Patterning Of Surfaces To Control The Storage, Mobility And Transport Of Liquids For Microfluidic Applications

Systems and methods to pattern surfaces to create regions of variable adhesive force on a superhydrophobic paper surface. By taking advantage of high surface energy sticky islands on a non-sticky superhydrophobic surface, microliter water drops can be registered or confined at specific locations; selected drops can then be transferred to another patterned substrate and the drops mixed and/or allowed to react without the need for pipettes or other fluid transfer tool.Georgia Tech Research Corporatio

Exploitation of Super(de)wettability via Scalable Hierarchical Surface Texturing

The field of wettability is an age-old topic that has been revitalized in the last two decades. Historically, the diverse physical phenomena of wetting has influenced the development of inventions that dates back to the paleolithic era (2,600,000 to 10,000 BC) in the form of charcoal and ochre -based cave paintings, or the mesolithic (10,000 to 5,000 BC) and neolithic (5,000 to 2,000 BC) periods as pottery and soaps. Since the end of the Stone Age, human civilizations and scientific discoveries have progressed by leaps and bounds. Despite the advances in metallurgy, optics, chemistry, mechanics, mathematics and electricity, our understanding of fluid-surface interactions remained stagnant until 1804. Between 1804 and 1805, Thomas Young described the concept of a wetting contact angle, which controls the equilibrium shape of a fluid droplet on a surface, thus making wettability a quantified branch of physics. The late entry of this scientific field is astounding, considering the ubiquitousness of water on Earth. Despite Young’s discoveries, the area remained largely unexplored. Work on wettability was intermittent, with Edward Washburn on capillary effects in 1921 and later on, Robert Wenzel and Cassie-Baxter in 1936 and 1944 on the wetting of rough interfaces. In 1997, almost exactly 20 years ago, the field was rejuvenated by the corresponding discoveries of superhydrophilicity (water droplets spread into a sheet) and superhydrophobicity (water droplets ball up), by Wang et al. and Neinhuis et al. respectively. Since their work into these distinct super(de)wetting states, the field has grown exponentially. Today, its revival can be attributed to biomimetics (engineering mimicry / imitation of life) and a revolutionized understanding behind super(de)wetting mechanisms that are found in nature. The precise combination of hierarchical (multi-scale) texturing with select surface chemical composition is vital towards fabricating interfaces with specialized wetting properties. Knowledge behind the careful control of surface texturing holds immense potential for enabling a plethora of user-defined functional interfaces. As of the time of writing, the field of wettability encompasses multiple domains, such as superhydrophilicity (water-loving),[8] slippery superhydrophobicity (water-fearing), adhesive superhydrophobicity (an unintuitive love-fear relationship with water), superoleophobicity (oil-fearing), superamphiphobicity (water- and oil-fearing),[11] superomniphobicity (all-fearing) as well as a range of other important intermediary, cross-environment wetting states. Methods employed for achieving super(de)wettability can be broadly classified under 2 sub-classes. The first relies on intricate top-down photolithography (-drawing with light) or templating-based designs while the other uses the realms of chaotic, but deterministic and scalable bottom-up self-assembly. Both routes are promising for the development of unique super(de)wetting states, albeit with considerable drawbacks on both fronts. For instance, while lithography and templating have demonstrated exemplary surface texturing precision and super(de)wetting performance, these methods remain limited by poor scalability, complexity and costs in instrumentation and operation. Alternatively, scalable and cheap bottom-up self-assembly methods can exist within complex electro-, hydro-, aero-, thermal- or thermo-dynamically varied regimes. Consequently, each system requires intense cross-optimization research efforts in determining niche operating parameters. In this work, we explore a series of highly promising hierarchically structured material interfaces that were enabled by understanding, taming and controlling scalable but chaotic bottom-up methods. To this end, we demonstrate their potential within the entire super(de)wetting spectrum, showcased through a series of coatings and further exemplified by functional micro(fluid)mechanical systems (M-F-MS)

TiO2 -Based Surfaces with Special Wettability – From Nature to Biomimetic Application

Super-wetting/antiwetting surfaces with extremely high contrast of surface energy and liquid adhesion have attracted a lot of interest in both fundamental research and industry. Various types of special wetting surfaces can be constructed by adjusting the topographical structure and chemical composition. In this chapter, recent advance of the super-wetting/antiwetting surfaces with special solid/liquid adhesion has been reviewed, with a focus on the biomimetic fabrication and applications of TiO2-based surfaces. Special super-wettability examples include lotus-leaf-inspired surfaces with low adhesion, rose-petal-inspired surfaces with high adhesion, spider silk bio-inspired surfaces with directional adhesion, fish-scale-inspired underwater superoleophobic surface, and artificial surfaces with controllable or stimuli-responsive liquid adhesion. In addition, we will review some potential applications related to artificial antiwetting surface with controllable adhesion, e.g., self-cleaning, antifogging/anti-icing, micro-droplet manipulation, fog/water collection, water/oil separation, anti-bioadhesion, micro-template for patterning, and friction reduction. Finally, the difficulty and prospects of this renascent and rapidly developing field are also briefly proposed and discussed

Anti-icing property of bio-inspired micro-structure superhydrophobic surfaces and heat transfer model

Ice accumulation is a thorny problem which may inflict serious damage even disasters in many areas, such as aircraft, power line maintenance, offshore oil platform and locators of ships. Recent researches have shed light on some promising bio-inspired anti-icing strategies to solve this problem. Inspired by typical plant surfaces with super-hydrophobic character such as lotus leaves and rose petals, structured superhydrophobic surface are prepared to discuss the anti-icing property. 7075 Al alloy, an extensively used materials in aircrafts and marine vessels, is employed as the substrates. As-prepared surfaces are acquired by laser processing after being modified by stearic acid for 1 h at room temperature. The surface morphology, chemical composition and wettability are characterized by means of SEM, XPS, Fourier transform infrared (FTIR) spectroscopy and contact angle measurements. The morphologies of structured as-prepared samples include round hump, square protuberance and mountain-range-like structure, and that the as-prepared structured surfaces shows an excellent superhydrophobic property with a WCA as high as 166 ± 2°. Furthermore, the anti-icing property of as-prepared surfaces was tested by a self-established apparatus, and the crystallization process of a cooling water on the sample was recorded. More importantly, we introduced a model to analyze heat transfer process between the droplet and the structured surfaces. This study offers an insight into understanding the heat transfer process of the superhydrophobic surface, so as to further research about its unique property against ice accumulation

Tuning the interaction of droplets with liquid-repellent surfaces: fundamentals and applications

2018 Fall.Includes bibliographical references.Liquid-repellent surfaces can be broadly classified as non-textured surfaces (e.g., smooth slippery surfaces on which droplets can slide easily) and textured surfaces (e.g., super-repellent surfaces on which liquid droplets can bead up and roll off easily). The liquid repellency of smooth slippery surfaces can be adjusted by tuning the surface chemistry. The liquid repellency of super-repellent surfaces can be adjusted by tuning the surface chemistry and surface texture. In this work, by systematically tuning the surface chemistry and surface texture and consequently the surface wettability of solid surfaces, the interaction of droplets of various liquids on liquid-repellent surfaces has been investigated. Based on this understanding, the following phenomena/applications have been investigated/developed: (i New methodology to sort liquid droplets based on their surface tension: By tuning the surface chemistry and surface texture of solid surfaces, we tuned the mobility of liquids with different surface tension on super-repellent surfaces. Utilizing this, we fabricated a simple device with precisely tailored domains of surface chemistry that can sort droplets by surface tension. (ii) New approach to detect the quality of fuel blends: By tuning the surface chemistry of solid surfaces, we investigated the interaction of fuel blends with liquid-repellent surfaces. Based on the understanding gained, we fabricated a simple, field-deployable, low-cost device to rapidly detect the quality of fuel blends by sensing their surface tension with significantly improved resolution. (iii) Novel materials with improved hemocompatibility: By systematically tuning the surface chemistry and surface texture and consequently the surface wettability of solid surfaces, we investigated the interaction of blood with super-repellent surfaces. Based on the understanding gained, we fabricated super-repellent surfaces with enhanced hemocompatibility. (iv) Advanced understanding of droplet splitting upon impacting a macroscopic ridge: By systematically tuning the ridge geometry, we investigated the interaction of impacting water droplets with super-repellent ridges. Based on the understanding gained, we demonstrated the scaling law for predicting the height from which water droplets should fall under gravity onto a super-repellent ridge for them to split into two smaller droplets

Ultralow Icing Adhesion of a Superhydrophobic Coating Based on the Synergistic Effect of Soft and Stiff Particles.

A novel superhydrophobic coating composed of soft polydimethylsiloxane microspheres and stiff SiO2 nanoparticles was developed and prepared. This superhydrophobic coating showed excellent superhydrophobicity with a large water contact angle of 171.3° and also exhibited good anti-icing performance and ultralow icing adhesion of 1.53 kPa. Furthermore, the superhydrophobic coating displayed good icing/deicing cycle stability, in which the icing adhesion was still less than 10.0 kPa after 25 cycles. This excellent comprehensive performance is attributed to stress-localization between ice and the surface, resulting from the synergistic effect of soft and stiff particles. This work thus opens a new avenue to simultaneously optimize the anti-icing and icephobic performance of a superhydrophobic surface for various applications

Novel Fabrication of Un-coated Super-hydrophobic Aluminum via Pulsed Electrochemical Surface Modification

AbstractSuper-hydrophobic and super-hydrophilic aluminum (Al) surfaces were fabricated via electrochemical surface modification (ECSM) in neutral NaClO3 electrolyte without the addition of secondary chemical coatings. The effects of processing time and applied potential on the surface roughness and wettability were studied. The aluminum surface was characterized using stylus profilometer and scanning electron microscope (SEM). Wettability was evaluated using Sessile Drop Test and a high resolution camera. Results show that surfaces obtained hierarchical rough features and super-hydrophilic behavior after pulse electrochemical machining. Heat treatment at 200°C transitioned the substrates to exhibit super-hydrophobic behavior due to the removal of all moisture from within the micro- and nano-meter scale features on the aluminum surfaces, allowing for the reformation of a natural passivation (oxide) layer with atmospheric interaction. The method proposed in this study for producing super-hydrophobic aluminum surfaces does not require the use of acid or base etching or chemical coatings, such as flouroalkylsilane (FAS). Experimental results reveal increase in contact angle, with increase in applied potential, and decrease in sliding angle