Friction in a tribological system can be modified in many ways, e.g. by topography, additive chemistry, lubricant viscosity or subsurface microstructural properties. Typically, the friction of a tribosystem cannot be actively altered. However, the possibility of controllable friction may in principle be of interest for various applications.

In the talk, different approaches will be presented on how friction can be reversibly controlled via functionalization of lubricants and polymers with light-responsive groups. As one approach, different lubricants (PDMS, PAG, triglycerides) are functionalized and characterized in the rheometer and in the ball-on-three-plates geometry. Anthracene groups in functionalized lubricant molecules enable crosslinking and thus viscosity increase due to chain elongation under UV irradiation (365 nm wavelength), Figure 1. The viscosity change can be reversed via heat input or UV irradiation of lower wavelength.

In a second approach, the change of friction of solid surfaces can be excited by modifying polymers (PDMS, COC) with anthracene groups and spiropyran compounds. Results of characterizations in the microtribometer are shown and possibilities and limitations of the different approaches are discussed. The viscosity changes over more than one order of magnitude and changes in the coefficient of friction of more than 100 % can be very interesting for various technical applications.