Function-led design of multifunctional stimuli-responsive superhydrophobic surface based on hierarchical graphene-titania nanocoating

Multifunctional smart superhydrophobic surface with full-spectrum tunable wettability control is fabricated through the self-assembly of the graphene and titania nanofilm double-layer coating. Advanced microfluidic manipulative functions, including directional water transport, adhesion & spreading controls, droplet storage & transfer, and droplet sensing array, can be readily realized on this smart surface. An in-depth mechanism study regarding the underlying secrets of the tunable wettability and the UV-induced superhydrophilic conversion of anatase titania are also presented

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

Printing surface charge as a new paradigm to program droplet transport

Directed, long-range and self-propelled transport of droplets on solid surfaces, especially on water repellent surfaces, is crucial for many applications from water harvesting to bio-analytical devices. One appealing strategy to achieve the preferential transport is to passively control the surface wetting gradients, topological or chemical, to break the asymmetric contact line and overcome the resistance force. Despite extensive progress, the directional droplet transport is limited to small transport velocity and short transport distance due to the fundamental trade-off: rapid transport of droplet demands a large wetting gradient, whereas long-range transport necessitates a relatively small wetting gradient. Here, we report a radically new strategy that resolves the bottleneck through the creation of an unexplored gradient in surface charge density (SCD). By leveraging on a facile droplet printing on superamphiphobic surfaces as well as the fundamental understanding of the mechanisms underpinning the creation of the preferential SCD, we demonstrate the self-propulsion of droplets with a record-high velocity over an ultra-long distance without the need for additional energy input. Such a Leidenfrost-like droplet transport, manifested at ambient condition, is also genetic, which can occur on a variety of substrates such as flexible and vertically placed surfaces. Moreover, distinct from conventional physical and chemical gradients, the new dimension of gradient in SCD can be programmed in a rewritable fashion. We envision that our work enriches and extends our capability in the manipulation of droplet transport and would find numerous potential applications otherwise impossible.Comment: 11 pages, 4 figure

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

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

Tailoring solid-liquid interactions to control droplet wetting and dynamics

2019 Summer.Includes bibliographical references.Recent advances in micro/nano-scale fabrication techniques and synthesis of novel chemicals with a variety of functionalities have opened up new avenues in tailoring solid-liquid interactions. In this work, by systematically tuning the wettability and slipperiness of solid surfaces, we developed a multitude of novel surfaces and strategies. First, we developed metamorphic superomniphobic surfaces that display wetting transition in response to heat. Second, we systematically studied the dynamics of droplets of various liquids during coalescence-induced jumping on textured super-repellent surfaces. Third, we developed a simple and passive strategy consisting of superomniphobic surfaces with a protruding macrotexture to demonstrate coalescence-induced jumping with significantly higher energy conversion efficiency, compared to state-of-the-art surfaces. Fourth, we developed a simple "grafting to" technique to fabricate a novel non-textured hydrophilic surface that is counterintuitively slippery with unprecedented potential to enhance the heat transfer coefficient in dropwise condensation. Fifth, we developed a novel triboelectric-based droplet manipulation technique on smooth hydrophobic slippery surfaces that is very simple without any complex fabrication of manipulation platform or expensive actuation system. Overall, the novel surfaces and strategies developed in this work have significant implications for phase-change heat transfer, liquid transportation, anti-fouling, self-cleaning, drag reduction, corrosion control, and manipulation of liquid droplets