Wear-Induced Microtopography Evolution and Wetting Properties of Self-Cleaning, Lubricating and Healing Surfaces

Adhesion, friction, and stiction constitute a significant problem for small-sized applications, such as microelectromechanical systems (MEMS) and magnetic storage devices. It has been suggested to use surface texturing to decrease the adhesion force between components in these devices using the so-called Lotus effect (surface roughness induced superhydrophobicity and self-cleaning). However, for applications with high friction, such as head-tape interfaces, wear can deteriorate the microstructure, so the Lotus effect will not last for a long time. To overcome this, we suggest using equilibrium surface roughness, which provides Lotus effect properties. We suggest a thermodynamic model for microtopography evolution and equilibrium roughness due to wear and combine this model with the Wenzel and Cassie theories of wetting. The equilibrium roughness is governed by the minimization of deterioration using the minimum entropy production principle. On the other hand, self-healing/cleaning/lubrication is governed by minimum energy and entropy principles, so the combination of the two approaches is discussed. Examples of evolution of wetting properties due to wear of several cases of rough profiles are discussed and certain recommendations on how to decrease friction are formulated.