Meeting Abstract
Slippery surfaces are common in biology, and have important roles to play as an interface between organismal tissues and the environment. In particular, mucus coatings on fish have been proposed to reduce drag during swimming. But little is known about the properties of fish mucus, and previous work on fish mucus has focused on static testing and not on analyzing the effects on dynamic, swimming performance. We measured viscous properties of trout mucus using a cone-plate viscometer, and used aluminum plates coated with Krytox viscous lubricant to test the effect of lubricants on swimming thrust and efficiency relative to a smooth and unlubricated control. Trout mucus is non-Newtonian and has a complex composition. We prepared the surface of aluminum panels by functionalizing and texturing them in several ways to hold Krytox lubricant which has a similar viscosity to trout mucus. This process greatly reduced the loss of lubricant during testing. Testing of coated panels relative to controls revealed that the slippery coating enhanced the lift to drag ratio by 2 – 10%. Dynamic testing of swimming panels moved in heave and pitch showed that coated panels improved swimming efficiency by 3 – 5 % over a wide range of motion parameters, and increased thrust of 4% was also observed over nearly the entire range of tested motions. Measurements of boundary layer flows on coated versus uncoated flat plates confirmed that the Krytox slippery coating reduced skin friction drag by ~5% under laminar flow conditions. These results show that slippery coatings can improve swimming performance over a wide range of both static and dynamic conditions, and do not simply enhance propulsion over a limited range of motion parameters.
