Influence of two types of few-layer graphite fragments on viscoelastic properties of plastic lubricants

The viscoelastic properties of dispersions of few-layer graphite fragments (FLGF) and their nitrogen-doped analogs (N-FLGF) in three commercially available plastic lubricant materials (PLM I-III) and in a model base lubricant, medical vaseline (VM), have been studied by the method of oscillatory deformations. The concentration range of carbon nanostructures additives was varied from 0.1 to 1.5 wt. %. At concentrations from 0.1 to 0.5 wt. % dispersions retain the viscoelastic properties of base PLM. At concentrations of 1.0 and 1.5 wt. % dispersions go into the region of viscous state. The predominant contribution to the change in the viscoelastic properties of dispersions is a type of the base lubricant. Nevertheless, the effect of structural features of LFGF and N-FLGF additives can be clearly seen on the example of the dispersions in VM, which does not contain any thickeners or other additives. The use of the Maxwell model for a viscoelastic body made possible to calculate the relaxation time and correlation length of the thickener skeleton, as well as to explain the change in these parameters for the studied dispersions with varying concentrations of nanocarbon structures.