Thermal and tribodecomposition mass spectra of polymer-polymer friction pairs.

The goal of the presentation is to quantitatively describe the information obtained by thermal and tribodecomposition experiments in the vacuum chamber of mass-spectrometer (~10^-6 Torr) and atmosphere conditions based on synchronous registration of mass-spectra of volatile molecular products of polymer decomposition, friction force, thermopair measurements of triboinduced heating and calculated flux of the energy generated by friction forces. The physical principles of mass-spectrometric detection of the quantity and the rate of desorption of the molecular decomposition products of macromolecules are preliminary considered based on the dependencies of the registered flux of the decomposition molecular products in vacuum of mass-spectrometer on thermopair measured temperature for the polymer layers of submicron thickness. The examples include the friction between depolymerizing polymers: polymethylmethacrylate, polyoxymethylene, polytetrafluoroethylene and other polymers, e.g. polyamide, as well as friction of the polymers against steel. The polymers used in the study are characterized additionally by differential scanning calorimetry. The experimental correlations between the composition and kinetics of formation of the molecular products, friction force transitions, the character of the triboinduced surface roughness changes and triboinduced vibration energy flux registered with piezoelectric transducer are discussed. Temperature measurements for the experimentally registered friction force kinetic dependencies are compared to finite elements calculations of the thermal problem in the friction geometries used (cylinder-on-flat, ball-on flat, etc.) both in technical approximation of uniform stress distribution as well as in realistic case of non-uniform distributions of friction stress over contact area. The data are compared to the measurements of wear of the polymers expressed as the ratio of the macroscopic loss of mass of the polymer as a result of friction or the mass of the molecules desorbed to the work of friction forces at different levels of energy flux generated by friction forces.