상어표피 모사 리블렛 표면의 젖음성 및 마찰 특성에 관한 연구

Abstract

ABSTRACT

Recently, Biomimetic inspired by nature is studied by many researchers to achieve the improvement of mechanical technology. One field of Biomimetic is about shark skin effect including drug reduction, anti-fouling and self-cleaning beacause the shark skin has the hydrophobicity and oleophobicity by the special surface pattern called on the surface. Usually, researchers focus on the effect of drug reduction on the shark skin or riblet surface. However, anti-fouling and self-cleaning are also important characteristics of the shark skin. Anti-fouling effect prevents to adhere the pollution like the seaweed growing on the shark skin. Also, there is self-cleaning characteristic on the shark skin surface to keep the cleanliness of the surface by water droplet rolling on the surface. By these effects, the shark skin surface can keep the cleanliness of the surface. In this study, shark skin replicas and micro riblet were fabricated by 2 micro-replication methods and WEDG, respectively. To make shark skin replicas, micro-molding - micro-molding method and hot embossing - micro-mol ding method were used. Also, WEDG test rig that can process the steal with half ellipse shape was made to fabricate the replication mold for micro riblet. Contact angles of water and oil droplets were measured on all surfaces to evaluate the hydrophobicity and oleophobicity. Also, dynamic contact angle test related to self-cleaning characteristic was measured by tilting method. The experiments about contact angle of oil droplet was run in two conditions (solid-air-oil interface and solid-water-oil interface). Moreover, all surfaces were coated by Teflon to check the effect of hydrophobic coating. Also, this study made a tribo test having a wide range of normal load from 0.1N~100N to carry out the friction test of micro riblet and flat surface. By the friction test, friction coefficient of micro riblet was measured and compared with flat surface. As a result, shark skin replica I by micro-moling - micro-molding method showed better wettability and better replication than shark skin replica II by hot embossing - micro-molding method. To make replication mold for micro riblet, work condition was 75V, 0 and 30(voltage, capacitance and sensitivity , respectively). All surfaces(shark skin replica I, shark skin replica II and micro riblet) showed hydrophobicity and similar tendency for oleophobicity. However, water droplet was not rolling on the surface because these surfaces have hydrophobic characteristic on the surface but there is petal effect. Also, in the solid-water-oil interface, coated surfaces showed oleophiliciy with much lower contact angle of oil than normal surface because there is water trap on the normal surface but surface tension of water is much weaker than normal surface when the surface was coated. From these results, it was confirmed that wettability of micro riblet showed similar results with wettability of shark skin replica I like shark skin. For the friction test, normal force was 5N and then friction coefficient was measured after the experiment. It was confirmed that friction coefficient of micro riblet was lower than flat surface.