UV-induced modulation of tribological characteristics: Elastomeric materials featuring controlled anisotropic friction properties

The design of tribologically optimized structures has gained importance in various fields of elastomeric applications ranging from the health care sector to the automotive industry. While many attempts towards improved surface characteristics have been made in recent years, this contribution highlights a new innovative two-step surface modification strategy for enhanced friction properties. Using versatile thiol-ene chemistry, tailored surface structures are architected by means of spatially controlled immobilization of micro-scaled inorganic particles onto natural rubber materials. The chemical composition of the surface was monitored prior to and after its functionalization by XPS, FTIR, zeta potential and contact angle measurements. Physical transformation was analyzed through optical, scanning electron and confocal microscopy in order to gauge surface topology and roughness whilst tribological studies were performed to characterize the friction properties in two dimensions. Upon flood UV exposure, randomly attached particles lead to a considerable increase in surface roughness, which correlates with a nearly linear decrease of the coefficient of friction. A distinctive change of overall surface roughness and decrease of surface friction, respectively, was conveniently adjusted through a variation of particle concentration during the sample preparation step. Whilst elastomer surfaces with randomly attached particles exhibit isotropic coefficients of friction, anisotropic friction properties can be accomplished by controlled surface patterning. The photochemical modification route allows the design of tailored surface textures by photolithographic processes generating appropriate particle-covered geometries on the surface. This strategy leads to the precise preparation of surface textures and thus enables the design of elastomeric materials with tailored two-dimensional friction properties.