Wet sliding friction of elastomer compounds on a rough surface under varied lubrication conditions

'Green' tire bearing tread rubber reinforced with precipitated silica can exhibit improved wet traction performance. The underlying mechanism is currently not well understood. To improve our capability of rational material design for enhanced driving safety, wet sliding friction for various rubber compounds is tested on a Portland cement concrete surface under varied lubrication conditions. The wetting liquid is either ethanol or water, and the initial amount of liquid on the concrete surface is adjusted. Sliding friction is detected to alter with lubrication condition. Under ethanol lubrication, the sliding friction is markedly lower than that under water lubrication. Additionally the benefit in wet traction from silica is significantly diminished or eliminated in ethanol. Such observations cannot be rationalized with simple considerations of rubber bulk viscoelasticity, liquid viscosity, cavitation, or capillary effect. We believe that these observations strongly indicate the significance of interfacial interactions in determining the wet sliding friction of elastomer compounds. The potential relevance of capillary porosity in concrete and Marangoni drying effect to wet traction is also introduced.