The DSCOF shows a rising trend with increasing scratch normal loads, but exceptions exists. In addition, the DSCOF exhibits a decreasing trend with increasing scratch speed. As shown in Fig.3c, the DSCOF exhibits a decreasing trend when the slip agent concentration increases for the range of scratch normal loads from 0 to 5 N. However, at more than 15 N, the order changes because the DSCOF value of MMA-s00 and MMA-s10 decreases in the range of 5-15 N. As khown in Fig.3d, the decreasing slopes of the DSCOF differ across material systems, and the order of the DSCOF is also changed with increasing scratch speed. These exceptions will be explained later with the second critical load which can be defined for variable normal load conditions.