Biofouling is generally undesirable for many applications. An overview of the medical, marine and industrial fields susceptible to fouling is presented. Two types of fouling include biofouling from organism colonization and inorganic fouling from non-living particles. Nature offers many solutions to control fouling through various physical and chemical control mechanisms. Examples include low drag, low adhesion, wettability (water repellency and attraction), microtexture, grooming, sloughing, various miscellaneous behaviours and chemical secretions. A survey of nature's flora and fauna was taken in order to discover new antifouling methods that could be mimicked for engineering applications. Antifouling methods currently employed, ranging from coatings to cleaning techniques, are described. New antifouling methods will presumably incorporate a combination of physical and chemical controls.
Living nature is the inspiration for many innovations and continues to serve as an invaluable resource to solve technical challenges. We find that unique surface characteristics of rice leaves and butterfly wings combine the shark skin (anisotropic flow leading to low drag) and lotus (superhydrophobic and self-cleaning) effects, producing what we call here the rice and butterfly wing effect. A systematic study has been conducted with rice leaves and butterfly wings, using a combination of actual and replica samples. In order to mimic the rice and butterfly wing effect, replica rice leaf and shark skin samples received a superhydrophobic and low adhesion nanostructured coating. The data are compared to those of uncoated samples of fish scales and shark skin. Surface morphology characterization is conducted with SEM and optical profiler imaging using software analysis. Drag is determined with pressure drop measurements from replica lined rectangular duct flow channels (using water and air in laminar and turbulent regimes). The lotus effect is shown with self-cleaning, contact angle, and adhesion force measurements. Results are discussed and conceptual models shown describing the role of surface structures related to low drag, self-cleaning, and antifouling properties.
Researchers are continually inspired by living nature to solve complex challenges. For example, unique surface characteristics of rice leaves and butterfly wings combine the shark skin (anisotropic flow leading to low drag) and lotus leaf (superhydrophobic and self-cleaning) effects, producing the so-called rice and butterfly wing effect. In this paper, we present an overview of rice leaf and butterfly wing fluid drag and self-cleaning studies. In addition, we examine two other promising aquatic surfaces in nature known for such properties, including fish scales and shark skin. Morphology, drag, self-cleaning, contact angle, and contact angle hysteresis data are presented to understand the role of wettability, viscosity, and velocity. Liquid repellent coatings are utilized to recreate or combine various effects. Discussion is provided along with conceptual models describing the role of surface structures related to low drag, self-cleaning, and antifouling properties. Modeling provides design guidance when developing novel low drag and self-cleaning surfaces for applications in the medical, marine, and industrial fields.
Engineering marvels found throughout living nature continually provide inspiration to researchers solving technical challenges. For example, skin from fast-swimming sharks intrigue researchers since its low-drag riblet microstructure is applicable to many low drag and self-cleaning (antifouling) applications. An overview of shark skin related studies that have been conducted in both open channel (external) and closed channel (internal) fl ow experiments is presented. Signifi cant work has been conducted with the open channel fl ow, and less with closed channel fl ow. The results provide design guidance when developing novel low drag and self-cleaning surfaces for applications in the medical, marine, and industrial fi elds. Experimental parameters include riblet geometry, continuous and segmented confi gurations, fl uid velocity (laminar and turbulent fl ow), fl uid viscosity (water, oil, and air), closed channel height dimensions, wettability, and scalability. The results are discussed and conceptual models are shown suggesting the effect of viscosity, coatings, and the interaction between vortices and riblet surfaces. FEATURE ARTICLEeffectively reduce drag in open and closed channel fl ow, although limited data is available with closed channel. Furthermore, closed channel experiments have been conducted to study the neighboring wall effects by using so-called microsized closed channels. In open channel, drag has been measured using water, [47][48][49][50][51] oil, [52][53][54][55] and air. [ 39 , 53 , 56-64 ] Similarly, in closed channel fl ow, drag has been measured using water, [ 47 , 51 , 65,67 ] oil, [ 68 ] and air. [ 67 , 69,70 ] Both drag (for open channel) and the pressure drop (for closed channel) measurements characterize the riblet drag reduction effi ciency.Previous experiments have utilized a variety of riblet geometries, confi gurations, materials, fl uids, and fl ow conditions (laminar and turbulent fl ow). Geometries include blade, sawtooth, scalloped, and bullnose geometries with continuous and segmented (aligned and staggered) confi gurations in water, oil, and air. Open channel oil experiments with metal riblets show drag reduction of nearly 10%, [ 52 ] whist closed channel order to catch prey. [ 40,41 , 43 ] The subsequent increased fl uid fl ow velocity at the skin reduces microorganism settlement time and promotes antifouling. [ 37,38 , 42 ] In addition, microorganisms larger than the spacing between riblets are unable to effectively adhere to and ultimately colonize the skin, which further promotes antifouling. [ 5 , 44-46 ] Low drag and antifouling surfaces have been the subject of much experimentation using shark skin riblet-inspired microtextured surfaces. An ideal surface would withstand harsh environments, adhere to a variety of substrates, combine both low drag and antifouling properties, and be relatively inexpensive.Determining the optimal riblet surface morphology for maximum drag reduction has been the focus of many efforts. Experimental results indicate that shark skin in...
In search of new solutions to complex challenges, researchers are turning to living nature for inspiration. For example, special surface characteristics of rice leaves and butterfly wings combine the shark skin (anisotropic flow leading to low drag) and lotus leaf (superhydrophobic and self-cleaning) effects, producing the so-called rice and butterfly wing effect. In this paper, we study four microstructured surfaces inspired by rice leaves and fabricated with photolithography techniques. We also present a method of creating such surfaces using a hot embossing procedure for scaled-up manufacturing. Fluid drag, self-cleaning, contact angle, and contact angle hysteresis data are presented to understand the role of sample geometrical dimensions. Conceptual modeling provides design guidance when developing novel low drag, self-cleaning, and potentially antifouling surfaces for medical, marine, and industrial applications.
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