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 (LGF) and their nitrogen-doped analogs (N-LGF) in three commercially available plastic lubricants (PLM I–III) and in a model base lubricant—medical vaseline (VM) were studied by the method of oscillatory deformations. The concentration range of additives of carbon nanostructures varied from 0.1 to 1.5 wt %. At concentrations from 0.1 to 0.5 wt %, dispersions retain the viscoelastic properties of the basic PLM. At concentrations of 1.0 and 1.5 wt %, the dispersion passes into the region of a viscous state. The predominant contribution to the change in the viscoelastic properties of dispersions is the type of base substrate. Nevertheless, the effect of structural features of LGF and N-LGF additives can be clearly seen by the example of their dispersions in VM, which does not contain thickeners and other additives. The use of the Maxwell model for a viscoelastic body allowed calculating the relaxation time and correlation length of the thickener skeleton as well as explaining the change in these parameters for the studied dispersions with varying concentrations of nanocarbon structures.