By comparing Figures 1 and 4, it is immediately seen that all three SWCNT’s were much more efficient thickeners in the PAO blend compared to any of the graphites. This may be due to the intrinsic “fiberlike” structure provided by CNT’s, but absent in the other graphitic solids. The ranking of all carbonbased solids as thickeners in the PAO blend is summarized as follows: SWCNT-3 > SWCNT-1 > SWCNT-2 >> Graphite A > Graphite E > Graphite B > Graphite D > Graphite C Thickening Efficiency and Dropping Points of Combinations of SWCNT’s An experiment was performed to investigate whether there might be an interaction between SWCNT-1 and SWCNT-2 to increase (or decrease) their thickening efficiency when used as co-thickeners in the PAO blend. Two greases (Blends 25 and 26) were made using both SWCNT-1 and SWCNT-2 as cothickeners. Greases 25 and 26 were made as follows. Figure 1 shows the linear regression relationship between carbon thickener content and grease worked penetration for each SWCNT. Using Figure 1, the amounts of each of these SWCNT’s (each as an individual thickener) needed to make hypothetical greases with target worked penetrations of 280 and 310 were determined. Using those predicted values, two grease compositions were prepared that were compositionally equivalent to 50/50 (wt/wt) blends of greases made from only SWCNT-1 and from only SWCNT-2. Greases 25 and 26 would have worked penetration values of 280 and 310 if there were no interactions between the two SWCNT’s. The compositions and test results for Greases 25 and 26 are provided in Table 9. Comparison of actual worked penetrations and theoretical values are given in Figure 5.
- 16 VOLUME 83, NUMBER 4