Andrei FILIPPOV1, Sergei GLAVATSKIH2, Roman DE LA PRESILLA2, Johan LECKNER3, Öleg ANTZUTKIN1
1Lulea University of Technology, Luleå, Sweden
2KTH Royal Institute of Technology, Stockholm, Sweden
3Axel Christiernsson International AB, Nol, Sweden
One of the ways to prepare conductive greases is to use a conductive additive. Such a conductive additive may be particles of a conductive solid, carbon nanotubes, or an ionic liquid. An ionic liquid (IL) has advantages, because it may dissociate with ions, providing the required conductivity on the molecular level. At the same time, ILs are exhibiting lubricant-friendly properties and are different from most conventional room-temperature liquids, because of IL’s non-volatility and non-flammability properties. The knowledge of the structure and dynamics of molecules (and ions) is important to understand the properties of the conductive greases, which are related to their mechanical strengths and electrical/ionic conductivity.
Multinuclear 1H, 11B, and 31P NMR study in a PAO-10 oil, a polypropylene grease, and in 10 wt.% mixtures of the grease with three selected non-halogenated phosphonium ILs composed of the [P6,6,6,14]+ cation and [BOB]-, [BMB]- and [BEHP]- anions demonstrates molecular and ionic mobilities in the range of temperatures 295-363 K. 1H diffusion decays revealed a presence of two fractions of NMR signals from protons: one of those has properties typical for ‘free’, i.e. non-restricted diffusion, while the other fraction corresponds to restricted translational mobility in the formed network of thickener fibers. Analyses of temperature dependences of diffusivities revealed the presence of two phases in the PAO-10 oil and in the grease in the temperature range 299-313 K. Based on 1H diffusivity data, peculiarities of a phase transformation in the PAO-10 oil were investigated and putative mechanisms were suggested. The ‘two-phase’ phenomenon has disappeared in the presence of admixed ionic liquids. Diffusivities of ions from ILs admixed to the grease, measured by multinuclear 1H, 11B, and 31P NMR, are higher than those in neat ILs. Activation energies of diffusion of ions are lower in greases with admixed ILs in comparison with neat ILs.
The Swedish Foundation for Strategic Research (project EM16-0013) is gratefully acknowledged for the financial support.