shape of the three phase contact line. This dissertation presents a model of droplet interactions with curved microstructured surfaces that can be used to design microstructure geometries that maintain the suspension of a droplet when curved surfaces are covered with microstructured polymers. Controlling droplet dynamics could improve microfluidic devices and the shedding of liquids from expensive equipment, preventing corrosion and detrimental performance. This dissertation demonstrates redirection of dynamic droplet spray with anisotropic microstructures.
Superhydrophobic surfaces review: Functional application, fabrication techniques and limitations
Journal of Micromanufacturing
Over the years, researchers have been working to mimic the nature by inducing superhydrophobic properties into a variety of material surfaces so that they exhibit non-wetting properties. Many diverse applications have been found in the fields, such as space and aerospace, defence, automotive, biomedical applications and engineering, sensors, apparels, and so on. Superhydrophobic surfaces repel water generally due to their surface texture or chemical properties. In this article, we focus on the functional applications of the superhydrophobic surfaces, and state-of-the-art fabrication technologies and processes, and the limitations of these processes to generate the superhydrophobic surfaces have been developed over the years.
2016
In the past decade, there have been numerous examples of surfaces created with novel functionalities. These functional surfaces are predicted to have a massive impact on a range of commercial sectors within the next five years. Most realized functional surfaces rely on tailored microand nanoscale roughness, which cannot be produced with current mass fabrication technologies. The technology platform needed to create these surfaces has to be directly compatible with current mass production platforms, to commercially realize microand nanotextured surfaces. This comparability can be achieved by direct microand nanostructuring of commerical injection molding tools to create the desired surface structures directly in the molding process. The aim of this project was to enable the fabrication of surfaces with controlled wetting by injection molding. During the project, I have demonstrated improvements in many of the fields related to mass-fabrication of water repellent surfaces. Including: ...